Antimicrobial Properties of Amino-Acid-Derived N-Heterocyclic Carbene Silver Complexes

Complexes {Ag[NHC^Mes,R]}_n (R = H, 2a; Me, 2b and 2b’; ⁱPr, 2c; ⁱBu, 2d), were prepared by treatment of imidazolium precursor compounds [Im^Mes,R] (2-(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a, (S)-2-alkyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1b–d, and (R)-2-methyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1b’, with Ag₂O under appropriate conditions. They were characterised by analytical, spectroscopic (IR, ¹H, and ¹³C NMR and polarimetry), and X-ray methods (2a). In the solid state, 2a is a one-dimensional coordination polymer, in which the silver(I) cation is bonded to the carbene ligand and to the carboxylate group of a symmetry-related Ag[NHC^Mes,H] moiety. The coordination environment of the silver centre is well described by the DFT study of the dimeric model {Ag[NHC^Mes,H]}₂. The antimicrobial properties of these complexes were evaluated versus Gram-negative bacteria E. coli and P. aeruginosa. From the observed MIC and MBC values (minimal inhibitory concentration and minimal bactericidal concentration, respectively), complex 2b’ showed the best antimicrobial properties (eutomer), which were significantly better than those of its enantiomeric derivative 2b (distomer). Additionally, analysis of MIC and MBC values of 2a–d reveal a clear structure–antimicrobial effect relationship. Antimicrobial activity decreases when the steric properties of the R alkyl group in {Ag[NHC^Mes,R]}_n increase.

Homochiral imidazolium-based dicarboxylate silver(I) compounds: synthesis, characterisation and antimicrobial properties

Complexes [Ag(LR)], 2 (LR = 2,2'-(imidazolium-1,3-diyl)di(2-alkylacetate)), were prepared by treatment of compounds HLR, 1, with Ag2O. They were characterised by analytical, spectroscopic (IR, 1H and 13C NMR and polarimetry) and...

N-Heterocyclic carbenes and their precursors in functionalised porous materials

Though N-heterocyclic carbenes (NHCs) have emerged as diverse and powerful discrete functional molecules in pharmaceutics, nanotechnology, and catalysis over decades, the heterogenization of NHCs and their precursors for broader applications in porous materials, like metal-organic frameworks (MOFs), porous coordination polymers (PCPs), covalent-organic frameworks (COFs), porous organic polymers (POPs), and porous organometallic cages (POMCs) was not extensively studied until the last ten years. By de novo or post-synthetic modification (PSM) methods, myriads of NHCs and their precursors containing building blocks were designed and integrated into MOFs, PCPs, COFs, POPs and POMCs to form various structures and porosities. Functionalisation with NHCs and their precursors significantly expands the scope of the potential applications of porous materials by tuning the pore surface chemical/physical properties, providing active sites for binding guest molecules and substrates and realizing recyclability. In this review, we summarise and discuss the recent progress on the synthetic methods, structural features, and promising applications of NHCs and their precursors in functionalised porous materials. At the end, a brief perspective on the encouraging future prospects and challenges in this contemporary field is presented. This review will serve as a guide for researchers to design and synthesize more novel porous materials functionalised with NHCs and their precursors.

Synthesis and structural characterization of homochiral coordination polymers with imidazole-based monocarboxylate ligands

Chiral Na[(S)-L^R] (R = Me, 1a; ⁱPr, 1b; CH₂ⁱPr, 1c, and (S)-^secBu, 1d) and Na[(R)-L^R] (R = Me, 1a') compounds were synthesised following standard procedures. New compounds 1d and 1a' were analytically and spectroscopically characterised. 1a and 1c were structurally identified by single-crystal X-ray diffraction methods as homochiral 2D coordination polymers, {Na(H₂O)[(S)-L^Me]}_n and {Na[(S)-L^CH₂iPr]}_n, respectively. Both (S)-2alkyl,2-(1H-imidazol-1-yl)acetate anions displayed unprecedented coordination modes in these coordination polymers: μ₃κ²OκO' for 1a and μ₄κ²Oκ²O' for 1c. Enantiomeric species 1a', {Na(H₂O)[(R)-L^Me]}_n, showed the same X-ray powder diffractogram (XRPD) as 1a, in agreement with a similar crystal structure. DFT calculations on the [L^R]^- anions confirmed their coordination capabilities as ditopic linkers. In fact, the reaction of Na[L^R] with several metal salts yielded the following coordination polymers: {Ag[(S)-L^Me]}_n, 2a, {Ag[(R)-L^Me]}_n, 2a', {Cu[(S)-L^R]₂}_n (R = Me, 3a; ⁱPr, 3b), {Cu[(R)-L^Me]}_n, 3a', {Zn[(S)-L^R]₂}_n (R = Me, 4a; ⁱPr, 4b; (S)-^secBu, 4d) and {Zn[(R)-L^Me]₂}_n, 4a'. For the known compounds 3a and 4a, this procedure is a new synthetic route that avoided high temperature reaction conditions. New complexes 2, 3a', b, and 4a', b, d were characterised by elemental analysis, infrared and XRPD methods and complex 2a by single-crystal X-ray diffraction. This complex is also a two-dimensional coordination polymer in which the [(S)-L^Me]^- anion acts as a μ₄κN,κ²O,κ²O' bridging ligand. Compounds 1-4a' are the first examples of homochiral coordination polymers with imidazole-monocarboxylate ligands based on non-natural amino acids. Preliminary studies on the metal-catalysed preparation of chiral α-aminophosphonates were carried out but, unfortunately, no enantioselectivity was observed.

Synthesis and structural characterization of homochiral 2D coordination polymers of zinc and copper with conformationally flexible ditopic imidazolium-based dicarboxylate ligands

Chiral imidazolium-based dicarboxylate ligands behave as bridging ditopic linkers capable of forming 2D coordination polymers with zinc and copper metals.

Controllable assembly of Cu(ii) coordination compounds based on a flexible zwitterionic benzimidazole–dicarboxylate ligand: synthesis, structural diversity, reversible SCSC transformation and magnetic properties

The reversible SCSC transformation of a paddle-wheel cluster to a 1D linear polymer could be accomplished.

Photoluminescent calcium azolium carboxylates with diversified calcium coordination geometry and thermal stability

Six new luminescent calcium coordination assemblies were successfully synthesized and characterized using bis- and tris-azolium carboxylic acid ligands.

Bis(4-pyridyl)mercury – a new linear tecton in crystal engineering: coordination polymers and co-crystallization processes

Three new coordination polymers have been obtained using bis(4-pyridyl)mercury (py₂Hg) as a spacer: [Cu(Hmea)₂(py₂Hg)](ClO₄)₂·2(py₂Hg) (1), [Cu₂(pa)₂(py₂Hg)(ClO₄)₂]·0.5(py₂Hg)·H₂O (2), and [Cu₂(pa)₂(py₂Hg)₂](BF₄)₂ (3) (Hmea = monoethanolamine; Hpa = propanolamine).

Synthesis of new copper(i) based linear 1-D-coordination polymers with neutral imidazolinium-dithiocarboxylate ligands

An imidazolinium-dithiocarboxylate betaine has been applied for the first time as a ligand in a coordination polymer with copper(i) halides.