Next Article in Journal
Effect of Ammonium (NH4+) Impurity on the Crystallization of Cobalt Sulfate Hexahydrate from Aqueous Solutions Using Cooling Method
Previous Article in Journal
Advancements in the Electrochemical Upcycling of Waste Plastics into High-Value Products
Previous Article in Special Issue
Noncovalent Interactions in Coordination Chemistry of Cyclic Trinuclear Copper(I) and Silver(I) Pyrazolates
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Crystals
Volume 15
Issue 4
10.3390/cryst15040294
crystals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

On the Importance of Squaramide and Squarate Derivatives as Metal–Organic Framework Building Blocks

by
Catalina Nicolau
,
María de las Nieves Piña
,
Jeroni Morey
* and
Antonio Bauzá
*
Departament de Química, Universitat de les Illes Balears, Ctra. de Valldemossa, km. 7.5, 07122 Palma de Mallorca, Islas Baleares, Spain
*
Authors to whom correspondence should be addressed.
Crystals 2025, 15(4), 294; https://doi.org/10.3390/cryst15040294
Submission received: 28 February 2025 / Revised: 21 March 2025 / Accepted: 21 March 2025 / Published: 24 March 2025
(This article belongs to the Special Issue Reviews of Crystal Engineering)
Browse Figures
Versions Notes

Abstract

:
In this review article the synthesis and solid state structure of squaramide/squarate based metal–organic frameworks (MOFs) are analyzed and discussed. In detail, a thorough search in the literature revealed the successful utilization of these two organic molecules as MOF building blocks capable of catalyzing (i) water splitting reactions, (ii) electrocatalytic oxygen evolution reactions, and (iii) Michael addition reactions. Additionally, some of the highlighted examples also utilized these two molecular synthons to compose MOFs exhibiting gas adsorbent properties, concretely for capturing propadiene and propylene. In each of the selected examples a theoretical study of the noncovalent interactions (NCIs) established between the squaramide/squarate-based MOF and the guest molecules trapped inside was carried out, providing additional information regarding the strength of the MOF–guest interactions, which certainly influence the catalytic/adsorbent capabilities of these materials. We believe that the examples collected herein will be useful for those scientists working in the fields of supramolecular chemistry, crystal engineering, catalysis, and materials science by providing a retrospective guide on the role of squaramide and squarate in the formation of MOFs.

1. Introduction

1.1. MOFs: Concept and General Applications

Metal–organic frameworks (MOFs) represent a unique and highly versatile class of crystalline, porous coordination polymers. The conceptual foundation of MOFs was first formulated by Yaghi in 1995 [1], marking a significant breakthrough in the field of porous materials. These materials have since attracted extensive research interest due to their well-defined structural architectures, rigidity, exceptional porosity, and tunable physicochemical properties. Structurally, MOFs consist of highly ordered molecular assemblies in which organic ligands act as linkers, coordinating with metal ions to form robust, stable frameworks [2,3]. The rational design of MOFs allows for the precise control of their morphology, pore structure, and physicochemical characteristics, making them powerful tools for a wide range of applications, including gas storage [4], catalysis [5,6], drug delivery [7], as well as for optical and electronic applications, depending on the type of metal center involved [8].
One of the most notable features of MOFs is their extraordinarily high specific surface area, which is among the highest recorded for any known material. This property makes them particularly effective for the adsorption and sequestration of small, neutral molecules such as hydrogen (H2), carbon dioxide (CO2), and water (H2O) [4]. The ability to selectively adsorb and store gases has positioned MOFs as promising candidates for gas separation, environmental remediation, and hydrogen storage in energy-related applications [9]. Furthermore, their tunable pore structures allow for selective molecular recognition and separation processes, enhancing their utility in industrial and environmental applications [10].
In addition to their adsorption capabilities, MOFs exhibit remarkable catalytic properties, since the presence of metal ions enables them to act as heterogeneous catalysts, facilitating a variety of chemical transformations [5,6]. The catalytic activity of MOFs can be attributed to the Lewis acidity of the metal centers, which act as active sites along the course of the reaction. By modifying the nature of the metal ions and the surrounding organic ligands, scientists can regulate the catalytic performance of MOFs for specific applications, including organic transformations [11], photocatalysis [12], and electrocatalysis [13]. This tunability extends their applicability to fields such as green chemistry, where MOFs are utilized as potential catalysts for sustainable chemical processes [14]. Beyond catalysis, MOFs have also demonstrated a promising potential in optoelectronic applications [15], owing to their ability to incorporate different metal centers and functional organic linkers for the fine-tuning of electronic, photonic, and luminescent properties, making them suitable for use in light-emitting devices, sensors, and energy conversion systems.

1.2. The Role of the Organic Ligand in MOF Structure and Functionality

Undoubtedly, organic molecular ligands are a fundamental part of the final morphology of MOFs, since they play a crucial role in defining key structural attributes, including pore size, framework rigidity, and the coordination mode with metal centers [16,17,18]. The selection of appropriate organic ligands is therefore a critical step in MOF synthesis, since not all organic molecules possess the required coordination capabilities. In detail, suitable ligands must exhibit a strong coordination ability with metal ions, ensuring the stability and integrity of the resulting framework. Therefore, the range of available organic ligands is limited to those capable of forming robust coordination bonds with metal centers. Typically, the most widely employed organic ligands in MOF synthesis include heterocyclic nitrogen-containing compounds, polycarboxylate systems [19,20], or oxocarbon-based ligands. These ligand classes offer diverse coordination geometries and versatile binding modes, allowing for the formation of structurally diverse MOFs with tailored physicochemical properties. For instance, polycarboxylate ligands, such as terephthalic acid and trimesic acid, are frequently used due to their ability to establish multiple coordination interactions with metal centers, resulting in highly stable frameworks [21]. Similarly, heterocyclic nitrogen-containing ligands, including imidazolate and pyridine derivatives, have been extensively explored for their ability to modulate the electronic and catalytic properties of MOFs [22].
Furthermore, the ability to incorporate multiple ligand types within a single MOF structure offers additional versatility for structural diversification and functional enhancement. By strategically combining ligands with different donor functionalities, particularly those containing both nitrogen- and oxygen-donor moieties, scientists can fine-tune the electronic, catalytic, and adsorption properties of MOFs. This approach significantly expands the synthetic possibilities and enables the design of MOFs with hierarchical pore structures, enhanced chemical stability, and improved selectivity for target applications [23,24]. The introduction of mixed-ligand strategies has also facilitated the development of multifunctional MOFs capable of simultaneously exhibiting gas storage, catalytic, and optical properties, thus broadening their potential applications in advanced materials science [3].

1.3. MOFs: Current Applications

Nowadays, MOFs exhibit a wide range of applications in several areas, such as gas storage [25,26,27,28,29,30], drug delivery [31,32], ion exchange [33], magnetism [34], catalysis [35], chemical sensors [36], non-linear optical properties [37], fluorescence [38], and separation properties [39,40]. Depending on the biocompatibility of the organic ligand and the metal, MOFs have also been used to transport therapeutic agents [41,42]. For this purpose, the metal ions used in the MOF structure must be of a biocompatible nature, leading to the development of MOFs based on Mg2+, Ca2+, Fe3+, Fe2+, and Zn2+, together with other inert metals such as Au, Ag, and Zr [43,44]. In this way the uptake, protection, transport, and release of the drug can be made more effectively and used in anticancer therapy [45]. Alternatively, they can be used for antibacterial control where the antibiotic and MOF metal ions act synergistically to increase the effectiveness of the treatment [46]. Moreover, MOFs have also been used in biochemistry for the immobilization of enzymes [47]. Lastly, taking advantage of the stability of MOFs, promising therapies have been developed based on their use in photodynamic and photothermal therapy [48].
As mentioned above, an interesting feature of MOFs is the combination of different organic ligands with different metal ions, allowing for a better control of the final morphology and resulting pore size. In fact, it is possible to adjust the preparation conditions of MOFs so that they have an even larger pore size than zeolites [49,50,51]. On the other hand, in industrial applications related to the energy sector, the use of MOFs for the separation of hydrocarbons is of great interest and practical difficulty. For this purpose, their combined use along with membranes has attracted much attention from researchers due to their high energy efficiency, low cost, and the possibility of continuous operation [52,53].
In environmental chemistry, an interesting application is related to the recovery of iodine isotopes (129I and 131I) which are environmentally hazardous radionuclides derived from uranium fission due to their high solubility in water. In fact, 129I possesses a half-life of 1.57 × 107 years, thus leading to serious bioaccumulation problems. In this regard, MOFs capable of adsorbing and sequestering both the neutral iodine (I2) and the anionic species (I3−) in an economical and effective manner have been described in the literature [54]. This ability of MOFs to retain neutral molecules has been extended to gaseous systems, leading to the development of specific sensors for gases, particularly volatile organic compounds (VOCs) [55,56].

1.4. MOFs: Challenges and Future Perspectives

Beyond structural and application considerations, recent advances in MOF research have been focused on enhancing their stability, scalability, and practical application. Although many MOFs exhibit excellent crystallinity and porosity under laboratory conditions, their long-term stability under real-world operating conditions remains a critical challenge. Factors such as humidity, temperature fluctuations, and chemical degradation can affect the structural integrity of MOFs, limiting their practical applications. Consequently, scientists have explored post-synthetic modifications and hybridization strategies to enhance MOF stability. Approaches, such as surface functionalization [57], incorporation of secondary building units (SBUs) [58], and the development of composite materials [59], have been employed to improve the chemical and thermal robustness of MOFs. Additionally, the integration of MOFs into polymeric matrices, thin films, and nanocomposites has recently opened new ways for their practical application in membranes, coatings, and heterogeneous catalysis [60].
This review focuses on MOFs containing squaramide/squarate ions as organic ligands in their structure. During our literature survey, we considered the period between 2005 and 2025 and as a result we found a total number of 50 studies, resulting in 36 studies published between 2018 and 2025. From them, we selected several studies devoted to different applications, such as gas capturing and storage or heterogeneous catalysis, which are described more in detail. Furthermore, theoretical calculations on some of them were carried out to understand the physical nature of the noncovalent interactions (NCIs) involving the molecular recognition process between the MOF and the guest molecules present inside their solid state architecture.

1.5. Squaric Acid and Squaramide as MOF Ligands: Main Features and Synthetic Pathways

The squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione, C4O4H2) was first obtained in 1959 by Cohen and collaborators [56] as the hydrolysis product of 1,3,3-triethoxy-2-chloro-4,4-difluorocyclobutene or 1,2-diethoxy-3,3,4,4-tetrafluorocyclobutene (see Figure 1).
Crystals 15 00294 g001
Figure 1. Preparation of squaric acid as reported by Sydney Cohen and coworkers [60].
Figure 1. Preparation of squaric acid as reported by Sydney Cohen and coworkers [60].
Crystals 15 00294 g001
In addition, its corresponding dianion, squarate (C4O42−), is characterized by an unusually high acidity (pKa1 = 0.54; pKa2 = 3.58) (see Figure 2 top). This high acidity, close to that of sulphuric acid (pKa2 = 1.99), is related to the resonance delocalization of the negative charges in the square planar structure between the four oxygen atoms, giving the oxocarbon dianion a highly aromatic character (see Figure 2 bottom) [61,62].
In this context, the formation of methyl, ethyl, propyl, and butyl esters from squaric acid and the corresponding alcohol corresponds to a simple esterification reaction, and these esters, especially dimethyl and diethyl squarate, are commonly used as precursors for the preparation of squaramides (see Figure 3 top). This is carried out by reaction under mild conditions at room temperature, with stirring and in an argon atmosphere for several hours in the presence of an aliphatic primary amine (see Figure 3 bottom).
A further synthetic advantage is the possibility of producing asymmetric squaramides, since the formation of the mono- or disubstituted squaramide can be controlled by the choice of the appropriate solvent [63,64]. Additionally, aromatic primary amines can be obtained; however, it is recommended to use zinc triflate as a catalyst to achieve a good reaction performance [65]. Altogether, these standardized synthetic routes used for the preparation of squaramides normally result in reasonable yields.
On the other hand, squaramides exhibit a very strong dipole moment coming from the –NH– groups of the ring to the carbonyl groups. This global dipole allows squaramides to participate in hydrogen bond formation as both donor and acceptor counterparts. In the case of squaramides, the lone pair of the amide nitrogen can be delocalized to the carbonyl oxygens via the π system, resulting in a zwitterionic form that increases the ability to establish hydrogen bonding interactions and consequently, the C–N bond length is shorter than usual, preventing the free rotation of the squaramide C–N bond (see Figure 4).
Another synthetic route for the preparation of mono-squaramides is the use of a microwave reactor starting from squaric acid by direct combination with an aliphatic primary amine in water [66] (see Figure 5).
It is worth noting that in addition to the acid-base properties mentioned above, squaric acid is a moderate reducing agent with a redox potential of 0.795 V. In fact, squaric acid in the presence of a HAuCl4 solution at room temperature can induce the precipitation of gold nanoparticles [67]. In short, the squaric acid moiety has very interesting acid–base and stereoelectronic properties which, together with the structural rigidity of the four-membered ring and the possibility of strict control of reactivity, make it a very interesting organic ligand for use as a building block for linking chains and forming stable one-, two-, and three-dimensional crystalline molecular frameworks [68]. The squarate dianion presents several coordination modes to numerous metal centers, as shown in Figure 6, allowing the formation of two-dimensional structures by intermolecular hydrogen bonding, which in turn can form three-dimensional structures [69].

2. Computational Details

Computations were carried out on theoretical models built using the X-ray crystallographic coordinates of the MOFs and guest molecules to unveil their interaction energy strength (see Electronic Supporting Information (ESI) for the cartesian coordinates of the computational models used). The selected structure CSD IDs follow: 2104929 [Ti2O3(SQU)], 20190731 and 20190820 [Ca(SQU)(H2O)], 1003940 ZrSQU and 2240469 Ni2Fe1 SQU-zbr. Initially, neutral MOF models were built consisting of an MOF pore, and the guest molecules and the H atoms of the system were relaxed using the density functional theory (DFT) at the PBE0 [70,71]-D3 [72]/def2-SVP [73] level of theory. In a posterior stage, these geometries were taken as starting points for single point calculations using Alrich’s basis set by means of the program TURBOMOLE version 7.7 [74]. Lastly, the interaction energies were calculated using the supermolecule approximation (ΔEMOF pore···guest complex = EMOF pore···guest complex—EMOF pore—Eguest). The interaction energies were corrected using the Boys and Bernardi counterpoise technique [75].

3. Results and Discussion

3.1. Results from the Literature Review

As a result of our literature review, we gathered in Table 1 the most relevant studies of MOFs prepared using squaramide/square ion as an organic ligand that were published over the last 20 years. It should be noted that no significant publications on this topic were found prior to 2005. Table 1 is divided into two subsections, one dedicated to squarate and the other to squaramide as the key ligands in MOF formation. Table 1 is compiled based on the MOF application, and for each application, the metal used, the empirical formula of the MOF, and the organic ligand are described. Squarate-based MOFs found in the literature are more numerous than those described with squaramide units.
Regarding MOFs built with squarate units, they have very diverse applications, depending on the final morphology acquired in relation to their components. The applications are very assorted, including the capture and separation of low molecular weight gases, with special mention to the MOF (Ti2O3)n USTC-700 that has the capacity to separate deuterium and hydrogen in a mixture of gases [76], separate gaseous alkanes, alkenes, and alkynes of the same number of carbons [28,29,77], separate nitrogen and hydrogen [78], and separate Xe and Kr [25]. Other examples focus on the capture and storage of H2 and CO2 [27,79,80], as well as in the separation of CO2 from fuel, an aspect of great industrial importance [81]. Water vapor adsorption/desorption produces changes in the structural properties of the MOF formed with squarate, manganese, and the ligand 1,2-bis(4-pyridyl)ethane [82].
Another useful capability of MOFs is their catalytic effect in several organic reactions, since MOFs show pores of specific size with very localized catalytic sites, optimal for heterogeneous catalysis. Table 1 presents several examples such as, the Michael addition reaction [83], the photocatalyst water splitting reaction [84], the transformation of tetrazines to oxadiazole derivatives [85] and the electrocatalytic oxygen evolution reaction [86,87]. In the field of supramolecular chemistry, squarate-based MOFs have been used for sensing inorganic anions (permanganate and dichromate) [88] and the neurotransmitter dopamine [89]. If biocompatible metals are used, squarate-based MOFs could potentially be used for therapeutic purposes. In 2021, an MOF based on squarate units with Ca and Sr was described that exhibits antioxidant and anticancer activity [90].
Regarding the organic ligands used, they are mostly nitrogen heterocyclic compounds such as vinyl imidazole, tetrazole, triazole, phenanthroline, pyridine, and nicotinate N-oxide, or derivatives of carbonyl acids such as oxalic, benzoic, and isophthalic acid.
In the second part of Table 1, examples of MOFs based on squaramide units are described. As can be seen, their main applications are as catalysts for organic reactions. The presence of squaramide units in the MOF results in greater structural solidity, improving reactivity and catalytic performance. Table 1 also shows three examples of catalysis reactions: the Michael addition reaction, the Friedel–Crafts reaction [91,92,93,94], and the ring opening of epoxides [95]. Finally, Table 1 is complemented by an example of the application of a luminescent sensor for the determination of lactose in water and milk [96], and the use of the Zr-MOF:UiO-68-SQ1, as a biomimetic catalyst for the transformation of small molecules [97].
The squaramide ligands used are derivatives of an aromatic carboxylic acid such as benzoic, biphenyl, or terphenyl, combined in some cases with nitrogen-containing heterocycles such as 4,4′-bipyridine or 1,2-bis(4-pyridyl)ethane).
Table 1. Squarate-based MOFs.
Table 1. Squarate-based MOFs.
Organic ligandMetalFormulaApplication
Amine fluorideZn, Co, Ni{(NH(CH3)2)2[M4F4(SQU)3]}n
(M = Zn, Co and Ni)		Separation of Acetylene from Ethylene [27]
Ca[Ca(SQU)(H2O)]Separation of Ethylene from Ethane [29]
Ca[Ca(SQU)(H2O)]Separation of CO2 from fuel gas [81]
Zr, HfMSQU
(M = Zr and Hf)		Separation of Hydrogen from Nitrogen [78]
Ca[Ca(SQU)(H2O)]Capture of trace propyne and propadiene from propylene [77]
vim = 1-vinylimidazoleCo, Zn, Cd, Ni, Cu[Co(SQU)(vim)2(H2O)2]n
[Zn(SQU)(vim)2(H2O)2]n
[Cd(SQU)(vim)2(H2O)2]n
[M(sq)(vim)2(H2O)2]n
(M = Ni and Cu)		Hydrogen storage [79,80]
ZnSQUCALF-20
[Zn2(1,2,4-triazolate)2(SQU)]		Capture of CO2 [27]
Co[Co4(OH)4(SQU)3]Separation CO2 of Nitrogen [26]
Co[Co4(OH)4(SQU)3]Separation of Xenon from Krypton [25]
CoCo3C8H2O10·2.5H2OSeparation of ethanol from trace amount water [39]
Co[Co3(OH)2(SQU)2]·3H2OReversible ferromagnetic-antiferromagnetic
[98]
Ti(Ti2O3)n USTC-700
[Ti2(μ2-O)(μ3-O)2(SQU)]		Separation of Deuterium (D2) from Hydrogen (H2) [76]
bipy = 4,4′-bipyridinCd{[Cd(SQU)(bipy)(H2O)2]·3H2O}nWater Adsorption
[24]
dpe = 1,2-bis(4-pyridyl)ethane)Mn[Mn(Hdpe)(SQU)0.5(H2O)3][Mn(SQU)2
(H2O)2] [Mn(Hdpe)2(H2O)4][Mn(SQU)2(H2O)2]2·8H2O		Water Adsorption and Magnetic applications
[82]
Fe[Fe3(OH)3(SQU)(SQU)0.5]nCO2 and CH4 Adsorption [99]
L1 = SQU-diisophthalic acid
L2 = SQU-dibenzoic acid
dpe = 1,2-di(pyridine-4-yl)ethane		CdCd2(L1)(DMF)3
Cd(L2)(dpe)		Catalyst for the Michael Addition reaction
[83]
Fe[Fe3(OH)3(SQU)(SQU)0.5]nTransformation of tetrazines to oxadiazole derivatives [85]
zbr TopologyNi, Co, FeNi2Fe1 SQU-zbrElectrocatalytic Oxygen Evolution Reaction [86,87]
Co[Co3(SQU)2(OH)2]⋅3H2O
Ti[Ti2O3(SQU)]Photocatalyst Water Splitting Reaction [84]
Tn = TetrazoleZn, Cd, Co[M(TnSQU)(H2O)3]n
(M= Zn, Cd and Co)		Photoluminescence and magnetic properties [100]
dpe = 1,2-bis(4-pyridyl)ethaneZn[Zn(dpe)(SQU)(H2O)2]n
{[Zn(Hdpe)(SQU)0.5(H2O)3][Zn(SQU)2
(H2O)2]}n		Crystal engineering of 3D-dimensional networks [101,102,103,104,105]
Eu, Am,
Cf, Sm,
Dy, Ho,
Er		M2(SQU)3(H2O)4
(M = Eu, Am and Cf)
Sm(SQU)(C4O3OH)(H2O)2·0.5H2O
[M4(SQU)5(H2O)12]Cl2·5H2O
(M = Eu, Dy, Ho and Er)
M2(SQU)2(SQU)(H2O)4
(M = Am and Cf)
Yb[Yb5(OH)6(HCO2)3(CO3)2-(SQU)] 2.5 H2O
Co[Co(SQU)4]⋅2H2O
btb = 1,4-bis(1,2,4-triazol-4-yl)butaneCd[Cd(C4O4)(btb)(H2O)2]n
(btb = 1,4-bis(1,2,4-triazol-4-yl)butane)
Nd[(CH3)2NH2Nd(SQU)2]Luminescense
Sensing MnO4−, Cr2O72− [88]
Co[Co3(SQU)2O10]⋅3H2OElectrochemical
Sensing Dopamine
[89]
Nd{(NH4)2[Nd2(H2O)10(SQU)3]SQU}nCrystal engineering of 3D-dimensional networks [106,107,108,109,110,111,112,113]
Cd[Cd(2,2′-bpe)(SQU)(H2O)2] (2,2′-bpe =
1,2-bis(2-pyridyl)ethylene)
NNO = nicotinate N-oxideDy[Dy(NNO)(SQU)(H2O)]n
bpe = 1,2-bis(4-pyridyl)ethane.
phen = 1,10-phenanthroline		Mn{[Mn(H2O)2(bpe)(SQU)]·bpe·H2O}n
[Mn2(H2O)4(phen)2(SQU2)]n
[Mn2(H2O)2(phen)4(SQU)]·(SQU)·8(H2O)
Cd[Cd(SQU)(H2O)2]n
Co, Mn, ZnCo(H2O)2(SQU)
Mn(H2O)2(SQU)
Zn(H2O)2(SQU)
SODALITE
dpa = 2,2′-dipyridylamineCo, Ni, Zn, Cu[M(dpa)(SQU)H2O)]
(M = Co, Ni, Zn)
[Cu(dpa)(SQU)(H2O)]2·H2O
dpa = 2,2′-dipyridylamineCd[Cd2(SQU)2.5(H2O)4](dpaH)·1.5(H2O)
[Cd(SQU)(dpa)(H2O)]
(dpa= 2,2′-dipyridylamine)
Sr, Ca[Sr0.88Ca 0.12(SQU)(H2O)3]Antioxidant and Anticancer Activities [90]
bpy = 4,4′-bipyridine
bpydo = 4,4′-bipyridine-N,N′-dioxide
phen= 1,10-phenanthroline
OA= Oxalic acid.
vidpy = 4,4′-vinylenedipyridine		U[(UO2)(OH)(SQU)](Hbpy)
(UO2)(H2O)(SQU)(bpydo)·2H2O
(UO2)(H2O)(SQU)(phen)·H2O
[(UO2)(SQU)(OA)0.5](Hvidpy)		Structure Regulation and
Redox Activity [114]
OA= Oxalic acidHo[Ho2(AO)(SQU)2(H2O)8]·4(H2O)
[Ho(SQU)1.5(H2O)3]		Photo-Induced Color-Changing [115]
dbda = 3,3′-((3,4-dioxocyclobut-1-ene-1,2-diyl)bis(azanediyl))dibenzoic acidZn{Zn1.5(OH)(dbda)·5DMF}n
squaramide		Catalyst for the Michael Addition reaction
[116]
bdpc = 4,4′-biphenyldicarboxylateZrZr6O4(OH)4(Squar)2(bpdc)2Catalyst for the Friedel–Crafts reaction [91,92,93,94]
dbda = N,N’-bis(3,5-dicarboxyphenyl)squaramide
tptc = p-terphenyl-3,3″,5,5″-tetracarboxylic acid		Cu[Cu2(dbda)]
[Cu2(dbda)x(tptc)1-x]
Sq_tpdc = 4,4′-((3,4-dioxocyclobut-1-ene-1,2-
diyl)bis(azanediyl))dibenzoic acid		Zn, ZrSq_tpdc
(Sq_IRMOF-16)
(Sq_UiO-68)
Sq_tpdc = 4,4′-((3,4-dioxocyclobut-1-ene-1,2-
diyl)bis(azanediyl))dibenzoic acid
4,4′-bipyridine		ZnSq_SNU-8X
Sq_tpdc = 4,4′-((3,4-dioxocyclobut-1-ene-1,2-
diyl)bis(azanediyl))dibenzoic acid
1,2-bis(4-pyridyl) ethane		ZrSq_BptMOF
3,4-dioxocyclobut-1-ene-1,2-diyl)bis(azanedyil)-p-dibenzoic acidZnSq_IRMOF-16Catalyst for epoxide ring-opening reaction [95]
bpy = 4,4′-bipyridine
dbda = 3,3′-((3,4-dioxocyclobut-1-ene-1,2-diyl)bis(azanediyl))dibenzoic acid		CoCo(bpy)(dbda)·H2OLuminescense
Sensing [96]
SQ1 = 3,3′-((3,4-dioxocyclobut-1-ene-1,2-diyl)bis(phenylbenzoic) acidZrUiO-68-SQ1Biomimetic
Catalysts [97]

3.2. Selected Squarate-Based MOF Examples

From the results presented above, we selected several MOFs based on squarate that have been used as (i) efficient photocatalysts, (ii) gas adsorbents, and (iii) water collectors, owing to their impact in environmental and material science fields. This was mainly due to (i) the higher abundance of squarate-based MOFs compared to squaramide-based ones, and (ii) the presence of X-ray crystal structures including guest molecules trapped inside the MOF structure, thus allowing us to computationally investigate the stability of supramolecular MOF–guest complexes and the noncovalent interactions involved.
The first selected example corresponds to the work from Salcedo-Abraira and collaborators [78], who proposed a novel Ti-squarate MOF as a photocatalyst for the overall water splitting reaction. This titanium (IV) squarate MOF, designated as IEF-11, was synthesized solvothermally using a high-throughput approach [69]. Specifically, the authors achieved high yields of pure IEF-11 by heating a combination of squaric acid and titanium butoxide in a solvent mixture of glacial acetic acid and isopropanol at 120 °C for three days. They emphasized the material’s photocatalytic capabilities for both H2 generation and overall water splitting under simulated sunlight irradiation, demonstrating its potential for developing innovative and efficient photocatalytic hybrid materials.
After applying such reaction conditions, the authors observed the formation of small nanometric crystals exhibiting a hexagonal geometry and elucidated their 3D structure by single crystal X-ray diffraction. Interestingly, in the solid state architecture of IEF-11 there were both O6 and water molecules interacting with the squarate MOF walls, as can be observed in Figure 7. More in detail, the O6 ring and water molecules seemed to be stabilized by the formation of O···O contacts (likely of dispersive nature) with an O···O distance of 2.844 Å and O···H hydrogen bonding interactions, with an O···H distance of 2.331 Å, respectively. A theoretical model of the interaction between a captured water molecule and the IEF-11 porous was built (see ESI for the cartesian coordinates), showing an interaction energy strength of −0.9 kcal/mol, which corresponds to a weak hydrogen bond energy [117], thus contributing to the stabilization of this guest molecule during the photocatalytic process.
The second selected example corresponds to the study from Li and coworkers [77], where they synthesized and characterized a Ca-based MOF using squarate as organic ligand for the simultaneous capturing of propyne and propadiene from propylene. Propylene is the second most-produced hydrocarbon globally, following ethylene. It is widely used as a chemical feedstock for manufacturing various products, including polypropylene plastics, copolymers, and propylene oxide [118,119]. The primary method of propylene production involves steam and/or catalytic cracking of larger hydrocarbons. However, this process inevitably generates undesirable impurities such as propyne and propadiene, which can deactivate the catalyst used in propylene polymerization. Therefore, their removal from crude propylene streams is crucial for producing polymer-grade propylene.
From a synthetic point of view, the authors obtained this compound by mixing CaCO3 and squaric acid in 20 mL of deionized water using a 25 mL Teflon-lined reactor. The reactor was then heated to 393 K for 24 h, followed by gradual cooling over several hours. The resulting white, rod-like crystals were collected via centrifugation and subsequently washed multiple times with deionized water.
In the MOF solid state structure (see Figure 8), the propadiene and propyne molecules were trapped traversing the MOF pores and interacting with the π-systems belonging to the squarate moieties, establishing π–π and CH–π interactions, with intermolecular distances comprised between 3.3 and 3.6 Å in the case of propadiene and between 3.4 and 3.8 Å in the case of propyne. The interaction energies for each supramolecular complex were obtained, resulting in −12.9 kcal/mol in the case of the MOF–propadiene complex and −11.9 kcal/mol in the case of the MOF–propyne complex, denoting the moderately strong nature of these π–π and CH–π contacts in the capturing process of these two compounds. These results are in line with those previously obtained by us [120] and other groups, such as the work from Ran and collaborators [121], who estimated the strength of hydrocarbon–π-system complexes.
The third example corresponds to the work from Bueken and collaborators [78], where they reported the first zirconium squaric acid-based MOF. In summary, this solid was synthesized by reacting squaric acid with ZrCl4 in a mixture of dimethylformamide (DMF), aqueous HCl, and a monocarboxylic acid modulator (either acetic acid or formic acid) at 110 °C for 2 h. As with other known Zr-MOFs, the presence of a modulator was essential for obtaining a crystalline material. Additionally, the authors increased the concentrations of HCl and the modulator during synthesis, which further improved the crystallinity of the final product.
The structure of Zr MOF was solved from powder X-ray diffraction, featuring both octahedral and tetrahedral cages with diameters of 5.6 Å and 4.7 Å, respectively, enclosed by triangular windows. Interestingly, the authors also crystallized an isostructural Hf-analogue by replacing ZrCl4 with equimolar amounts of HfCl4. The solid state structure of both MOFs showed four O3 molecules adsorbed inside (see Figure 9), exhibiting a tetrahedral distribution. These ozone molecules were located very close to each other inside the MOF pore (showing intermolecular distances of around 1.7 Å) and, therefore, were forced to adopt a triangular disposition instead of the typical bent geometry. We modeled the interaction between the Zr-MOF pore and the four O3 molecules, which was mainly based on the establishment of several lone pair–π interactions, resulting in an interaction energy strength of −32.9 kcal/mol per O3 molecule.
The last selected example corresponds to the study from Kandambeth and collaborators [83], where they synthesized a bimetallic Co/Ni/Fe squarate-based MOF for the study of the electrocatalytic oxygen evolution reaction (OER). During the synthetic procedure, the bimetallic Co-Ni, Ni-Fe, Co-Fe MOFs were obtained in a 100 mL Teflon-lined reactor under hydrothermal reaction conditions at 220 °C. After the reaction, these squarate MOFs were purified using deionized water and acetone.
The authors conducted various experimental studies, including cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements, backed up by theoretical calculations. Their findings revealed that controlling the Ni2+ content in the bimetallic MOF system was crucial for ensuring electrochemical structural stability during the OER. Notably, one of the tested compounds (Ni2Fe1 Sq-zbr-MOF) outperformed the commercially available noble-metal-based RuO2 catalysts for the OER under identical conditions, thus demonstrating that chemically robust MOFs with metal hydroxide chains can serve as a promising structural alternative to metal hydroxides and metal oxides in electrocatalysis.
The bimetallic squarate MOFs studied by the authors were obtained as single crystals with varying colors depending on metal ratios: from magenta to green (Co–Ni, from green to yellow (Fe–Ni), and from red to magenta (Co–Fe). Single crystal X-ray diffraction and powder X-ray diffraction (PXRD) analyses were used to determine their crystal structures. In their solid state, several O2 were trapped inside the MOF pores, establishing lone pair–π interactions between the oxygen lone pairs and the π-system of the squarate molecules, with intermolecular distances comprised between 3.2 and 3.5 Å (see Figure 10). We computed the interaction energy between the Ni–Fe MOF and the four O2 molecules trapped inside, resulting in −77.8 kcal/mol per O2 molecule, thus marking the importance of these supramolecular contacts for stabilization of the O2 molecules inside the MOF structure [122].
To summarize the main data from calculations, we gathered the molecular formula, the total energies of MOF and its corresponding fragments, the electronic multiplicity of each metal atom, as well as the counterpoise corrected interaction energy values in Table 2. In addition, each type of noncovalent bond involved in the formation of these MOF–guest supramolecular complexes was also included, to give an overview of the different weak forces that are responsible for the interaction between the MOF pore and the reactants/products or guests trapped inside. These include O···H hydrogen bonds involving a guest water molecule, CH–π and π–π interactions involving unsaturated hydrocarbon molecules as well as O···C lone pair–π interactions involving O3 and O2 molecules.

4. Conclusions

In this review, we highlighted the potential use of squaramide- and squarate-based MOFs for a wide range of chemical, environmental, and energetic applications, such as gas separation, gas capture, formation of 3D crystal networks, and even antioxidant and anticancer activities. In addition, some selected examples were described in more detail, including the theoretical evaluation of the NCIs involved in the formation of supramolecular MOF–guest complexes. We believe that the examples gathered herein will be useful for those scientists working in the fields of supramolecular chemistry, crystal engineering, catalysis, and materials science by providing a retrospective guide on the role of squaramide and squarate as MOF organic ligands.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst15040294/s1, Cartesian coordinates of the theoretical models used.

Author Contributions

Conceptualization, J.M. and A.B.; methodology, J.M. and A.B.; investigation, C.N., M.d.l.N.P., J.M. and A.B.; writing—original draft preparation, J.M. and A.B.; writing—review and editing, J.M. and A.B.; supervision, J.M. and A.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by MICIU/AEI, PID2020-115637GB-I00 FEDER funds.

Data Availability Statement

The data needed to reproduce the results derived from this work can be found in the Supplementary Materials.

Acknowledgments

All authors thank the MICIU/AEI for financial support (PID2020-115637GB-I00 FEDER funds). The authors thank the CTI (UIB) for computational facilities.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
CVCyclic voltammetry
DFTDensity functional theory
LSVLinear sweep voltammetry
MOFMetal–organic framework
NCIsNoncovalent interactions
OEROxygen evolution reaction
PXRDPowder X-ray diffraction
SBUSecondary building unit
VOCVolatile organic compound

References

  1. Yaghi, O.M.; Li, G.; Li, H. Selective binding and removal of guests in a microporous metal–organic framework. Nature 1995, 378, 703–706. [Google Scholar]
  2. Cook, T.R.; Zheng, Y.R.; Stang, P.J. Metal-organic frameworks and self-assembled supramolecular coordination complexes: Comparing and contrasting the design, synthesis, and functionality of metal-organic materials. Chem. Rev. 2013, 113, 734–777. [Google Scholar] [PubMed]
  3. Kirchon, A.; Feng, L.; Drake, H.F.; Joseph, E.A.; Zhou, H.C. From fundamentals to applications: A toolbox for robust and multifunctional MOF materials. Chem. Soc. Rev. 2018, 47, 8611–8638. [Google Scholar]
  4. Gao, J.; Qian, X.; Lin, R.B.; Krishna, R.; Wu, H.; Zhou, W.; Chen, B. Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation. Angew. Chem. Int. Ed. 2020, 59, 4396–4400. [Google Scholar] [CrossRef]
  5. Li, M.; Guo, Y.; Yang, J. Spatially Nanoconfined Architectures: A Promising Design for Selective Catalytic Reduction of NOx. ChemCatChem 2020, 12, 5599–5610. [Google Scholar] [CrossRef]
  6. Guo, J.; Qin, Y.; Zhu, Y.; Zhang, X.; Long, C.; Zhao, M.; Tang, Z. Metal–organic frameworks as catalytic selectivity regulators for organic transformations. Chem. Soc. Rev. 2021, 50, 5366–5396. [Google Scholar] [CrossRef]
  7. Lawson, H.D.; Walton, P.; Chan, C. Metal–Organic Frameworks for Drug Delivery: A Design Perspective. ACS Appl. Mater. Interfaces 2021, 13, 7004–7020. [Google Scholar]
  8. Zheng, Y.; Sun, F.-Z.; Han, X.; Xu, J.; Bu, X.-H. Recent Progress in 2D Metal-Organic Frameworks for Optical Applications. Adv. Opt. Mater. 2020, 8, 2000110. [Google Scholar]
  9. Ren, J.; Langmi, H.W.; North, B.C.; Mathe, M. Review on processing of metal–organic framework (MOF) materials towards system integration for hydrogen storage. Int. J. Energy Res. 2015, 39, 607–620. [Google Scholar]
  10. Ma, X.; Chai, Y.; Wang, B. Metal–Organic Framework Films and Their Potential Applications in Environmental Pollution Control. Acc. Chem. Res. 2019, 52, 1461–1470. [Google Scholar]
  11. Hu, M.-L.; Safarifard, V.; Doustkhah, E.; Rostamnia, S.; Morsali, A.; Nouruzi, N.; Beheshti, S.; Akhbari, K. Taking organic reactions over metal-organic frameworks as heterogeneous catalysis. Microporus Mesoporus Mater. 2018, 256, 111–127. [Google Scholar]
  12. Qian, Z.; Zhang, R.; Xiao, Y.; Huang, H.; Sun, Y.; Chen, Y.; Ma, T.; Sun, X. Trace to the Source: Self-Tuning of MOF Photocatalysts. Adv. Energy Mater. 2023, 13, 2300086. [Google Scholar]
  13. Liu, J.; Zhu, D.; Guo, C.; Vasileff, A.; Qiao, S.-Z. Design Strategies toward Advanced MOF-Derived Electrocatalysts for Energy-Conversion Reactions. Adv. Energy Mater. 2017, 7, 1700518. [Google Scholar]
  14. Pobłocki, K.; Drzeżdżon, J.; Gawdzik, B.; Jacewicz, D. Latest trends in the large-scale production of MOFs in accordance with the principles of green chemistry. Green Chem. 2022, 24, 9402–9427. [Google Scholar]
  15. Sabzehmeidani, M.M.; Gafari, S.; Jamali, S.; Kazemzad, M. Concepts, fabrication and applications of MOF thin films in optoelectronics: A review. Appl. Mater. Today 2024, 38, 102153. [Google Scholar]
  16. Paz, F.A.A.; Klinowski, J.; Vilela, S.M.F.; Tomé, J.P.C.; Cavaleiro, J.A.S.; Rocha, J. Ligand design for functional metal–organic frameworks. Chem. Soc. Rev. 2012, 41, 1088–1110. [Google Scholar]
  17. Chen, T.H.; Popov, I.; Kaveevivitchai, W.; Miljanić, O.Š. Metal-organic frameworks: Rise of the ligands. Chem. Mater. 2014, 26, 4322–4325. [Google Scholar]
  18. Lin, Z.J.; Lü, J.; Hong, M.; Cao, R. Metal–organic frameworks based on flexible ligands (FL-MOFs): Structures and applications. Chem. Soc. Rev. 2014, 43, 5867–5895. [Google Scholar]
  19. Zhang, L.P.; Yang, J.; Ma, J.F.; Jia, Z.F.; Xie, Y.P.; Wei, G.H. A series of 2D and 3D metal–organic frameworks based on different polycarboxylate anions and a flexible 2,2′-bis(1H-imidazolyl)ether ligand. CrystEngComm 2008, 10, 1410–1420. [Google Scholar]
  20. Wang, C.; Zhao, J.; Xia, L.; Wu, X.Q.; Wang, J.F.; Dong, W.W.; Wu, Y.P. Utilization of mixed ligands to construct diverse Ni(II)-coordination polymers based on terphenyl-2,2′,4,4′-tetracarboxylic acid and varied N-donor co-ligands. J. Solid State Chem. 2016, 238, 273–278. [Google Scholar]
  21. Ghassa, M.; Khorashe, F.; Hajjar, Z.; Soltanali, S. Comparative Study on Adsorptive Desulfurization of Thiophenic Compounds over Terephthalic Acid-Based and Trimesic Acid-Based Metal–Organic Frameworks. Energy Fuels 2023, 37, 6490–6502. [Google Scholar] [CrossRef]
  22. Zhao, Y.; Chai, Y.-H.; Ding, L.; Wang, S.; Wang, Y.-N.; Ma, L.-F.; Zhao, B.-T. A stable N-containing heterocyclic carboxylic acid ligand Co-MOF for photoelectric performance and anionic dyes adsorption. Arab. J. Chem. 2023, 16, 104878. [Google Scholar] [CrossRef]
  23. Pullen, S.; Clever, G.H. Mixed-Ligand Metal–Organic Frameworks and Heteroleptic Coordination Cages as Multifunctional Scaffolds—A Comparison. Acc. Chem. Res. 2018, 51, 3052–3064. [Google Scholar] [CrossRef] [PubMed]
  24. Wang, C.-C.; Ke, S.-Y.; Chen, K.-T.; Hsieh, Y.-F.; Wang, T.-H.; Lee, G.-H.; Chuang, Y.-C. Reversible Single-Crystal-to-Single-Crystal Structural Transformation in a Mixed-Ligand 2D Layered Metal-Organic Framework: Structural Characterization and Sorption Study. Crystals 2017, 7, 364. [Google Scholar] [CrossRef]
  25. Li, L.; Guo, L.; Zhang, Z.; Yang, Q.; Yang, Y.; Bao, Z.; Ren, Q.; Li, J. A Robust Squarate-Based Metal-Organic Framework Demonstrates Record-High Affinity and Selectivity for Xenon over Krypton. J. Am. Chem. Soc. 2019, 141, 9358–9364. [Google Scholar] [CrossRef]
  26. Zhang, L.; He, Z.; Liu, Y.; You, J.; Lin, L.; Jia, J.; Chen, S.; Hua, N.; Ma, L.A.; Ye, X.; et al. A Robust Squarate-Cobalt Metal-Organic Framework for CO2/N2 Separation. ACS Appl. Mater. Interfaces 2023, 15, 30394–30401. [Google Scholar] [CrossRef]
  27. Gopalsamy, K.; Fan, D.; Naskar, S.; Magnin, Y.; Maurin, G. Engineering of an Isoreticular Series of CALF-20 Metal–Organic Frameworks for CO2 Capture. ACS Appl. Eng. Mater. 2024, 2, 96–103. [Google Scholar] [CrossRef]
  28. Li, H.P.; Wang, J.W.; Zhai, Q.G. Development of MOF-5-like ultra-microporous metal-squarate frameworks for efficient acetylene storage and separation. J. Mater. Chem. A 2023, 11, 21203–21210. [Google Scholar] [CrossRef]
  29. Lin, R.B.; Li, L.; Zhou, H.L.; Wu, H.; He, C.; Li, S.; Krishna, R.; Li, J.; Zhou, W.; Chen, B. Molecular sieving of ethylene from ethane using a rigid metal–organic framework. Nat. Mater. 2018, 17, 1128–1133. [Google Scholar]
  30. Arici, M.; Yesilel, O.Z.; Tas, M.; Demiral, H. Effect of Solvent Molecule in Pore for Flexible Porous Coordination Polymer upon Gas Adsorption and Iodine Encapsulation. Inorg. Chem. 2015, 54, 11283–11291. [Google Scholar] [CrossRef]
  31. Cao, J.; Li, X.; Tian, H. Metal-Organic Framework (MOF)-Based Drug Delivery. Curr. Med. Chem. 2019, 27, 5949–5969. [Google Scholar] [CrossRef] [PubMed]
  32. Cai, M.; Chen, G.; Qin, L.; Qu, C.; Dong, X.; Ni, J.; Yin, X. Metal Organic Frameworks as Drug Targeting Delivery Vehicles in the Treatment of Cancer. Pharmaceutics 2020, 12, 232. [Google Scholar] [CrossRef]
  33. Zeng, L.W.; Hu, K.Q.; Mei, L.; Li, F.Z.; Huang, Z.W.; An, S.W.; Chai, Z.F.; Shi, W.Q. Structural Diversity of Bipyridinium-Based Uranyl Coordination Polymers: Synthesis, Characterization, and Ion-Exchange Application. Inorg. Chem. 2019, 58, 14075–14084. [Google Scholar] [CrossRef] [PubMed]
  34. Zhao, L.M.; Li, H.H.; Wu, Y.; Zhang, S.Y.; Zhang, Z.J.; Shi, W.; Cheng, P.; Liao, D.Z.; Yan, S.P. Synthesis, Crystal Structures, and Magnetic Properties of Mn(II), Co(II), and Zn(II) Coordination Polymers Containing 1,2,4,5-Benzenetetracarboxylic Acid and 4,4’-Azobispyridine. Eur. J. Inorg. Chem. 2010, 2010, 1983–1990. [Google Scholar] [CrossRef]
  35. Wang, Q.; Astruc, D. State of the Art and Prospects in Metal-Organic Framework (MOF)-Based and MOF-Derived Nanocatalysis. Chem. Rev. 2020, 120, 1438–1511. [Google Scholar] [CrossRef]
  36. Zhou, Z.; Mukherjee, S.; Hou, S.; Li, W.; Elsner, M.; Fischer, R.A. Porphyrinic MOF Film for Multifaceted Electrochemical Sensing. Angew. Chem. Int. Ed. 2021, 60, 20551–20557. [Google Scholar] [CrossRef]
  37. Stavila, V.; Talin, A.A.; Allendorf, M.D. MOF-based electronic and opto-electronic devices. Chem. Soc. Rev. 2015, 43, 5994–6010. [Google Scholar] [CrossRef]
  38. Wang, J.; Yuan, F.; Hu, H.M.; Xu, B.; Xue, G.L. A luminescent coordination polymer with potential active site for the sensing of metal cation, anion and nitrobenzene explosive. Inorg. Chem. Commun. 2016, 71, 19–22. [Google Scholar] [CrossRef]
  39. Zheng, X.; Chen, L.; Zhang, H.; Yao, Z.; Yang, Y.; Xiang, F.; Li, Y.; Xiang, S.; Zhang, Z.; Chen, B. Optimized Sieving Effect for Ethanol/Water Separation by Ultramicroporous MOFs. Angew. Chem. Int. Ed. 2023, 62, e202216710. [Google Scholar] [CrossRef]
  40. Li, J.R.; Kuppler, R.J.; Zhou, H.C. Selective gas adsorption and separation in metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1477–1504. [Google Scholar] [CrossRef]
  41. Zhou, Z.; Vázquez-González, M.; Willner, I. Stimuli-responsive metal-organic framework nanoparticles for controlled drug delivery and medical applications. Chem. Soc. Rev. 2021, 50, 4541–4563. [Google Scholar] [PubMed]
  42. Linnane, E.; Haddad, S.; Melle, F.; Mei, Z.; Fairen-Jimenez, D. The uptake of metal-organic frameworks: A journey into the cell. Chem. Soc. Rev. 2022, 51, 6065–6086. [Google Scholar] [PubMed]
  43. Horcajada, P.; Tamim, C.; Serre, C.; Gillet, B.; Sébrié, C.; Baati, T.; Eubank, J.; Heurtaux, D.; Clayette, P.; Kreuz, C.; et al. Porous metal-organic-framework nanoscale carriers as a potential platform for drug delivery and imaging. Nat. Mater. 2010, 9, 172–178. [Google Scholar] [PubMed]
  44. Rojas, S.; Arenas-Vivo, A.; Horcajada, P. Metal-organic frameworks: A novel platform for combined advanced therapies. Coord. Chem. Rev. 2019, 388, 202–226. [Google Scholar]
  45. Liu, J.; Huang, J.; Zhang, L.; Lei, J. Multifunctional metal–organic framework heterostructures for enhanced cancer therapy. Chem. Soc. Rev. 2021, 50, 1188–1218. [Google Scholar]
  46. Han, D.; Liu, X.; Wu, S. Metal organic framework-based antibacterial agents and their underlying mechanisms. Chem. Soc. Rev. 2022, 51, 7138–7169. [Google Scholar]
  47. Huang, S.; Chen, G.; Ouyang, G. Confining enzymes in porous organic frameworks: From synthetic strategy and characterization to healthcare applications. Chem. Soc. Rev. 2022, 51, 6824–6863. [Google Scholar]
  48. Zheng, Q.; Liu, X.; Zheng, Y.; Yeung, K.W.K.; Cui, Z.; Liang, Y.; Li, Z.; Zhu, S.; Wang, X.; Wu, S. The recent progress on metal–organic frameworks for phototherapy. Chem. Soc. Rev. 2021, 50, 5086–5125. [Google Scholar]
  49. Yao, H.; Cai, S.; Yang, B.; Han, L.; Wang, P.; Li, H.; Yan, T.; Shi, L.; Zhang, D. In situ decorated MOF-derived Mn–Fe oxides on Fe mesh as novel monolithic catalysts for NOx reduction. New J. Chem. 2020, 44, 2357–2366. [Google Scholar]
  50. Zhang, X.; Chen, Z.; Liu, X.; Hanna, S.L.; Wang, X.; Taheri-Ledari, R.; Maleki, A.; Li, P.; Farha, O.K. A historical overview of the activation and porosity of metal–organic frameworks. Chem. Soc. Rev. 2020, 49, 7406–7427. [Google Scholar]
  51. Suresh, K.; Kalenak, A.P.; Sotuyo, A.; Matzger, A.J. Metal-Organic Framework (MOF) Morphology Control by Design. Chem. Eur. J. 2022, 28, e202200334. [Google Scholar] [CrossRef] [PubMed]
  52. Yang, L.; Qian, S.; Wang, X.; Cui, X.; Chen, B.; Xing, H. Energy-efficient separation alternatives: Metal–organic frameworks and membranes for hydrocarbon separation. Chem. Soc. Rev. 2020, 49, 5359–5406. [Google Scholar] [CrossRef] [PubMed]
  53. Cheng, Y.; Datta, S.J.; Zhou, S.; Jia, J.; Shekhah, O.; Eddaoudi, M. Advances in metal–organic framework-based membranes. Chem. Soc. Rev. 2022, 51, 8300–8350. [Google Scholar] [CrossRef]
  54. Zhang, X.; Maddock, J.; Nenoff, T.M.; Denecke, M.A.; Yang, S.; Schröder, M. Adsorption of iodine in metal–organic framework materials. Chem. Soc. Rev. 2022, 51, 3243–3262. [Google Scholar] [CrossRef]
  55. Li, H.Y.; Zhao, S.N.; Zang, S.Q.; Li, J. Functional metal–organic frameworks as effective sensors of gases and volatile compounds. Chem. Soc. Rev. 2020, 49, 6364–6401. [Google Scholar] [CrossRef]
  56. Adjal, C.; Guechtouli, N.; Timón, V.; Colmenero, F.; Hammoutène, D. Theoretical Study of Copper Squarate as a Promising Adsorbent for Small Gases Pollutants. Molecules 2024, 29, 3140. [Google Scholar] [CrossRef]
  57. Abánades Lázaro, I.; Haddad, S.; Rodrigo-Muñoz, J.M.; Marshall, R.J.; Sastre, B.; del Pozo, V.; Fairen-Jimenez, D.; Forgan, R.S. Surface-Functionalization of Zr-Fumarate MOF for Selective Cytotoxicity and Immune System Compatibility in Nanoscale Drug Delivery. ACS Appl. Mater. Interfaces 2018, 10, 31146–31157. [Google Scholar] [CrossRef]
  58. Eddaoudi, M.; Moler, D.B.; Li, H.; Chen, B.; Reineke, T.M.; O’Keeffe, M.; Yaghi, O.M. Modular Chemistry:  Secondary Building Units as a Basis for the Design of Highly Porous and Robust Metal−Organic Carboxylate Frameworks. Acc. Chem. Res. 2001, 34, 319–330. [Google Scholar]
  59. Alqadami, A.A.; Naushad, M.; Alothman, Z.A.; Ghfar, A.A. Novel Metal–Organic Framework (MOF) Based Composite Material for the Sequestration of U(VI) and Th(IV) Metal Ions from Aqueous Environment. ACS Appl. Mater. Interfaces 2017, 9, 36026–36037. [Google Scholar] [CrossRef]
  60. Kalaj, M.; Bentz, K.C.; Ayala, S., Jr.; Palomba, J.M.; Barcus, K.S.; Katayama, Y.; Cohen, S.M. MOF-Polymer Hybrid Materials: From Simple Composites to Tailored Architectures. Chem. Rev. 2020, 16, 8267–8302. [Google Scholar] [CrossRef]
  61. Cohen, S.; Cohen, S.G. Preparation and Reactions of Derivatives of Squaric Acid. Alkoxy-, Hydroxy-, and Aminocyclobutenediones1. J. Am. Chem. Soc. 1966, 88, 1533–1536. [Google Scholar] [CrossRef]
  62. Ito, M.; West, R. New Aromatic Anions. IV. Vibrational Spectra and Force Constants for C4O4−2 and C5O5−2. J. Am. Chem. Soc. 1963, 85, 2580–2584. [Google Scholar] [CrossRef]
  63. Quiñonero, D.; Frontera, A.; Ballester, P.; Deyà, P.M. A theoretical study of aromaticity in squaramide and oxocarbons. Tetrahedron Lett. 2000, 41, 2001–2005. [Google Scholar] [CrossRef]
  64. Storer, R.I.; Aciro, C.; Jones, L.H. Squaramides: Physical properties, synthesis and applications. Chem. Soc. Rev. 2011, 40, 2330–2346. [Google Scholar] [CrossRef]
  65. Frontera, A.; Orell, M.; Garau, C.; Quiñonero, D.; Molins, E.; Mata, I.; Morey, J. Preparation, solid-state characterization, and computational study of a crown ether attached to a squaramide. Org. Lett. 2005, 7, 1437–1440. [Google Scholar] [CrossRef]
  66. Rostami, A.; Colin, A.; Li, X.Y.; Chudzinski, M.G.; Lough, A.J.; Taylor, M.S. N,N′-Diarylsquaramides: General, high-yielding synthesis and applications in colorimetric anion sensing. J. Org. Chem. 2010, 75, 3983–3992. [Google Scholar] [CrossRef]
  67. López, C.; Vega, M.; Sanna, E.; Rotger, C.; Costa, A. Efficient microwave-assisted preparation of squaric acid monoamides in water. RSC Adv. 2013, 3, 7249–7253. [Google Scholar] [CrossRef]
  68. Larm, N.E.; Essner, J.B.; Pokpas, K.; Canon, J.A.; Jahed, N.; Iwuoha, E.I.; Baker, G.A. Room-Temperature Turkevich Method: Formation of Gold Nanoparticles at the Speed of Mixing Using Cyclic Oxocarbon Reducing Agents. J. Phy. Chem. C 2018, 122, 5105–5118. [Google Scholar] [CrossRef]
  69. Adamo, C.; Barone, V. Toward reliable density functional methods without adjustable parameters: The PBE0 model. J. Chem. Phys. 1999, 110, 6158. [Google Scholar] [CrossRef]
  70. Ernzerhof, M.; Scuseria, G.E. Assessment of the Perdew–Burke–Ernzerhof exchange-correlation functional. J. Chem. Phys. 1999, 110, 5029. [Google Scholar] [CrossRef]
  71. Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104. [Google Scholar] [CrossRef] [PubMed]
  72. Schäfer, A.; Horn, H.; Ahlrichs, R. Fully optimized contracted Gaussian basis sets for atoms Li to Kr. J. Chem. Phys. 1992, 97, 2571. [Google Scholar] [CrossRef]
  73. Balasubramani, S.G.; Chen, G.P.; Coriani, S.; Diedenhofen, M.; Frank, M.S.; Franzke, Y.J.; Furche, F.; Grotjahn, R.; Harding, M.E.; Hättig, C.; et al. TURBOMOLE: Modular program suite for ab initio quantum-chemical and condensed-matter simulations. J. Chem. Phys. 2020, 152, 184107. [Google Scholar] [CrossRef] [PubMed]
  74. Boys, S.F.; Bernardi, F. The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol. Phys. 1970, 19, 553. [Google Scholar] [CrossRef]
  75. Mamidi, N.; Delgadillo, R.M.V. Squaramide-Immobilized Carbon Nanoparticles for Rapid and High-Efficiency Elimination of Anthropogenic Mercury Ions from Aquatic Systems. ACS Appl. Mater. Interfaces 2022, 14, 35789–35801. [Google Scholar] [CrossRef]
  76. Yan, Q.; Wang, J.; Zhang, L.; Liu, J.; Wahiduzzaman, M.; Yan, N.; Yu, L.; Dupuis, R.; Wang, H.; Maurin, G.; et al. A squarate-pillared titanium oxide quantum sieve towards practical hydrogen isotope separation. Nat. Commun. 2023, 14, 4189. [Google Scholar] [CrossRef]
  77. Li, L.; Guo, L.; Zheng, F.; Zhang, Z.; Yang, Q.; Yang, Y.; Ren, Q.; Bao, Z. Calcium-Based Metal-Organic Framework for Simultaneous Capture of Trace Propyne and Propadiene from Propylene. ACS Appl. Mater. Interfaces 2020, 12, 17147–17154. [Google Scholar] [CrossRef]
  78. Bueken, B.; Reinsch, H.; Reimer, N.; Stassen, I.; Vermoortele, F.; Ameloot, R.; Stock, N.; Kirschhock, C.E.A.; De Vos, D. A zirconium squarate metal–organic framework with modulator-dependent molecular sieving properties. Chem. Commun. 2014, 50, 10055–10058. [Google Scholar] [CrossRef]
  79. Yilmaz, H.; Andac, O.; Gorduk, S. Synthesis, characterization, and hydrogen storage capacities of polymeric squaric acid complexes containing 1-vinylimidazole. Polyhedron 2017, 133, 16–23. [Google Scholar] [CrossRef]
  80. Yilmaz, H.; Gorduk, S.; Andac, O. Polymeric Ni(II) and Cu(II) complexes based on squaric acid and 1-vinylimidazole: Structural studies and hydrogen adsorption properties. Inorganica Chim. Acta 2018, 469, 154–163. [Google Scholar] [CrossRef]
  81. Tu, R.; Zhang, W.; Zhang, J.; Wang, M.; Zhang, F.; Yang, K.; Li, J.; Pan, H.; Bernards, M.T.; Xie, P.; et al. Squarate-Calcium Metal-Organic Framework for Molecular Sieving of CO2 from Flue Gas with High Water Vapor Resistance. Energy Fuels 2021, 35, 13900–13907. [Google Scholar] [CrossRef]
  82. Wang, C.C.; Tsai, J.H.; Ke, S.Y.; Lee, G.H.; Chuang, Y.C.; Yang, E.C. Structural Characterization, Water Adsorption, and Magnetic Properties of Two Composite Mn(II)-Squarate-dpe Supramolecular Architectures. Cryst. Growth Des. 2020, 20, 5395–5405. [Google Scholar] [CrossRef]
  83. Liu, Y.; Ma, J.; Wu, P.; Zheng, J.J.; Tian, X.; Jiang, M.; He, Y.; Dong, H.; Wang, J. A nanoporous metal–organic framework as a renewable size-selective hydrogen-bonding catalyst in water. Dalton Trans. 2019, 48, 11855–11861. [Google Scholar] [CrossRef] [PubMed]
  84. Salcedo-Abraira, P.; Babaryk, A.A.; Montero-Lanzuela, E.; Contreras-Almengor, O.R.; Cabrero-Antonino, M.; Grape, E.S.; Willhammar, T.; Navalón, S.; Elkäim, E.; García, H.; et al. A Novel Porous Ti-Squarate as Efficient Photocatalyst in the Overall Water Splitting Reaction under Simulated Sunlight Irradiation. Adv. Mater. 2021, 33, 2106627. [Google Scholar] [CrossRef]
  85. Goswami, S.; Jena, H.S.; Konar, S. Study of heterogeneous catalysis by iron-squarate based 3d metal organic framework for the transformation of tetrazines to oxadiazole derivatives. Inorg. Chem. 2014, 53, 7071–7073. [Google Scholar] [CrossRef]
  86. Kandambeth, S.; Kale, V.S.; Fan, D.; Bau, J.A.; Bhatt, P.M.; Zhou, S.; Shkurenko, A.; Rueping, M.; Maurin, G.; Shekhah, O.; et al. Unveiling Chemically Robust Bimetallic Squarate-Based Metal–Organic Frameworks for Electrocatalytic Oxygen Evolution Reaction. Adv. Energy Mater. 2023, 13, 2202964. [Google Scholar] [CrossRef]
  87. Zheng, X.; Jia, G.; Fan, G.; Luo, W.; Li, Z.; Zou, Z. Modulation of Disordered Coordination Degree Based on Surface Defective Metal–Organic Framework Derivatives toward Boosting Oxygen Evolution Electrocatalysis. Small 2020, 16, 2003630. [Google Scholar] [CrossRef]
  88. Wang, Z.; Liu, Z.; Xie, C.; Wang, R.; Sun, D. Rare-earth squarate frameworks with scu topology. Dalton Trans. 2022, 51, 18378–18382. [Google Scholar] [CrossRef]
  89. Zhang, W.; Zheng, X.; Jia, G.; Chi, H.; Lin, B.; Qin, H.; Xie, H.; Yuan, Y.; Fu, D. Squarate-Based Metal-Organic Frameworks for Highly Selective and Sensitive Electrochemical Sensing of Dopamine. J. Electrochem. Soc. 2022, 169, 116504. [Google Scholar] [CrossRef]
  90. Priya Vadhana, K.T.; Vairam, S.; Ushadevi, B.; Parveen, S. New Mg(II) and Ca(II) Mixed Strontium Squarates: Structural Characterization, DNA/BSA Interaction, Antioxidant and Anticancer Activities. J. Clust. Sci. 2021, 33, 867–885. [Google Scholar] [CrossRef]
  91. Malerich, P.; Hagihara, K.; Rawal, V.H. Chiral Squaramide Derivatives are Excellent Hydrogen Bond Donor Catalysts. J. Am. Chem. Soc. 2008, 130, 14416. [Google Scholar] [CrossRef] [PubMed]
  92. McGuirk, C.M.; Katz, M.J.; Stern, C.L.; Sarjeant, A.A.; Hupp, J.T.; Farha, O.K.; Mirkin, C.A. Turning On Catalysis: Incorporation of a Hydrogen-Bond-Donating Squaramide into a Zr Metal-Organic Framework. J. Am. Chem. Soc. 2015, 137, 919. [Google Scholar] [CrossRef] [PubMed]
  93. Zhang, X.; Zhang, Z.; Boissonnault, J.; Cohen, S.M. Design and Synthesis of Squaramide-based MOFs as Efficient MOF-supported Hydrogen Organocatalysts. Chem. Comm. 2016, 52, 8585. [Google Scholar] [CrossRef]
  94. Broto-Ribas, A.; Vignatti, C.; Jimenez-Almarza, A.; Luis-Barrera, J.; Dolatkhah, Z.; Gándara, F.; Imaz, I.; Mas-Ballesté, R.; Alemán, J.; Maspoch, D. Heterogeneous Catalysts with Programmable Topologies Generated by Reticulation of Organocatalysts into Metal-Organic Frameworks: The Case of Squaramide. Nano Res. 2021, 14, 458. [Google Scholar] [CrossRef]
  95. Vignatti, C.; Luis-Barrera, J.; Guillerm, V.; Imaz, I.; Mas-Ballesté. Squaramide-IRMOF-16 Analogue for Catalysis of Solvent-Free, Epoxide Ring-Opening Tandem and Multicomponent Reactions. ChemCatChem 2018, 10, 3995. [Google Scholar] [CrossRef]
  96. Jiang, M.; Li, P.; Wu, P.; Zhang, F.; Tian, X.; Deng, C.; Wang, J. A Squaramide-Based Metal Organic Framework as a Luminescent Sensor for Detection of Lactose in Aqueous Solution and in Milk. Chem. Comm. 2018, 54, 9131. [Google Scholar] [CrossRef]
  97. Cohen, S.M.; Zhang, Z.; Boissonnault, J.A. Toward “MetalloMOFzymes”: Metal-Organic Frameworks with Single-Site Metal Catalysts for Small-Molecules Transformations. Inorg. Chem. 2016, 55, 7281. [Google Scholar] [CrossRef]
  98. Kurmoo, M.; Kumagai, H.; Chapman, K.W.; Kepert, C.J. Reversible ferromagnetic–antiferromagnetic transformation upon dehydration–hydration of the nanoporous coordination framework, [Co3(OH)2(C4O4)2]·3H2O. Chem. Commun. 2005, 24, 3012–3014. [Google Scholar] [CrossRef]
  99. Goswami, S.; Adhikary, A.; Jena, H.S.; Biswas, S.; Konar, S. A 3D iron(II)-based MOF with squashed cuboctahedral nanoscopic cages showing spin-canted long-range antiferromagnetic ordering. Inorg. Chem. 2013, 52, 12064–12069. [Google Scholar] [CrossRef]
  100. Seco, J.M.; Calahorro, A.J.; Sebastian, E.S.; Salinas-Castillo, A.; Colacio, E.; Rodríguez-Diéguez, A. Experimental and theoretical study of photoluminescence and magnetic properties of metal–organic polymers based on squarate and tetrazolate moieties containing linkers. New J. Chem. 2015, 39, 9926–9930. [Google Scholar] [CrossRef]
  101. Wang, C.C.; Chung, W.C.; Lin, H.W.; Dai, S.C.; Shiu, J.S.; Lee, G.H.; Sheu, H.S.; Lee, W. Assembly of two Zinc(II)-squarate coordination polymers with noncovalent and covalent bonds derived from flexible ligands, 1,2-bis(4-pyridyl)ethane (dpe). CrystEngComm 2011, 13, 2130–2136. [Google Scholar] [CrossRef]
  102. Brenner, N.; Sperling, J.M.; Poe, T.N.; Celis-Barros, C.; Brittain, K.; Villa, E.M.; Albrecht-Schmitt, T.E.; Polinski, M.J. Trivalent f-Element Squarates, Squarate-Oxalates, and Cationic Materials, and the Determination of the Nine-Coordinate Ionic Radius of Cf(III). Inorg. Chem. 2020, 59, 9384–9395. [Google Scholar] [CrossRef] [PubMed]
  103. Huang, Y.T.; Lai, Y.C.; Wang, S.L. Intrinsic Green Phosphor Containing a {Y5O22} Pentamer Unit and a Carbonate Ligand Generated In Situ from Squaric Acid. Chem. Eur. J. 2012, 18, 8614–8616. [Google Scholar] [CrossRef]
  104. Liu, Z.; Li, Q.; Wang, Y.; Ma, R.; Sun, J.; Deng, J.; Chen, J.; Sun, D.; Xing, X. Facile Synthesis of Dicelike Cobalt Squarate Cages through a Spontaneous Dissolution-Regrowth Process. Chem. Mater. 2020, 32, 6765–6771. [Google Scholar] [CrossRef]
  105. Ke, X.J.; Li, D.S.; Zhao, J.; Bai, L.; Yang, J.J.; Duan, Y.P. Unique entangling CdII-framework featuring 2D → 3D inclined polycatenate motif and (4,6)-connected self-catenated H-bonding topology. Inorg. Chem. Commun. 2012, 21, 129–132. [Google Scholar] [CrossRef]
  106. Bensaddek, A.; Akkari, H.; Kinzhybalo, V. A Novel Layered Neodymium Squarate MOF Intercalating Free Ammonium and Squarate Ions {(NH4)2[Nd2(H2O)10(C4O4)3]C4O4}n: Synthesis, Crystal Structure and Thermal Decomposition. J. Inorg. Organomet. Polym. 2019, 29, 302–307. [Google Scholar] [CrossRef]
  107. Wang, C.-C.; Wang, Y.-F.; Ke, S.-Y.; Xiu, Y.; Lee, G.-H.; Chen, B.-H.; Chuang, Y.-C.; Wang, C.-C.; Wang, Y.-F.; Ke, S.-Y.; et al. Synthesis, structural characterization and thermal stability of a 2D layered Cd(II) coordination polymer constructed from squarate (C4O42−) and 2,2’-bis(2-pyridyl)ethylene (2,2’-bpe) ligands. AIMS Mater. Sci. 2018, 5, 145–155. [Google Scholar] [CrossRef]
  108. Liu, C.M.; Zhang, D.; Hao, X.; Zhu, D.-B. Field-Induced Relaxation of Magnetization in a Three-Dimensional LnMOF with the Second Bridging Ligand Squarate. ACS Omega 2016, 1, 286–292. [Google Scholar] [CrossRef]
  109. Ghosh, A.K.; Ghoshal, D.; Zangrando, E.; Ribas, J.; Ray Chaudhuri, N. Structural diversity in manganese squarate frameworks using N,N-donor chelating/bridging ligands: Syntheses, crystal structures and magnetic properties. Dalton Trans. 2006, 1554–1563. [Google Scholar] [CrossRef]
  110. Maji, T.K.; Mostafa, G.; Sain, S.; Prasad, J.S.; Chaudhuri, N.R. Construction of a 3D array of cadmium (II) using squarate as a building block. CrystEngComm 2001, 3, 155–158. [Google Scholar] [CrossRef]
  111. Neeraj, S.; Noy, M.L.; Rao, C.N.R.; Cheetham, A.K. Sodalite networks formed by metal squarates. Solid State Sci. 2002, 4, 1231–1236. [Google Scholar]
  112. Wang, C.C.; Yang, C.H.; Lee, G.H.; Tsai, H.L. Syntheses, Structures, and Magnetic Properties of Two 1D, Mixed-Ligand, Metal Coordination Polymers, [M(C4O4)(dpa)(OH2)] (M = CoII, NiII, and ZnII; dpa = 2,2’-dipyridylamine) and [Cu(C4O4)(dpa)(H2O)]2·(H2O). Eur. J. Inorg. Chem. 2005, 2005, 1334–1342. [Google Scholar]
  113. Wang, C.C.; Yang, C.H.; Lee, G.H. Hydrothermal Synthesis and Structural Characterization of Two pH-Controlled Cd–Squarate Coordination Frameworks, [Cd2(C4O4)2.5(H2O)4]·(dpaH)·1.5(H2O) and [Cd(C4O4)(dpa)(OH2)] (dpa = 2,2′-dipyridylamine). Eur. J. Inorg. Chem. 2006, 2006, 820–826. [Google Scholar]
  114. Meng, L.; Liang, Y.Y.; Mei, L.; Geng, J.S.; Hu, K.Q.; Yu, J.P.; Wang, X.P.; Fujita, T.; Chai, Z.F.; Shi, W.Q. Mixed-Ligand Uranyl Squarate Coordination Polymers: Structure Regulation and Redox Activity. Inorg. Chem. 2022, 61, 302–316. [Google Scholar]
  115. Wang, C.-C.; Ke, S.-Y.; Feng, Y.; Ho, M.-L.; Chang, C.-K.; Chuang, Y.-C.; Lee, G.-H. Synthesis, Structural Characterization and Ligand-Enhanced Photo-Induced Color-Changing Behavior of Two Hydrogen-Bonded Ho(III)-Squarate Supramolecular Compounds. Polymers 2019, 11, 1369. [Google Scholar] [CrossRef]
  116. Zhan, D.; Xu, N.; Du, S.; Ju, Z.; Yuan, D. Structures and Catalytic Properties of two New Squaramide-decorated Cd-MOFs. Z. Anorg. Allg. Chem. 2022, 648, e202200064. [Google Scholar]
  117. Lenz, A.; Ojamäe, L. A theoretical study of water clusters: The relation between hydrogen-bond topology and interaction energy from quantum-chemical computations for clusters with up to 22 molecules. Phys. Chem. Chem. Phys. 2005, 7, 1905. [Google Scholar]
  118. Matar, S.; Hatch, L.F. Chemistry of Petrochemical Processes, 2nd ed.; Elsevier Science & Technology: Centro Rio de Janeiro, Brazil, 2001. [Google Scholar]
  119. Friedrich, M.F.; Lucas, M.; Claus, P. Selective Hydrogenation of Propyne on a Solid Pd/Al2O3 Catalyst Modified with Ionic Liquid Layer (SCILL). Catal. Commun. 2017, 88, 73–76. [Google Scholar] [CrossRef]
  120. Prohens, R.; Portell, A.; Font-Bardia, M.; Bauzá, A.; Frontera, A. A combined crystallographic and theoretical study of weak intermolecular interactions in crystalline squaric acid esters and amides. CrystEngComm 2017, 19, 3071. [Google Scholar]
  121. Ran, J.; Wong, M.W. Saturated Hydrocarbon−Benzene Complexes:  Theoretical Study of Cooperative CH/π Interactions. J. Phys. Chem. A 2006, 110, 9702. [Google Scholar]
  122. Chen, Y.; Lu, W.; Schröder, M.; Yang, S. Analysis and Refinement of Host–Guest Interactions in Metal–Organic Frameworks. Acc. Chem. Res. 2023, 56, 2569. [Google Scholar] [CrossRef]
Crystals 15 00294 g002
Figure 2. (Top): acidity of squaric acid. (Bottom): resonance stabilization of the squarate dianion.
Figure 2. (Top): acidity of squaric acid. (Bottom): resonance stabilization of the squarate dianion.
Crystals 15 00294 g002
Crystals 15 00294 g003
Figure 3. (Top): Commonly known squarate derivatives. (Bottom): Preparation of the mono- and di-squaramides.
Figure 3. (Top): Commonly known squarate derivatives. (Bottom): Preparation of the mono- and di-squaramides.
Crystals 15 00294 g003
Crystals 15 00294 g004
Figure 4. Squaramide donor and acceptor hydrogen bond pattern and its main resonance form.
Figure 4. Squaramide donor and acceptor hydrogen bond pattern and its main resonance form.
Crystals 15 00294 g004
Crystals 15 00294 g005
Figure 5. Microwave-assisted synthesis of squaric acid monoamides in water.
Figure 5. Microwave-assisted synthesis of squaric acid monoamides in water.
Crystals 15 00294 g005
Crystals 15 00294 g006
Figure 6. Coordination modes of squarate in the construction of extended 1D, 2D, and 3D networks. (a) µ1,2,3,4-tetrakis-monodentate, (b) µ1,2,3-tris-monodentate, (c) µ1,2-bis-monodentate, (d) µ1,3-bis-monodentate, (e) bidentate µ2-, (f) bidentate/monodentate µ3-, (g) bidentate/monodentate µ4-, (h) bidentate/monodentate µ6-, (i) monodentate µ4-, (j) monodentate µ6-, (k) bidentate/monodentate µ5-. M = Metal center atom.
Figure 6. Coordination modes of squarate in the construction of extended 1D, 2D, and 3D networks. (a) µ1,2,3,4-tetrakis-monodentate, (b) µ1,2,3-tris-monodentate, (c) µ1,2-bis-monodentate, (d) µ1,3-bis-monodentate, (e) bidentate µ2-, (f) bidentate/monodentate µ3-, (g) bidentate/monodentate µ4-, (h) bidentate/monodentate µ6-, (i) monodentate µ4-, (j) monodentate µ6-, (k) bidentate/monodentate µ5-. M = Metal center atom.
Crystals 15 00294 g006
Crystals 15 00294 g007
Figure 7. Partial top and side views of the Ti(IV) squarate MOF solid state architecture and computational model of the MOF–water supramolecular complex. The CSD code is also indicated. The type of NCI involved is indicated in red. Distance in Å. O atoms are colored in red, C atoms in grey, Ti atoms in silver and H atoms in white.
Figure 7. Partial top and side views of the Ti(IV) squarate MOF solid state architecture and computational model of the MOF–water supramolecular complex. The CSD code is also indicated. The type of NCI involved is indicated in red. Distance in Å. O atoms are colored in red, C atoms in grey, Ti atoms in silver and H atoms in white.
Crystals 15 00294 g007
Crystals 15 00294 g008
Figure 8. Partial top and side views of the Ca squarate MOF with propadiene (top) and propyne (bottom) adsorbed including their respective computational models. The CSD codes are also indicated. The type of NCI involved is indicated in red. Distances in Å. O atoms are colored in red, C atoms in grey, Ca atoms in yellow and H atoms in white.
Figure 8. Partial top and side views of the Ca squarate MOF with propadiene (top) and propyne (bottom) adsorbed including their respective computational models. The CSD codes are also indicated. The type of NCI involved is indicated in red. Distances in Å. O atoms are colored in red, C atoms in grey, Ca atoms in yellow and H atoms in white.
Crystals 15 00294 g008
Crystals 15 00294 g009
Figure 9. Partial top and side views of the Zr squarate MOF solid state architecture with O3 adsorbed and the computational model used. The type of NCI involved is indicated in red. The CSD code is also indicated. Distances in Å. O atoms are colored in red, C atoms in grey, Zr atoms in light blue and H atoms in white.
Figure 9. Partial top and side views of the Zr squarate MOF solid state architecture with O3 adsorbed and the computational model used. The type of NCI involved is indicated in red. The CSD code is also indicated. Distances in Å. O atoms are colored in red, C atoms in grey, Zr atoms in light blue and H atoms in white.
Crystals 15 00294 g009
Crystals 15 00294 g010
Figure 10. Partial top and side views of the Ni squarate MOF solid state architecture with O2 adsorbed and the computational model used. The type of NCI involved is indicated in red. The CSD code is also indicated. Distances in Å. O atoms are colored in red, C atoms in grey, Fe and Ni atoms in dark blue and H atoms in white.
Figure 10. Partial top and side views of the Ni squarate MOF solid state architecture with O2 adsorbed and the computational model used. The type of NCI involved is indicated in red. The CSD code is also indicated. Distances in Å. O atoms are colored in red, C atoms in grey, Fe and Ni atoms in dark blue and H atoms in white.
Crystals 15 00294 g010
Table 2. Molecular formulae (including the CSD ID), the noncovalent forces involved (NCIs), total energies of MOF (EMOF) and its corresponding fragments (EFrag) in Hartrees, electronic multiplicity of the metal center, and counterpoise corrected interaction (ΔEBSSE, in kcal/mol) energy for each of the five selected structures.
Table 2. Molecular formulae (including the CSD ID), the noncovalent forces involved (NCIs), total energies of MOF (EMOF) and its corresponding fragments (EFrag) in Hartrees, electronic multiplicity of the metal center, and counterpoise corrected interaction (ΔEBSSE, in kcal/mol) energy for each of the five selected structures.
MOF FormulaNCIsEMOFEFragMultiplicity aΔEBSSE
[Ti2O3(SQU)]
CSD ID: 2104929		O···H hydrogen bond−11,974.556−11,898.280/
–76.276		1−0.9
[Ca(SQU)(H2O)]
CSD ID: 20190731		CH–π and π–π stacking interactions−9329.507−9213.071/
–116.415		1−12.9
[Ca(SQU)(H2O)]
CSD ID: 20190820		CH–π and π–π stacking interactions−9177.019−9060.578/
−116.422		1−11.9
ZrSQU
CSD ID: 1003940		O···C lone pair–π interactions−8427.827−7544.976/
−882.642		1−32.9
Ni2Fe1 SQU-zbr
CSD ID: 2240469		O···C lone pair–π interactions−25,924.487−25,325.035/
−598.955		Ni(3)/Fe(1)−77.8
a To favor convergence, in the case of the Ni2Fe1 SQU-zbr the global multiplicity of the system used was singlet since there were a pair number of triplet Ni2+ ions.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Nicolau, C.; Piña, M.d.l.N.; Morey, J.; Bauzá, A. On the Importance of Squaramide and Squarate Derivatives as Metal–Organic Framework Building Blocks. Crystals 2025, 15, 294. https://doi.org/10.3390/cryst15040294

AMA Style

Nicolau C, Piña MdlN, Morey J, Bauzá A. On the Importance of Squaramide and Squarate Derivatives as Metal–Organic Framework Building Blocks. Crystals. 2025; 15(4):294. https://doi.org/10.3390/cryst15040294

Chicago/Turabian Style

Nicolau, Catalina, María de las Nieves Piña, Jeroni Morey, and Antonio Bauzá. 2025. "On the Importance of Squaramide and Squarate Derivatives as Metal–Organic Framework Building Blocks" Crystals 15, no. 4: 294. https://doi.org/10.3390/cryst15040294

APA Style

Nicolau, C., Piña, M. d. l. N., Morey, J., & Bauzá, A. (2025). On the Importance of Squaramide and Squarate Derivatives as Metal–Organic Framework Building Blocks. Crystals, 15(4), 294. https://doi.org/10.3390/cryst15040294

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop