School of Chemistry - Research Publications
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ItemElectrical conductivity and DFT investigations of a 2D CuI-TCNQII− framework(Royal Society of Chemistry, 2023-11-21)A stacked 2D Cu(i) coordination polymer displays electrical conductivity with DFT calculations revealing a band structure comprised of donor TCNQII− and acceptor 2,5-dimethylpyrazine p-orbitals.
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ItemComplexes of 2,4,6-trihydroxybenzoic acid: effects of intramolecular hydrogen bonding on ligand geometry and metal binding modes(INT UNION CRYSTALLOGRAPHY, 2022-11)This article describes a series of more than 20 new compounds formed by the combination of 2,4,6-trihydroxybenzoic acid (H4thba) with metal ions in the presence of a base, with structures that include discrete molecular units, chains, and two- and three-dimensional networks. As a result of the presence of two ortho-hydroxy groups, H4thba is a relatively strong acid (pKa1 = 1.68). The carboxylate group in H3thba- is therefore considerably less basic than most carboxylates with intramolecular hydrogen bonds, conferring a rigid planar geometry upon the anion. These characteristics of H3thba- significantly impact upon the way it interacts with metal ions. In s-block metal compounds, where the interaction of the metal centres with the carboxylate O atoms is essentially ionic, the anion bonds to up to three metal centres via a variety of binding modes. In cases where the metal ion is able to form directional coordinate bonds, however, the carboxylate group tends to bond in a monodentate mode, interacting with just one metal centre in the syn mode. A dominant influence on the structures of the complexes seems to be the face-to-face stacking of the aromatic rings, which creates networks containing layers of metal-oxygen polyhedra that participate in hydrogen bonding. This investigation was undertaken, in part, by a group of secondary school students as an educational exercise designed to introduce school students to the technique of single-crystal X-ray diffraction and enhance their understanding of primary and secondary bonding.
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ItemNo Preview AvailableSynthesis, structure and properties of coordination polymers formed from bridging 4-hydroxybenzoic acid anions(ROYAL SOC CHEMISTRY, 2022-03-07)The combination of 4-hydroxbenzoic acid with metal ions Li+, Mg2+ and Cu2+ leads to the formation of novel 2D and 3D networks.
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ItemThe elusive crystals of calcium acetate hemihydrate: chiral rods linked by parallel hydrophilic strips(Royal Society of Chemistry, 2021-01-21)Calcium acetate hemihydrate is found in the efflorescent salts that form on pottery and other calcareous heritage artefacts. The formation of these salts can lead to deterioration of these objects. A recent analysis of the structure of Ca(OAc)2·½H2O by X-ray powder diffraction (XRPD) has revealed it has a remarkable and surprisingly complex structure. Although the compound usually exists in powder or microcrystalline form, often in mixtures with other salts, we have serendipitously managed to grow crystals of a size suitable for single crystal X-ray diffraction. Our single crystal data show the structure is based on infinite supramolecular polymeric rods that are chiral. Each rod has a minimum diameter of 1.75 nm and the external surface of each rod features four parallel, hydrophobic domains separated by hydrophilic strips. Each hydrophilic strip consists of acetate oxygen atoms and coordinated water molecules that are able to form hydrogen bonding interactions with symmetry-related strips on a neighbouring rod in an arrangement that resembles a zipper. Within the extended crystal structure each rod is bound to four rods of opposite handedness to give a racemic mixture.
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ItemAlkali metal salts of 4-hydroxybenzoic acid: a structural and educational study.(International Union of Crystallography, 2021-07-01)As part of an educational exercise designed to introduce school students to the technique of single-crystal X-ray diffraction and enhance their understanding of primary and secondary bonding, a group of nine secondary school students was given the opportunity to prepare new compounds and to solve and refine data collected on the crystalline materials they had prepared. Their investigation of the alkali metal salts of 4-hydroxybenzoic acid (H2hba) yielded nine new compounds and their structures are described in this article. Whilst the salts might be expected to have similar atomic arrangements, there are significant differences in their structures. Although H2hba is a relatively simple organic molecule, it displays remarkable coordinative flexibility, forming ionic solids containing the uncharged molecule, the monoanion Hhba- or the dianion hba2-. A common feature of the structures is their layered arrangement: alternating hydrophilic layers made up of closely packed metal-oxygen polyhedra separated by the hydrophobic component of the hydroxybenzoate linking units. Close packing of these units seems to be a dominant influence in determining the overall structure. The hydroxybenzoate units are usually both parallel and antiparallel with their immediate neighbours, with packing that can be edge-to-face, face-to-face or a mixture of the two. Hydrogen bonding plays a key role in the structure of most compounds and a short strong hydrogen bond (SSHB) is observed in two of the networks. The compounds of 4-hydroxybenzoic acid, C7H6O3, described here are: poly[di-μ-aqua-μ-4-oxidobenzoato-dilithium], [Li2(C7H4O3)(H2O)2]n, 1, poly[triaqua-μ-4-oxidobenzoato-dilithium], [Li2(C7H4O3)(H2O)3]n, 2, poly[μ-4-hydroxybenzoato-lithium], [Li(C7H5O3)]n, 3, catena-poly[4-hydroxybenzoate [[diaquasodium]-di-μ-aqua]], {[Na(H2O)4](C7H5O3)}n, 4, poly[di-μ-aqua-aqua-μ-4-hydroxybenzoato-potassium], [K(C7H5O3)(H2O)3]n, 5, poly[μ-aqua-μ-4-hydroxybenzoato-potassium], [K(C7H5O3)(H2O)]n, 6, poly[aqua-μ-4-hydroxybenzoato-rubidium], [Rb(C7H5O3)(H2O)]n, 7, poly[aqua-μ-4-hydroxybenzoato-caesium], [Cs(C7H5O3)(H2O)]n, 8, poly[[μ-aqua-aqua(μ-4-hydroxybenzoato)(4-hydroxybenzoic acid)sodium] monohydrate], {[Na(C7H5O3)(C7H6O3)(H2O)2]·H2O}n, 9, poly[[(μ-4-hydroxybenzoato)(μ-4-hydroxybenzoic acid)rubidium] monohydrate], {[K(C7H5O3)(C7H6O3)]·H2O}n, 10, and poly[[(μ-4-hydroxybenzoato)(μ-4-hydroxybenzoic acid)rubidium] monohydrate], {[Rb(C7H5O3)(C7H6O3)]·H2O}n, 11.