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A special issue of Chemistry (ISSN 2624-8549). This special issue belongs to the section "Supramolecular Chemistry".

Deadline for manuscript submissions: closed (31 May 2020) | Viewed by 51732

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Special Issue Editor

Prof. Dr. Catherine Housecroft

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Department of Chemistry, University of Basel, Building 1095, Mattenstrasse 22, Postfach, CH-4002 Basel, Switzerland
Interests: light harvesting using inorganic coordination complexes as dyes in dye-sensitized solar cells (DSCs); development of emissive complexes for application in light-emitting electrochemical cells (LECs); water splitting and water oxidation catalysts; functional coordination polymers and networks; chemical education
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Dear Colleagues,

This Special Issue is one of the first for the new MDPI flagship journal Chemistry (ISSN 2624-8549) which has a broad remit for publishing original research in all areas of chemistry. The theme of this issue is Supramolecular Chemistry in the 3rd Millennium and I am sure that this topic will attract many exciting contributions. We chose this topic because it encompasses the unity of contemporary pluridisciplinary science, in which organic, inorganic, physical and theoretical chemists work together with molecular biologists and physicists to develop a systems-level understanding of molecular interactions. The description of supramolecular chemistry as ‘chemistry beyond the molecule’ (Jean-Marie Lehn, Nobel Lecture and Gautam R. Desiraju, Nature, 2001, 412, 397) addresses the wide variety of weak, non-covalent interactions that are the basis for the assembly of supramolecular architectures, molecular receptors and molecular recognition, programed molecular systems, dynamic combinatorial libraries, coordination networks and functional supramolecular materials. We welcome submissions from all disciplines involved in this exciting and evolving area of science.

Prof. Dr. Catherine Housecroft
Guest Editor

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Published Papers (19 papers)

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Editorial

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Open AccessEditorial

Supramolecular Chemistry in the 3rd Millennium

Catherine E. Housecroft

Chemistry 2021, 3(2), 509-510; https://doi.org/10.3390/chemistry3020035 - 08 Apr 2021

Cited by 3 | Viewed by 1656

Abstract

The description of supramolecular chemistry as “chemistry beyond the molecule” (Jean-Marie Lehn, 1987 Nobel Lecture and Gautam R [...] Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

Research

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Open AccessArticle

Exploring the Structural Chemistry of Pyrophosphoramides: N,N′,N″,N‴-Tetraisopropylpyrophosphoramide

Duncan Micallef

Liana Vella-Zarb

and

Ulrich Baisch

Chemistry 2021, 3(1), 149-163; https://doi.org/10.3390/chemistry3010013 - 28 Jan 2021

Cited by 1 | Viewed by 1620

Abstract

N,N′,N″,N‴-Tetraisopropylpyrophosphoramide 1 is a pyrophosphoramide with documented butyrylcholinesterase inhibition, a property shared with the more widely studied octamethylphosphoramide (Schradan). Unlike Schradan, 1 is a solid at room temperature making it one of a few known pyrophosphoramide solids. The crystal structure of 1 was determined by single-crystal X-ray diffraction and compared with that of other previously described solid pyrophosphoramides. The pyrophosphoramide discussed in this study was synthesised by reacting iso-propyl amine with pyrophosphoryl tetrachloride under anhydrous conditions. A unique supramolecular motif was observed when compared with previously published pyrophosphoramide structures having two different intermolecular hydrogen bonding synthons. Furthermore, the potential of a wider variety of supramolecular structures in which similar pyrophosphoramides can crystallise was recognised. Proton (¹H) and Phosphorus 31 (³¹P) Nuclear Magnetic Resonance (NMR) spectroscopy, infrared (IR) spectroscopy, mass spectrometry (MS) were carried out to complete the analysis of the compound. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Understanding Conformational Polymorphism in Ganciclovir: A Holistic Approach

Lorella Spiteri

Ulrich Baisch

and

Liana Vella-Zarb

Chemistry 2021, 3(1), 126-137; https://doi.org/10.3390/chemistry3010010 - 26 Jan 2021

Cited by 1 | Viewed by 1866

Abstract

We present a holistic crystallographic study of the antiviral ganciclovir, including insights into its solid-state behavior, which could prove useful during drug development, making the process more sustainable. A newly developed methodology was used incorporating a combination of statistical and thermodynamic approaches, which can be applied to various crystalline materials. We demonstrate how the chemical environment and orientation of a functional group can affect its accessibility for participation in hydrogen bonding. The difference in the nature and strength of intermolecular contacts between the two anhydrous forms, exposed through full interaction maps and Hirshfeld surfaces, leads to the manifestation of conformational polymorphism. Variations in the intramolecular geometry and intermolecular interactions of both forms of ganciclovir were identified as possible predictors for their relative thermodynamic stability. It was shown through energy frameworks how the extensive supramolecular network of contacts in form I causes a higher level of compactness and lower enthalpy relative to form II. The likelihood of the material to exhibit polymorphism was assessed through a hydrogen bond propensity model, which predicted a high probability associated with the formation of other relatively stable forms. However, this model failed to classify the stability of form I appropriately, suggesting that it might not have fully captured the collective impacts which govern polymorphic stability. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Hydrogen and Halogen Bond Mediated Coordination Polymers of Chloro-Substituted Pyrazin-2-Amine Copper(I) Bromide Complexes

and

Chemistry 2020, 2(3), 700-713; https://doi.org/10.3390/chemistry2030045 - 05 Aug 2020

Cited by 2 | Viewed by 3284

Abstract

A new class of six mono- (1; 3-Cl-, 2; 5-Cl-, 3; 6-Cl-) and di-(4; 3,6-Cl, 5; 5,6-Cl-, 6; 3,5-Cl-) chloro-substituted pyrazin-2-amine ligands (1–6) form complexes with copper (I) bromide, to give 1D and 2D coordination polymers through a combination of halogen and hydrogen bonding that were characterized by X-ray diffraction analysis. These Cu(I) complexes were prepared indirectly from the ligands and CuBr₂ via an in situ redox process in moderate to high yields. Four of the pyrazine ligands, 1, 4–6 were found to favor a monodentate mode of coordination to one Cu^I ion. The absence of a C6-chloro substituent in ligands 1, 2 and 6 supported N1–Cu coordination over the alternative N4–Cu coordination mode evidenced for ligands 4 and 5. These monodentate systems afforded predominantly hydrogen bond (HB) networks containing a catenated (μ₃-bromo)-Cu^I ‘staircase’ motif, with a network of ‘cooperative’ halogen bonds (XB), leading to infinite polymeric structures. Alternatively, ligands 2 and 3 preferred a μ₂-N,N’ bridging mode leading to three different polymeric structures. These adopt the (μ₃-bromo)-Cu^I ‘staircase’ motif observed in the monodentate ligands, a unique single (μ₂-bromo)-Cu^I chain, or a discrete Cu₂Br₂ rhomboid (μ₂-bromo)-Cu^I dimer. Two main HB patterns afforded by self-complimentary dimerization of the amino pyrazines described by the graph set notation R₂²(8) and non-cyclic intermolecular N–H∙∙∙N’ or N–H∙∙∙Br–Cu leading to infinite polymeric structures are discussed. The cooperative halogen bonding between C–Cl∙∙∙Cl–C and the C–Cl∙∙∙Br–Cu XB contacts are less than the sum of the van der Waals radii of participating atoms, with the latter ranging from 3.4178(14) to 3.582(15) Å. In all cases, the mode of coordination and pyrazine ring substituents affect the pattern of HBs and XBs in these supramolecular structures. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Supramolecular Assemblies of Trinuclear Copper(II)-Pyrazolato Units: A Structural, Magnetic and EPR Study

Kaige Shi

Logesh Mathivathanan

Radovan Herchel

Athanassios K. Boudalis

and

Raphael G. Raptis

Chemistry 2020, 2(3), 626-644; https://doi.org/10.3390/chemistry2030039 - 01 Jul 2020

Cited by 3 | Viewed by 2903

Abstract

Two anionic complexes, {[Cu₃(µ₃-OH)(µ-4-Ph-pz)₃Cl₃]₂[Cu(4-Ph-pzH)₄](µ-Cl)₂}²⁻ (1) and [Cu₃(µ₃-OH)(µ-pz)₃(µ_1,1-N₃)₂(N₃)]⁻ (2), crystallize [...] Read more.

Two anionic complexes, {[Cu₃(µ₃-OH)(µ-4-Ph-pz)₃Cl₃]₂[Cu(4-Ph-pzH)₄](µ-Cl)₂}²⁻ (1) and [Cu₃(µ₃-OH)(µ-pz)₃(µ_1,1-N₃)₂(N₃)]⁻ (2), crystallize as one-dimensional polymers, held together by weak Cu-(µ-Cl) and Cu-(µ-N₃) interactions, respectively. Variable temperature magnetic susceptibility analyses determined the dominant antiferromagnetic intra-Cu₃ exchange parameters in the solid state for both complexes, whereas the weak ferromagnetic inter-Cu₃ interactions manifested also in the solid state EPR spectra, are absent in the corresponding frozen solution spectra. DFT calculations were employed to support the results of the magnetic susceptibility analyses. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Towards a Generalized Synthetic Strategy for Variable Sized Enantiopure M₄L₄ Helicates

and

Chemistry 2020, 2(3), 613-625; https://doi.org/10.3390/chemistry2030038 - 28 Jun 2020

Cited by 6 | Viewed by 2612

Abstract

The reliable and predictable synthesis of enantiopure coordination cages is an important step towards the realization of discrete cages capable of enantioselective discrimination. We have built upon our initial report of a lantern-type helical cage in attempts to expand the synthesis into a general approach. The use of a longer, flexible diacid ligand results in the anticipated cage [Cu₄(L1)₄(solvent)₄] with a similar helical pitch to that previously observed and a cavity approximately 30% larger. Using a shorter, more rigid ligand gave rise to a strained, conjoined cage-type complex when using DABCO as an internal bridging ligand, [{Co₄(L2)₄(DABCO)(OH₂)_x}₂ (DABCO)]. The expected paddlewheel motif only forms for one of the Co₂ units within each cage, with the other end adopting a “partial paddlewheel” with aqua ligands completing the coordination sphere of the externally facing metal ion. The generic approach of using chiral diacids to construct lantern-type cages is partially borne out, with it being apparent that flexibility in the core group is an essential structural feature. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Complementarity in Cyclotricatechylene Assemblies: Symmetric Cages Linked within 3D Cubic Hydrogen Bonded Networks

and

Chemistry 2020, 2(2), 577-590; https://doi.org/10.3390/chemistry2020035 - 11 Jun 2020

Cited by 1 | Viewed by 2164

Abstract

A serendipitous discovery has led to the generation of a family of four compounds in which six components combine to form symmetric metal-cyclotricatechylene (H₆ctc) cages. The four compounds, which have the compositions, [Cs((CH₃)₂CO)₆][K₄(H₆ctc)₄(H₂O)₈][Cs₄(H₂O)₆](PO₄)₃, [Rb((CH₃)₂CO)₆][Rb₂K₂(H₆ctc)₄(H₂O)₆][Rb₄(H₂O)₆](PO₄)₃, [Cs((CH₃)₂CO)₆][K₄(H₆ctc)₄(H₂O)₈]-[Cs(H₂O)₉](SO₄)₃ and [Rb((CH₃)₂CO)₆][Rb₂K₂(H₆ctc)₄(H₂O)₆][Rb(H₂O)₉](SO₄)₃ possess cubic symmetry that arises from the complementary interactions that govern the assembly of the components. The cage cavities contain water molecules and either one or four large alkali metal ions (either Rb⁺ or Cs⁺) which interact with the internal aromatic surfaces of the cage. Each cage is linked to six tetrahedral anions (PO₄³⁻ or SO₄²⁻) through 24 equivalent hydrogen bonds and each anion bridges a pair of cages through eight such hydrogen bonds. An unusual octahedral complex M((CH₃)₂CO)₆⁺ (M = Rb or Cs), in which the M-C=O link is linear, appears to be a key structural component. A feature of this family of crystalline compounds is the presence of a range of complementary interactions which combine to generate materials that exhibit high crystallographic symmetry. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Solvent Effect on the Regulation of Urea Hydrolysis Reactions by Copper Complexes

Caio B. Castro

Rafael G. Silveira

Felippe M. Colombari

André Farias de Moura

Otaciro R. Nascimento

and

Caterina G. C. Marques Netto

Chemistry 2020, 2(2), 525-544; https://doi.org/10.3390/chemistry2020032 - 02 Jun 2020

Cited by 3 | Viewed by 3724

Abstract

Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (Cu^IIL2) and ethoxyl (Cu^IIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (Cu^IIL1), methyl (Cu^IIL3), or t-butyl (Cu^IIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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A Study of the Interaction between Cucurbit[7]uril and Alkyl Substituted 4-Pyrrolidinopyridinium Salts

and

Chemistry 2020, 2(2), 262-273; https://doi.org/10.3390/chemistry2020017 - 14 Apr 2020

Cited by 4 | Viewed by 1871

Abstract

The interaction between cucurbit[7]uril (Q[7]) and a series of 4-pyrrolidinopyridinium salts bearing aliphatic substituents at the pyridinium nitrogen, namely 4-(C₄H₈N)C₅H₅NRBr, where R = H (C0), Et (C2), n-butyl (C4), n-hexyl (C6), has been [...] Read more.

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessFeature PaperCommunication

A Brucite-Like Mixed-Valent Cluster Capped by [Mn^IIIp-^tBu-calix[4]arene]⁻ Moieties

and

Chemistry 2020, 2(2), 253-261; https://doi.org/10.3390/chemistry2020016 - 09 Apr 2020

Cited by 2 | Viewed by 2655

Abstract

p-^tBu-calix[4]arene (H₄TBC[4]) has proven to be an incredibly versatile ligand for the synthesis of 3d- and 3d/4f- clusters, in particular those containing mixed-valent Mn ions. These are of interest to the magnetochemist for the diversity of magnetic behaviours that can be shown, along with a huge variety of nuclearities and topologies accessible, which allow one to outline magneto-structural correlations and a quantitative understanding of their properties. This contribution reports the synthesis, analysis and magnetic properties of a Brucite-like Mn-oxo/hydroxo octanuclear fragment encapsulated within/capped by four [Mn^III-TBC[4]]⁻ moieties. A diol coligand in the reaction mixture plays a seemingly important role in determining the outcome, though it is not incorporated in the final structure. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

From Frustrated Packing to Tecton-Driven Porous Molecular Solids

Chamara A. Gunawardana

Abhijeet S. Sinha

Eric W. Reinheimer

and

Christer B. Aakeröy

Chemistry 2020, 2(1), 179-192; https://doi.org/10.3390/chemistry2010011 - 13 Mar 2020

Cited by 6 | Viewed by 3556

Abstract

Structurally divergent molecules containing bulky substituents tend to produce porous materials via frustrated packing. Two rigid tetrahedral cores, tetraphenylmethane and 1,3,5,7-tetraphenyladamantane, grafted peripherally with four (trimethylsilyl)ethynyl moieties, were found to have only isolated voids in their crystal structures. Hence, they were modified into tecton-like entities, tetrakis(4-(iodoethynyl)phenyl)methane [I₄TEPM] and 1,3,5,7-tetrakis(4-(iodoethynyl)phenyl)adamantane [I₄TEPA], in order to deliberately use the motif-forming characteristics of iodoethynyl units to enhance crystal porosity. I₄TEPM not only holds increased free volume compared to its precursor, but also forms one-dimensional channels. Furthermore, it readily co-crystallizes with Lewis basic solvents to afford two-component porous crystals. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessArticle

Controlled Stepwise Synthesis and Characterization of a Ternary Multicomponent Crystal with 2-Methylresorcinol

Daniel Komisarek

Carsten Schauerte

and

Klaus Merz

Chemistry 2020, 2(1), 93-100; https://doi.org/10.3390/chemistry2010009 - 04 Mar 2020

Cited by 3 | Viewed by 2155

Abstract

A typical approach of a multicomponent crystal design starts with a retrosynthetic analysis of the target molecule followed by a one-pot reaction of all components. To develop protocols for multicomponent crystal syntheses, controlled stepwise syntheses of a selected crystalline ternary multicomponent system 1 involving 2-methylresorcinol (MRS), tetramethyl-pyrazine (TMP), and 1,2-bis(4-pyridyl)ethane (BPE) are presented. The obtained binary cocrystals 2 (involving MRS and TMP) and 3 (involving MRS and BPE) as well as the final resulting ternary multicomponent system 1 were characterized by X-ray analysis. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessFeature PaperArticle

Metallosupramolecular Compounds Based on Copper(II/I) Chloride and Two Bis-Tetrazole Organosulfur Ligands

Olaya Gómez-Paz

Rosa Carballo

Ana Belén Lago

and

Ezequiel M. Vázquez-López

Chemistry 2020, 2(1), 33-49; https://doi.org/10.3390/chemistry2010005 - 04 Feb 2020

Cited by 3 | Viewed by 2349

Abstract

The present work assesses the ability of two flexible bis-tetrazole organosulfur ligands to build up different metallosupramolecular compounds based on the analysis of the different supramolecular interactions. The reaction of copper(II) chloride dihydrate with the N,N’-donor dithioether ligands bis(1-methyl-1H-tetrazole-5-ylthio)methane (BMTTM) and 1,2-bis(1-methyl-1H-tetrazole-5-ylthio)ethane (BMTTE) was investigated using different synthetic methods. Four compounds have been obtained as single crystals: two pseudopolymorphic 1D Cu(II) coordination polymers with the ligand BMTTM, a 2D Cu(II) coordination polymer and a discrete Cu(I) tetramer with the BMTTE ligand. The effects of the weak interactions on the crystal packing and the Hirshfeld surfaces of the structures were analyzed to clarify the nature of the intermolecular interactions. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessFeature PaperArticle

Catalysis of an Aldol Condensation Using a Coordination Cage

Cristina Mozaceanu

Christopher G. P. Taylor

Jerico R. Piper

Stephen P. Argent

and

Michael D. Ward

Chemistry 2020, 2(1), 22-32; https://doi.org/10.3390/chemistry2010004 - 25 Jan 2020

Cited by 11 | Viewed by 3461

Abstract

The aldol condensation of indane-1,3-dione (ID) to give ‘bindone’ in water is catalysed by an M₈L₁₂ cubic coordination cage (H^w). The absolute rate of reaction is slow under weakly acidic conditions (pH 3–4), but in the absence of a catalyst it is undetectable. In water, the binding constant of ID in the cavity of H^w is ca. 2.4 (±1.2) × 10³ M⁻¹, giving a ∆G for the binding of −19.3 (±1.2) kJ mol⁻¹. The crystal structure of the complex revealed the presence of two molecules of the guest ID stacked inside the cavity, giving a packing coefficient of 74% as well as another molecule hydrogen-bonded to the cage’s exterior surface. We suggest that the catalysis occurs due to the stabilisation of the enolate anion of ID by the 16+ surface of the cage, which also attracts molecules of neutral ID to the surface because of its hydrophobicity. The cage, therefore, brings together neutral ID and its enolate anion via two different interactions to catalyse the reaction, which—as the control experiments show—occurs at the exterior surface of the cage and not inside the cage cavity. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Selective Proton-Mediated Transport by Electrogenic K⁺-Binding Macrocycles

and

Chemistry 2020, 2(1), 11-21; https://doi.org/10.3390/chemistry2010003 - 20 Jan 2020

Cited by 3 | Viewed by 1944

Abstract

Synthetic K⁺-binding macrocycles have potential as therapeutic agents for diseases associated with KcsA K⁺ channel dysfunction. We recently discovered that artificial self-assembled n-alkyl-benzoureido-15-crown-5-ether form selective ion-channels for K⁺ cations, which are highly preferred to Na⁺ cations. Here, we describe an impressive selective activation of the K⁺ transport via electrogenic macrocycles, stimulated by the addition of the carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP) proton carrier. The transport performances show that both the position of branching or the size of appended alkyl arms favor high transport activity and selectivity S_K⁺_/Na⁺ up to 48.8, one of the best values reported up to now. Our study demonstrates that high K⁺/Na⁺ selectivity obtained with natural KcsA K⁺ channels is achievable using simpler artificial macrocycles displaying constitutional functions. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessFeature PaperArticle

Solvatochromism and Selective Sorption of Volatile Organic Solvents in Pyridylbenzoate Metal-Organic Frameworks

Christophe A. Ndamyabera

Savannah C. Zacharias

Clive L. Oliver

and

Susan A. Bourne

Chemistry 2019, 1(1), 111-125; https://doi.org/10.3390/chemistry1010009 - 15 Aug 2019

Cited by 4 | Viewed by 3871

Abstract

Using cobalt(II) as a metal centre with different solvent systems afforded the crystallization of isomorphous metal-organic frameworks {[Co(34pba)(44pba)]·DMF}_n (1) and {[Co(34pba)(44pba)]·(C₃H₆O)}_n (2) from mixed 4-(4-pyridyl)benzoate (44pba) and 3-(4-pyridyl)benzoate (34pba) ligands. Zinc(II) under the same reaction conditions that led to the formation of 1 formed an isostructural {[Zn(34pba)(44pba)]·DMF}_n framework (3). Crystal structures of all three MOFs were elucidated and their thermal stabilities were determined. The frameworks of 1, 2, and 3 were activated under vacuum to form the desolvated forms 1d, 2d, and 3d, respectively. PXRD results showed that 1d and 2d were identical, consequently, 1d and 3d were then investigated for sorption of volatile organic compounds (VOCs) containing either chloro or amine moieties. Thermogravimetric analysis (TGA) and nuclear magnetic resonance (NMR) were used to determine the sorption capacity and selectivity for the VOCs. Some sorption products of 1d with amines became amorphous, but the crystalline framework could be recovered on desorption of the amines. Investigation of the sorption of water (H₂O) and ammonia (NH₃) in 1d gave rise to new phases identifiable by means of a colour change (solvatochromism). The kinetics of desorption of DMF, water and ammonia from frameworks 1d and 3d were studied using non-isothermal TGA. Activation energies for both cobalt(II) and zinc(II) frameworks are in the order NH₃ < H₂O < DMF, with values for the 1d analogue always higher than those for 3d. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Open AccessCommunication

Hydroquinone-Based Anion Receptors for Redox-Switchable Chloride Binding

Daniel A. McNaughton

Xiaochen Fu

William Lewis

Deanna M. D’Alessandro

and

Philip A. Gale

Chemistry 2019, 1(1), 80-88; https://doi.org/10.3390/chemistry1010007 - 11 Jul 2019

Cited by 5 | Viewed by 3967

Abstract

A series of chloride receptors has been synthesized containing an amide hydrogen bonding site and a hydroquinone motif. It was anticipated that oxidation of the hydroquinone unit to quinone would greatly the diminish chloride binding affinity of these receptors. A conformational switch is promoted in the quinone form through the formation of an intramolecular hydrogen bond between the amide and the quinone carbonyl, which blocks the amide binding site. The reversibility of this oxidation process highlighted the potential of these systems for use as redox-switchable receptors. ¹H-NMR binding studies confirmed stronger binding capabilities of the hydroquinone form compared to the quinone; however, X-ray crystal structures of the free hydroquinone receptors revealed the presence of an analogous inhibiting intramolecular hydrogen bond in this state of the receptor. Binding studies also revealed interesting and contrasting trends in chloride affinity when comparing the two switch states, which is dictated by a secondary interaction in the binding mode between the amide carbonyl and the hydroquinone/quinone couple. Additionally, the electrochemical properties of the systems have been explored using cyclic voltammetry and it was observed that the reduction potential of the system was directly related to the expected strength of the internal hydrogen bond. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Review

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Open AccessReview

Combining Coordination and Hydrogen Bonds to Develop Discrete Supramolecular Metalla-Assemblies

Bruno Therrien

Chemistry 2020, 2(2), 565-576; https://doi.org/10.3390/chemistry2020034 - 08 Jun 2020

Cited by 11 | Viewed by 2627

Abstract

In Nature, metal ions play critical roles at different levels, and they are often found in proteins. Therefore, metal ions are naturally incorporated in hydrogen-bonded systems. In addition, the combination of metal coordination and hydrogen bonds have been used extensively to develop supramolecular materials. However, despite this win-win combination between coordination and hydrogen bonds in many supramolecular systems, the same combination remains scarce in the field of coordination-driven self-assemblies. Indeed, as illustrated in this mini-review, only a few discrete supramolecular metalla-assemblies combining coordination and hydrogen bonds can be found in the literature, but that figure might change rapidly. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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Uranyl Ion Complexes of Polycarboxylates: Steps towards Isolated Photoactive Cavities

Jack Harrowfield

and

Pierre Thuéry

Chemistry 2020, 2(1), 63-79; https://doi.org/10.3390/chemistry2010007 - 20 Feb 2020

Cited by 7 | Viewed by 2241

Abstract

Consideration of the extensive family of known uranyl ion complexes of polycarboxylate ligands shows that there are quite numerous examples of crystalline solids containing capsular, closed oligomeric species with the potential for use as selective heterogeneous photo-oxidation catalysts. None of them have yet been assessed for this purpose, and some have obvious deficiencies, although related framework species have been shown to have the necessary luminescence, porosity and, to some degree, selectivity. Aspects of ligand design and complex composition necessary for the synthesis of uranyl ion cages with appropriate luminescence and chemical properties for use in selective photo-oxidation catalysis have been analysed in relation to the characteristics of known capsules. Full article

(This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium)

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