Chemistry

Editorial

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14 pages, 6204 KiB

Open AccessEditorial

Justus von Liebig

by Siegfried Schindler

Chemistry 2023, 5(2), 1046-1059; https://doi.org/10.3390/chemistry5020071 - 6 May 2023

Viewed by 2737

Abstract

This is a short overview of the life and achievements of Justus von Liebig. Clearly, this can only be an incomplete and somewhat personal view of the author, who has been a professor of inorganic chemistry at Justus Liebig University since 2002. Having [...] Read more.

This is a short overview of the life and achievements of Justus von Liebig. Clearly, this can only be an incomplete and somewhat personal view of the author, who has been a professor of inorganic chemistry at Justus Liebig University since 2002. Having already been interested in the work of Liebig for many years, and with a strong connection to the Liebig Museum in Giessen, the author hopes to provide some useful information about this great chemist, one of the founders of modern chemistry. The reader should find many interesting, probably new, facts about Liebig’s major impact on chemistry, agriculture, nutrition, and pharmacology. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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Research

Jump to: Editorial

18 pages, 3075 KiB

Open AccessArticle

In Pursuit of Next Generation N-Heterocyclic Carbene-Stabilized Copper and Silver Precursors for Metalorganic Chemical Vapor Deposition and Atomic Layer Deposition Processes

by Ilamparithy Selvakumar, Nils Boysen, Marco Bürger and Anjana Devi

Chemistry 2023, 5(3), 2038-2055; https://doi.org/10.3390/chemistry5030138 - 20 Sep 2023

Viewed by 2117

Abstract

Volatile, reactive, and thermally stable organometallic copper and silver complexes are of significant interest as precursors for the metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) of ultra-thin metallic films. Well-established Cu^I and Ag^I precursors are commonly stabilized by [...] Read more.

Volatile, reactive, and thermally stable organometallic copper and silver complexes are of significant interest as precursors for the metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) of ultra-thin metallic films. Well-established Cu^I and Ag^I precursors are commonly stabilized by halogens, phosphorous, silicon, and oxygen, potentially leading to the incorporation of these elements as impurities in the thin films. These precursors are typically stabilized by a neutral and anionic ligand. Recent advancements were established by the stabilization of these complexes using N-heterocyclic carbenes (NHCs) as neutral ligands. To further enhance the reactivity, in this study the anionic ligand is sequentially changed from β-diketonates to β-ketoiminates and β-diketiminates, yielding two new Cu^I and two new Ag^I NHC-stabilized complexes in the general form of [M(NHC) (R)] (M = Cu, Ag; R = β-ketoiminate, β-diketiminate). The synthesized complexes were comparatively analyzed in solid, dissolved, and gaseous states. Furthermore, the thermal properties were investigated to assess their potential application in MOCVD or ALD. Among the newly synthesized complexes, the β-diketiminate-based [Cu(tBuNHC) (NacNacMe)] was identified to be the most suitable candidate as a precursor for Cu thin film deposition. The resulting halogen-, oxygen-, and silicon-free Cu^I and Ag^I precursors for MOCVD and ALD applications are established for the first time and set a new baseline for coinage metal precursors. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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29 pages, 5231 KiB

Open AccessArticle

Syntheses, Crystal and Electronic Structures of Rhodium and Iridium Pyridine Di-Imine Complexes with O- and S-Donor Ligands: (Hydroxido, Methoxido and Thiolato)

by Michel Stephan, Max Völker, Matthias Schreyer and Peter Burger

Chemistry 2023, 5(3), 1961-1989; https://doi.org/10.3390/chemistry5030133 - 5 Sep 2023

Cited by 2 | Viewed by 2113

Abstract

The syntheses of new neutral square-planar pyridine di-imine rhodium and iridium complexes with O- and S-donor (OH, OR, SH, SMe and SPh) ligands along with analogous cationic compounds are reported. Their crystal and electronic structures are investigated in detail with a focus on [...] Read more.

The syntheses of new neutral square-planar pyridine di-imine rhodium and iridium complexes with O- and S-donor (OH, OR, SH, SMe and SPh) ligands along with analogous cationic compounds are reported. Their crystal and electronic structures are investigated in detail with a focus on the non-innocence/innocence of the PDI ligand. The oxidation states of the metal centers were analyzed by a variety of experimental (XPS and XAS) and theoretical (LOBA, EOS and OSLO) methods. The dπ-pπ interaction between the metal centers and the π-donor ligands was investigated by theoretical methods and revealed the partial multiple-bond character of the M-O,S bonds. Experimental support is provided by a sizable barrier for the rotation about the Ir-S bond in the methyl thiolato complex and confirmed by DFT and LNO-CCSD(T) calculations. This was corroborated by the high Ir-O and Ir-S bond dissociation enthalpies calculated at the PNO-CCSD(T) level. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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12 pages, 1970 KiB

Open AccessArticle

Unraveling the Synthesis of SbCl(C₃N₆H₄): A Metal-Melaminate Obtained through Deprotonation of Melamine with Antimony(III)Chloride

by Elaheh Bayat, Markus Ströbele and Hans-Jürgen Meyer

Chemistry 2023, 5(2), 1465-1476; https://doi.org/10.3390/chemistry5020099 - 20 Jun 2023

Cited by 4 | Viewed by 2198

Abstract

The discovery of melamine by Justus von Liebig was fundamental for the development of several fields of chemistry. The vast majority of compounds with melamine or melamine derivatives appear as adducts. Herein, we focus on the development of novel compounds containing anionic melamine [...] Read more.

The discovery of melamine by Justus von Liebig was fundamental for the development of several fields of chemistry. The vast majority of compounds with melamine or melamine derivatives appear as adducts. Herein, we focus on the development of novel compounds containing anionic melamine species, namely the melaminates. For this purpose, we analyze the reaction of SbCl₃ with melamine by differential scanning calorimetry (DSC). The whole study includes the synthesis and characterization of three antimony compounds that are obtained during the deprotonation process of melamine to melaminate with the reaction sequence from SbCl₄(C₉N₁₈H₁₉) (1) via (SbCl₄(C₆N₁₂H₁₃))₂ (2) to SbCl(C₃N₆H₄) (3). Compounds are characterized by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), and infrared spectroscopy (IR). The results give an insight into the mechanism of deprotonation of melamine, with the replacement of one, two, or eventually three hydrogen atoms from the three amino groups of melamine. The structure of (3) suggests that metal melaminates are likely to form supramolecular structures or metal-organic frameworks (MOFs). Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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12 pages, 2724 KiB

Open AccessCommunication

Suzuki–Miyaura Reaction in the Presence of N-Acetylcysteamine Thioesters Enables Rapid Synthesis of Biomimetic Polyketide Thioester Surrogates for Biosynthetic Studies

by Sebastian Derra, Luca Schlotte and Frank Hahn

Chemistry 2023, 5(2), 1407-1418; https://doi.org/10.3390/chemistry5020096 - 8 Jun 2023

Cited by 2 | Viewed by 2140

Abstract

Biomimetic N-acetylcysteamine thioesters are essential for the study of polyketide synthases, non-ribosomal peptide synthetases and fatty acid synthases. The chemistry for their preparation is, however, limited by their specific functionalization and their susceptibility to undesired side reactions. Here we report a method [...] Read more.

Biomimetic N-acetylcysteamine thioesters are essential for the study of polyketide synthases, non-ribosomal peptide synthetases and fatty acid synthases. The chemistry for their preparation is, however, limited by their specific functionalization and their susceptibility to undesired side reactions. Here we report a method for the rapid preparation of N-acetylcysteamine (SNAC) 7-hydroxy-2-enethioates, which are suitable for the study of various enzymatic domains of megasynthase enzymes. The method is based on a one-pot sequence of hydroboration and the Suzuki–Miyaura reaction. The optimization of the reaction conditions made it possible to suppress potential side reactions and to introduce the highly functionalized SNAC methacrylate unit in a high yield. The versatility of the sequence was demonstrated by the synthesis of the complex polyketide-SNAC thioesters 12 and 33. Brown crotylation followed by the hydroboration to Suzuki–Miyaura reaction sequence enabled the introduction of the target motif in significantly fewer steps and with a higher overall yield and stereoselectivity than previously described approaches. This is the first report of a transition-metal-catalyzed cross-coupling reaction in the presence of an SNAC thioester. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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17 pages, 6769 KiB

Open AccessArticle

Reactivity of Rare-Earth Oxides in Anhydrous Imidazolium Acetate Ionic Liquids

by Sameera Shah, Tobias Pietsch, Maria Annette Herz, Franziska Jach and Michael Ruck

Chemistry 2023, 5(2), 1378-1394; https://doi.org/10.3390/chemistry5020094 - 2 Jun 2023

Cited by 3 | Viewed by 2166

Abstract

Rare-earth metal sesquioxides (RE₂O₃) are stable compounds that require high activation energies in solid-state reactions or strong acids for dissolution in aqueous media. Alternatively, dissolution and downstream chemistry of RE₂O₃ have been achieved with ionic [...] Read more.

Rare-earth metal sesquioxides (RE₂O₃) are stable compounds that require high activation energies in solid-state reactions or strong acids for dissolution in aqueous media. Alternatively, dissolution and downstream chemistry of RE₂O₃ have been achieved with ionic liquids (ILs), but typically with additional water. In contrast, the anhydrous IL 1-butyl-3-methylimidazolium acetate [BMIm][OAc] dissolves RE₂O₃ for RE = La–Ho and forms homoleptic dinuclear metal complexes that crystallize as [BMIm]₂[RE₂(OAc)₈] salts. Chloride ions promote the dissolution without being included in the compounds. Since the lattice energy of RE₂O₃ increases with decreasing size of the RE³⁺ cation, Ho₂O₃ dissolves very slowly, while the sesquioxides with even smaller cations appear to be inert under the applied conditions. The Sm and Eu complex salts show blue and red photoluminescence and Van Vleck paramagnetism. The proton source for the dissolution is the imidazolium cation. Abstraction of the acidic proton at the C²-atom yields an N-heterocyclic carbene (imidazole-2-ylidene). The IL can be regenerated by subsequent reaction with acetic acid. In the overall process, RE₂O₃ is dissolved by anhydrous acetic acid, a reaction that does not proceed directly. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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14 pages, 3182 KiB

Open AccessArticle

On the Redox Equilibrium of TPP/TPPO Containing Cu(I) and Cu(II) Complexes

by Stephanie L. Faber, Nesrin I. Dilmen and Sabine Becker

Chemistry 2023, 5(2), 1288-1301; https://doi.org/10.3390/chemistry5020087 - 17 May 2023

Cited by 1 | Viewed by 2601

Abstract

Copper(II) clusters of the type [Cu^II₄OCl₆L₄] (L = ligand or solvent) are a well-studied example of inverse coordination compounds. In the past, they have been studied because of their structural, magnetic, and spectroscopic features. They have [...] Read more.

Copper(II) clusters of the type [Cu^II₄OCl₆L₄] (L = ligand or solvent) are a well-studied example of inverse coordination compounds. In the past, they have been studied because of their structural, magnetic, and spectroscopic features. They have long been believed to be redox-inactive compounds, but recent findings indicate a complex chemical equilibrium with diverse mononuclear as well as multinuclear copper(I) and copper(II) compounds. Furthermore, depending on the ligand system, such cluster compounds have proven to be versatile catalysts, e.g., in the oxidation of cyclohexane to adipic acid. This report covers a systematic study of the formation of [Cu^II₄OCl₆(TPP)₄] and [Cu^II₄OCl₆(TPPO)₄] (TPP = triphenylphosphine, PPh₃; TPPO = triphenylphosphine oxide, O=PPh₃) as well as the redox equilibrium of these compounds with mononuclear copper(I) and copper(II) complexes such as [Cu^IICl₂(TPPO)₂], [{Cu^IICl₂}₂(TPPO)₂], [{Cu^IICl₂}₃(TPPO)₂], [{Cu^II₄Cl₄}(TPP)₄], and [Cu^ICl(TPP)_n] (n = 1–3). Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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17 pages, 4227 KiB

Open AccessArticle

Improved Synthesis and Coordination Behavior of 1H-1,2,3-Triazole-4,5-dithiolates (tazdt²⁻) with Ni^II, Pd^II, Pt^II and Co^III

by Nils Pardemann, Alexander Villinger and Wolfram W. Seidel

Chemistry 2023, 5(2), 1271-1287; https://doi.org/10.3390/chemistry5020086 - 17 May 2023

Viewed by 1913

Abstract

A new synthetic route to 1H-1,2,3-triazole-4,5-dithiols (tazdtH₂) as ligands for the coordination of Ni^II, Pd^II, Pt^II and Co^III via the dithiolate unit is presented. Different N-protective groups were introduced with the corresponding azide [...] Read more.

A new synthetic route to 1H-1,2,3-triazole-4,5-dithiols (tazdtH₂) as ligands for the coordination of Ni^II, Pd^II, Pt^II and Co^III via the dithiolate unit is presented. Different N-protective groups were introduced with the corresponding azide via a click-like copper-catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC) and fully characterized by NMR spectroscopy. Possible isomers were isolated and an alternative synthetic route was investigated and discussed. After removal of the benzyl protective groups on sulfur by in situ-generated sodium naphthalide, complexes at the [(dppe)M] (M = Ni, Pd, Pt), [(PPh₃)₂Pt] and [(η⁵-C₅H₅)Co] moieties were prepared and structurally characterized by XRD analysis. In this process, the by-products 11 and 12 as monothiolate derivatives were isolated and structurally characterized as well. With regioselective coordination via the dithiolate unit, the electronic influence of different metals or protective groups at N was investigated and compared spectroscopically by means of UV/Vis spectroscopy and cyclic voltammetry. Complex [(η⁵-C₅H₅)Co(5c)] (10), is subject to a dimerization equilibrium, which was investigated by temperature-dependent NMR and UV/Vis spectroscopy (solution and solid-state). The thermodynamic parameters of the monomer/dimer equilibrium were derived. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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13 pages, 2355 KiB

Open AccessArticle

Modification of the Bridging Unit in Luminescent Pt(II) Complexes Bearing C^N*N and C^N*N^C Ligands

by Stefan Buss, María Victoria Cappellari, Alexander Hepp, Jutta Kösters and Cristian A. Strassert

Chemistry 2023, 5(2), 1243-1255; https://doi.org/10.3390/chemistry5020084 - 15 May 2023

Cited by 4 | Viewed by 1939

Abstract

In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on [...] Read more.

In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on their excited state properties. Hence, a detailed analysis of the different synthetic pathways is presented; the photophysical properties were studied by using steady-state and time-resolved photoluminescence spectroscopy. We determined the absorption and emission spectra, the photoluminescence efficiencies, and the excited state lifetimes of the complexes in fluid solutions at room temperature and frozen glassy matrices at 77 K. Finally, a structure–property relationship was established, showing that the decoration of the bridging unit on the tridentate luminophores only marginally affects the excited state properties, whereas the double cyclometallation related to the tetradentate chelator prolongs the excited state lifetime and increases the photoluminescence quantum yield. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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13 pages, 3496 KiB

Open AccessArticle

Selective Fluorimetric Detection of Pyrimidine Nucleotides in Neutral Aqueous Solution with a Styrylpyridine-Based Cyclophane

by Julika Schlosser, Julian F. M. Hebborn, Daria V. Berdnikova and Heiko Ihmels

Chemistry 2023, 5(2), 1220-1232; https://doi.org/10.3390/chemistry5020082 - 11 May 2023

Cited by 1 | Viewed by 2096

Abstract

A styrylpyridine-containing cyclophane with diethylenetriamine linkers is presented as a host system whose association with representative nucleotides was examined with photometric and fluorimetric titrations. The spectrometric titrations revealed the formation of 1:1 complexes with log K_b values in the range of 2.3–3.2 [...] Read more.

A styrylpyridine-containing cyclophane with diethylenetriamine linkers is presented as a host system whose association with representative nucleotides was examined with photometric and fluorimetric titrations. The spectrometric titrations revealed the formation of 1:1 complexes with log K_b values in the range of 2.3–3.2 for pyrimidine nucleotides TMP (thymidine monophosphate), TTP (thymidine triphosphate) and CMP (cytidine monophosphate) and 3.8–5.0 for purine nucleotides AMP (adenosine monophosphate), ATP (adenosine triphosphate), and dGMP (deoxyguanosine monophosphate). Notably, in a neutral buffer solution, the fluorimetric response to the complex formation depends on the type of nucleotide. Hence, quenching of the already weak fluorescence was observed with the purine bases, whereas the association of the cyclophane with pyrimidine bases TMP, TTP, and CMP resulted in a significant fluorescence light-up effect. Thus, it was demonstrated that the styrylpyridine unit is a useful and complementary fluorophore for the development of selective nucleotide-targeting fluorescent probes based on alkylamine-linked cyclophanes. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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17 pages, 3847 KiB

Open AccessArticle

A Pathway for Aldol Additions Catalyzed by l-Hydroxyproline-Peptides via a β-Hydroxyketone Hemiaminal Intermediate

by Lo’ay Ahmed Al-Momani, Heinrich Lang and Steffen Lüdeke

Chemistry 2023, 5(2), 1203-1219; https://doi.org/10.3390/chemistry5020081 - 10 May 2023

Cited by 1 | Viewed by 1962

Abstract

While the use of l-proline-derived peptides has been proven similarly successful with respect to enantioselectivity, the physico-chemical and conformational properties of these organocatalysts are not fully compatible with transition state and intermediate structures previously suggested for l-proline catalysis. l-Proline or [...] Read more.

While the use of l-proline-derived peptides has been proven similarly successful with respect to enantioselectivity, the physico-chemical and conformational properties of these organocatalysts are not fully compatible with transition state and intermediate structures previously suggested for l-proline catalysis. l-Proline or l-4-hydroxyproline catalysis is assumed to involve proton transfers mediated by the carboxylic acid group, whereas a similar mechanism is unlikely for peptides, which lack a proton donor. Herein, we prepared an array of hydroxyproline-based dipeptides through amide coupling of Boc-protected cis- or trans-4-l-hydroxyproline (cis- or trans-4-Hyp) to benzylated glycine (Gly-OBn) and l-valine (l-Val-OBn) and used these dipeptides as catalysts for a model aldol reaction. Despite the lack of a proton donor in the catalytic site, we observed good stereoselectivities for the R-configured aldol product both with dipeptides formed from cis- or trans-4-Hyp at moderate conversions after 24 h. To explain this conundrum, we modeled reaction cycles for aldol additions in the presence of cis-4-Hyp, trans-4-Hyp, and cis- and trans-configured 4-Hyp-peptides as catalysts by calculation of free energies of conformers of intermediates and transition states at the density functional theory level (B3LYP/6-31G(d), DMSO PCM as solvent model). While a catalytic cycle as previously suggested with l-proline is also plausible for cis- or trans-4-Hyp, with the peptides, the energy barrier of the first reaction step would be too high to allow conversions at room temperature. Calculations on modeled transition states suggest an alternative pathway that would explain the experimental results: here, the catalytic cycle is entered by the acetone self-adduct 4-hydroxy-4-methylpentan-2-one, which forms spontaneously to a small extent in the presence of a base, leading to considerably reduced calculated free energy levels of transition states of reaction steps that are considered rate-determining. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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19 pages, 1104 KiB

Open AccessArticle

Platform Chemicals from Ethylene Glycol and Isobutene: Thermodynamics “Pays” for Biomass Valorisation and Acquires “Cashback”

by Sergey P. Verevkin and Aleksandra A. Zhabina

Chemistry 2023, 5(2), 1171-1189; https://doi.org/10.3390/chemistry5020079 - 9 May 2023

Viewed by 2133

Abstract

Ethylene glycol (EG) produced from biomass is a promising candidate for several new applications. In this paper, EG derivatives such as mono- and di-tert-butyl ethers are considered. However, accurate thermodynamic data are essential to optimise the technology of the direct tert-butyl ether EG [...] Read more.

Ethylene glycol (EG) produced from biomass is a promising candidate for several new applications. In this paper, EG derivatives such as mono- and di-tert-butyl ethers are considered. However, accurate thermodynamic data are essential to optimise the technology of the direct tert-butyl ether EG synthesis reaction or reverse process isobutene release. The aim of this work is to measure the vapour pressures and combustion energies for these ethers and determine the vaporisation enthalpies and enthalpies of formation from these measurements. Methods based on the First and Second Law of Thermodynamics were combined to discover the reliable thermodynamics of ether synthesis reactions. The thermochemical data for ethylene glycol tert-butyl ethers were validated using structure–property correlations and quantum chemical calculations. The literature results of the equilibrium study of alkylation of EG with isobutene were evaluated and the thermodynamic functions of ethylene glycol tert-butyl ethers were derived. The energetics of alkylation determined according to the “First Law” and the “Second Law” methods agree very well. Some interesting aspects related to the entropy of ethylene glycol tert-butyl ethers were also revealed and discussed. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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14 pages, 8666 KiB

Open AccessArticle

Activated Carbon from Sugarcane Bagasse: A Low-Cost Approach towards Cr(VI) Removal from Wastewater

by Rana Ahmed, Inga Block, Fabian Otte, Christina Günter, Alysson Duarte-Rodrigues, Peter Hesemann, Amitabh Banerji and Andreas Taubert

Chemistry 2023, 5(2), 1124-1137; https://doi.org/10.3390/chemistry5020077 - 9 May 2023

Viewed by 2996

Abstract

The potential of pretreated sugarcane bagasse (SCB) as a low-cost and renewable source to yield activated carbon (AC) for chromate CrO₄²⁻ removal from an aqueous solution has been investigated. Raw sugarcane bagasse was pretreated with H₂SO₄, H [...] Read more.

The potential of pretreated sugarcane bagasse (SCB) as a low-cost and renewable source to yield activated carbon (AC) for chromate CrO₄²⁻ removal from an aqueous solution has been investigated. Raw sugarcane bagasse was pretreated with H₂SO₄, H₃PO₄, HCl, HNO₃, KOH, NaOH, or ZnCl₂ before carbonization at 700 °C. Only pretreatments with H₂SO₄ and KOH yield clean AC powders, while the other powders still contain non-carbonaceous components. The point of zero charge for ACs obtained from SCB pretreated with H₂SO₄ and KOH is 7.71 and 2.62, respectively. Batch equilibrium studies show that the most effective conditions for chromate removal are a low pH (i.e., below 3) where >96% of the chromate is removed from the aqueous solution. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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17 pages, 4177 KiB

Open AccessArticle

Surface Functionalization of Calcium Phosphate Nanoparticles via Click Chemistry: Covalent Attachment of Proteins and Ultrasmall Gold Nanoparticles

by Kathrin Kostka and Matthias Epple

Chemistry 2023, 5(2), 1060-1076; https://doi.org/10.3390/chemistry5020072 - 7 May 2023

Cited by 4 | Viewed by 2524

Abstract

Calcium phosphate nanoparticles (60 nm) were stabilized with either polyethyleneimine (PEI; polycationic electrolyte) or carboxymethylcellulose (CMC; polyanionic electrolyte). Next, a silica shell was added and terminated with either azide or alkyne groups via siloxane coupling chemistry. The particles were covalently functionalized by copper-catalyzed [...] Read more.

Calcium phosphate nanoparticles (60 nm) were stabilized with either polyethyleneimine (PEI; polycationic electrolyte) or carboxymethylcellulose (CMC; polyanionic electrolyte). Next, a silica shell was added and terminated with either azide or alkyne groups via siloxane coupling chemistry. The particles were covalently functionalized by copper-catalyzed azide-alkyne cycloaddition (CuAAC; click chemistry) with proteins or gold nanoparticles that carried the complementary group, i.e., either alkyne or azide. The model proteins hemoglobin and bovine serum albumin (BSA) were attached as well as ultrasmall gold nanoparticles (2 nm). The number of protein molecules and gold nanoparticles attached to each calcium phosphate nanoparticle was quantitatively determined by extensive fluorescent labelling and UV–Vis spectroscopy on positively (PEI) or negatively (CMC) charged calcium phosphate nanoparticles, respectively. Depending on the cargo and the nanoparticle charge, this number was in the range of several hundreds to thousands. The functionalized calcium phosphate particles were well dispersible in water as shown by dynamic light scattering and internally amorphous as shown by X-ray powder diffraction. They were easily taken up by HeLa cells and not cytotoxic. This demonstrates that the covalent surface functionalization of calcium phosphate nanoparticles is a versatile method to create transporters with firmly attached cargo molecules into cells. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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18 pages, 3405 KiB

Open AccessArticle

Synthesis, Structures and Photophysical Properties of Tetra- and Hexanuclear Zinc Complexes Supported by Tridentate Schiff Base Ligands

by Tobias Severin, Viktoriia Karabtsova, Martin Börner, Hendrik Weiske, Agnieszka Kuc and Berthold Kersting

Chemistry 2023, 5(2), 1028-1045; https://doi.org/10.3390/chemistry5020070 - 2 May 2023

Cited by 1 | Viewed by 2469

Abstract

The synthesis, structure and photophysical properties of two polynuclear zinc complexes, namely [Zn₆L₂(µ₃-OH)₂(OAc)₈] (1) and [Zn₄L₄(µ₂-OH)₂](ClO₄)₂ (2 [...] Read more.

The synthesis, structure and photophysical properties of two polynuclear zinc complexes, namely [Zn₆L₂(µ₃-OH)₂(OAc)₈] (1) and [Zn₄L₄(µ₂-OH)₂](ClO₄)₂ (2), supported by tridentate Schiff base ligand 2,6-bis((N-benzyl)iminomethyl)-4-tert-butylphenol (HL) are presented. The synthesized compounds were investigated using ESI-MS, IR, NMR, UV-vis absorption spectroscopy, photoluminescence spectroscopy and single-crystal X-ray crystallography. The hexanuclear neutral complex 1 comprises six-, five- and four-coordinated Zn²⁺ ions coordinated by O and N atoms from the supporting ligand and OH- and acetate ligands. The Zn²⁺ ions in complex cation [Zn₄L₄(µ₂-OH)₂]²⁺ of 2 are all five-coordinated. The complexation of ligand HL by Zn²⁺ ions leads to a six-fold increase in the intensity and a large blue shift of the ligand-based ¹(π-π)* emission. Other biologically relevant ions, i.e., Na⁺, K⁺, Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺ and Cu²⁺, did not give rise to a fluorescence enhancement. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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22 pages, 6971 KiB

Open AccessArticle

Divalent Europium, NIR and Variable Emission of Trivalent Tm, Ho, Pr, Er, Nd, and Ce in 3D Frameworks and 2D Networks of Ln–Pyridylpyrazolates

by Heba Youssef, Jonathan Becker, Clemens Pietzonka, Ilya V. Taydakov, Florian Kraus and Klaus Müller-Buschbaum

Chemistry 2023, 5(2), 1006-1027; https://doi.org/10.3390/chemistry5020069 - 28 Apr 2023

Cited by 1 | Viewed by 2315

Abstract

The redox reactions of various lanthanide metals with 3-(4-pyridyl)pyrazole (4-PyPzH) or 3-(3-pyridyl)pyrazole (3-PyPzH) ligands yield the 2D network

_{\infty}^{2}

[Eu(4-PyPz)₂(Py)₂] containing divalent europium, the 3D frameworks

_{\infty}^{3}

[Ln(4-PyPz)₃] and

_{\infty}^{3}

[Ln(3-PyPz)₃] for [...] Read more.

The redox reactions of various lanthanide metals with 3-(4-pyridyl)pyrazole (4-PyPzH) or 3-(3-pyridyl)pyrazole (3-PyPzH) ligands yield the 2D network

_{\infty}^{2}

[Eu(4-PyPz)₂(Py)₂] containing divalent europium, the 3D frameworks

_{\infty}^{3}

[Ln(4-PyPz)₃] and

_{\infty}^{3}

[Ln(3-PyPz)₃] for trivalent cerium, praseodymium, neodymium, holmium, erbium, and thulium as well as

_{\infty}^{3}

[La(4-PyPz)₃], and the 2D networks

_{\infty}^{2}

[Ln(4-PyPz)₃(Py)] for trivalent cerium and thulium and

_{\infty}^{2}

[Ln₂(4-PyPz)₆]·Py for trivalent ytterbium and lutetium. The 18 lanthanide coordination polymers were synthesized under solvothermal conditions in pyridine (Py), partly acting as a co-ligand for some networks. The compounds exhibit a variety of luminescence properties, including metal-centered 4f–4f/5d–4f emission in the visible and near-infrared spectral range, metal-to-ligand energy transfer, and ligand-centered fluorescence and phosphorescence. The anionic ligands 3-PyPz⁻ and 4-PyPz⁻ serve as suitable antennas for lanthanide-based luminescence in the visible and near-infrared range through effective sensitization followed by emission through intra–4f transitions of the trivalent thulium, holmium, praseodymium, erbium, and neodymium.

_{\infty}^{2}

[Ce(4-PyPz)₃(Py)],

_{\infty}^{3}

[Ce(4-PyPz)₃], and

_{\infty}^{3}

[Ce(3-PyPz)₃] exhibit strong degrees of reduction in the 5d excited states that differ in intensity compared to the ligand-based emission, resulting in a distinct emission ranging from pink to orange. The direct current magnetic studies show magnetic isolation of the lanthanide centers in the crystal lattice of

_{\infty}^{3}

[Ln(3-PyPz)₃], Ln = Dy, Ho, and Er. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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13 pages, 3094 KiB

Open AccessArticle

Synthesis, Structure, and Spectroscopic Properties of Luminescent Coordination Polymers Based on the 2,5-Dimethoxyterephthalate Linker

by Aimée E. L. Cammiade, Laura Straub, David van Gerven, Mathias S. Wickleder and Uwe Ruschewitz

Chemistry 2023, 5(2), 965-977; https://doi.org/10.3390/chemistry5020065 - 22 Apr 2023

Cited by 1 | Viewed by 1930

Abstract

We report on the synthesis and the crystal structure of the solvent-free coordination polymer Co^II(2,5-DMT) (1) with 2,5-DMT ≡ 2,5-dimethoxyterephthalate which is isostructural to the already reported Mn^II and Zn^II congeners (C2/c, Z [...] Read more.

We report on the synthesis and the crystal structure of the solvent-free coordination polymer Co^II(2,5-DMT) (1) with 2,5-DMT ≡ 2,5-dimethoxyterephthalate which is isostructural to the already reported Mn^II and Zn^II congeners (C2/c, Z = 4). In contrast, for M = Mg^II, a MOF with DMF-filled pores is obtained, namely Mg₂(2,5-DMT)₂(DMF)₂ (2) (P

\bar{1}

, Z = 2). Attempts to remove these solvent molecules to record a gas sorption isotherm did not lead to meaningful results. In a comparative study, the thermal (DSC/TGA) and luminescence properties of all the four compounds were investigated. The compounds of the M^II(2,5-DMT) composition show high thermal stability up to more than 300 °C, with the Zn^II compound having the lowest decomposition temperature. M^II(2,5-DMT) with M^II = Mn^II, Zn^II and 2 show a bright luminescence upon blue light irradiation (λ = 405 nm), whereas Co^II in 1 quenches the emission. While Zn^II in Zn^II(2,5-DMT) and Mg^II in 2 do not significantly influence the (blue) emission and excitation bands compared to the free 2,5-DMT ligand, Mn^II in Mn^II(2,5-DMT) shows an additional metal-centred red emission. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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17 pages, 5683 KiB

Open AccessArticle

Synthesis of 5-Metalla-Spiro[4.5]Heterodecenes by [1,4]-Cycloaddition Reaction of Group 13 Diyls with 1,2-Diketones

by Hanns M. Weinert, Christoph Wölper and Stephan Schulz

Chemistry 2023, 5(2), 948-964; https://doi.org/10.3390/chemistry5020064 - 20 Apr 2023

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Abstract

Monovalent group 13 diyls are versatile reagents in oxidative addition reactions. We report here [1,4]-cycloaddition reactions of β-diketiminate-substituted diyls LM (M = Al, Ga, In, Tl; L = HC[C(Me)NDipp]₂, Dipp = 2,6-ⁱPr₂C₆H₃) with [...] Read more.

Monovalent group 13 diyls are versatile reagents in oxidative addition reactions. We report here [1,4]-cycloaddition reactions of β-diketiminate-substituted diyls LM (M = Al, Ga, In, Tl; L = HC[C(Me)NDipp]₂, Dipp = 2,6-ⁱPr₂C₆H₃) with various 1,2-diketones to give 5-metalla-spiro[4.5]heterodecenes 1, 4–6, and 8–10, respectively. In contrast, the reaction of LTl with acenaphthenequinone gave the [2,3]-cycloaddition product 7, with Tl remaining in the +1 oxidation state. Compound 1 also reacted with a second equivalent of butanedione as well as with benzaldehyde in aldol-type addition reactions to the corresponding α,β-hydroxyketones 2 and 3, while a reductive activation of a benzene ring was observed in the reaction of benzil with two equivalents of LAl to give the 1,4-aluminacyclohex-2,4-dien 12. In addition, the reaction of L’BCl₂ (L = HC[C(Me)NC₆F₅]₂) with one equivalent of benzil in the presence of KC₈ gave the corresponding 5-bora-spiro[4.5]heterodecene 13, whereas the hydroboration reaction of butanedione with L’BH₂ (14), which was obtained from the reaction of L’BCl₂ with L-selectride, failed to give the saturated 5-bora-spiro[4.5]heterodecane. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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14 pages, 4517 KiB

Open AccessArticle

Stabilization of 2-Pyridyltellurium(II) Derivatives by Oxidorhenium(V) Complexes

by Felipe Dornelles da Silva, Maximilian Roca Jungfer, Adelheid Hagenbach, Ernesto Schulz Lang and Ulrich Abram

Chemistry 2023, 5(2), 934-947; https://doi.org/10.3390/chemistry5020063 - 18 Apr 2023

Cited by 1 | Viewed by 1638

Abstract

Zwitterionic compounds such as pyridine-containing tellurenyl compounds are interesting building blocks for heterometallic assemblies. They can act as ambiphilic donor/acceptors as is shown by the products of reactions of the zwitterions HpyTeCl₂ or HCF₃pyTeCl₂ with the rhenium(V) complex [ReOCl [...] Read more.

Zwitterionic compounds such as pyridine-containing tellurenyl compounds are interesting building blocks for heterometallic assemblies. They can act as ambiphilic donor/acceptors as is shown by the products of reactions of the zwitterions HpyTeCl₂ or HCF₃pyTeCl₂ with the rhenium(V) complex [ReOCl₃(PPh₃)₂]. The products have a composition of [ReO₂Cl(pyTeCl)(PPh₃)₂] and [ReO₂Cl(CF₃pyTeCl)(PPh₃)₂] with central

{O = R \overset{⏠}{e = O \dots Te (Cl) p} y}^{+}

units. The Re-O bonds in the products are elongated by approximately 0.1 Å compared with those to the terminal oxido ligands and establish Te…O contacts. Thus, the normally easily assigned concept of oxidation states established at the two metal ions becomes questionable (Re^V/Te^II vs. Re^III/Te^IV). A simple bond length consideration rather leads to a description with the coordination of a mesityltellurenyl(II) chloride unit to an oxido ligand of the Re(V) center, but the oxidation of the tellurium ion and the formation of a tellurinic acid chloride cannot be ruled out completely from an analysis of the solid-state structures. DFT calculations (QTAIM, NBO analysis) give clear support for the formation of a Re(V) dioxide complex donating into an organotellurium(II) chloride and the alternative description can at most be regarded as a less favored resonance structure. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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22 pages, 5871 KiB

Open AccessArticle

Phosphine Functionalized Cp^C Ligands and Their Metal Complexes

by Florian Nährig, Yu Sun and Werner R. Thiel

Chemistry 2023, 5(2), 912-933; https://doi.org/10.3390/chemistry5020062 - 18 Apr 2023

Viewed by 1650

Abstract

Simple nucleophilic aliphatic substitution gives access to mono- and diphosphine ligands with a Cp^C group in the backbone. The monophosphine ligand coordinates to gold(I) via the phosphine site, to thallium(I) via the cyclopentadienyl site and to ruthenium(II) via a combination of both, [...] Read more.

Simple nucleophilic aliphatic substitution gives access to mono- and diphosphine ligands with a Cp^C group in the backbone. The monophosphine ligand coordinates to gold(I) via the phosphine site, to thallium(I) via the cyclopentadienyl site and to ruthenium(II) via a combination of both, resulting in an ansa-type structure. Coordination with the cyclopentadiene site is not possible for the diphosphine ligand. In this case, monodentate coordination to gold(I) and bidentate coordination to the [PdCl(μ²-Cl)]₂, the [Rh(CO)(μ²-Cl)]₂, and the Rh(CO)Cl fragment is observed, showing the variability in coordination modes possible for the long-chain diphosphine ligand. Ligands and complexes were characterized by means of NMR and IR spectroscopy, elemental analysis and X-ray structure analysis. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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21 pages, 6573 KiB

Open AccessArticle

Coinage Metal Complexes Containing Perfluorinated Carboxylates

by Robin Piani, Björn B. Beele, Jörg Rust, Christian W. Lehmann and Fabian Mohr

Chemistry 2023, 5(2), 813-833; https://doi.org/10.3390/chemistry5020058 - 8 Apr 2023

Cited by 1 | Viewed by 1611

Abstract

A variety of coinage-metal complexes containing perfluorinated carboxylate ligands, together with their structures and thermal behavior, are reported. The silver(I) salts were accessible from the direct reaction of Ag₂O with the acids in toluene. Their gold(I) phosphine counterparts formed in high [...] Read more.

A variety of coinage-metal complexes containing perfluorinated carboxylate ligands, together with their structures and thermal behavior, are reported. The silver(I) salts were accessible from the direct reaction of Ag₂O with the acids in toluene. Their gold(I) phosphine counterparts formed in high yields by transmetallation using the silver(I) salts. Some structurally unique, mixed-metal (Au,Ag) complexes formed upon combining solutions of the silver(I) salts with the gold(I) phosphine carboxylates. The reduction of dinuclear copper(II) compounds containing perfluorinated carboxylates with triphenylphosphine resulted in the formation of the corresponding copper(I) tris(phosphine) complexes. X-ray structures of representative complexes, together with IR- and TGA data, are reported. Full article

(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)

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