Hydrogen bonding between metal hydroxides and common organic functional groups was investigated using density functional theory (DFT) calculations. Copper and aluminum hydroxides were used to represent metal hydroxides. Methylamine, methanimine, imidazole, methanole, ethanal, methanethiol and dimehylphosphinic acid were selected as common organic molecules. We performed calculations on the complexes between selected molecules and a water molecule to obtain benchmark hydrogen bond strengths and determine their donor and acceptor abilities. Then we carried out calculations with a simple model of a discrete cluster for copper and aluminum hydroxides. Our results showed that copper hydroxide has better donor and acceptor abilities than a water molecule but aluminum hydroxide form hydrogen bonds with similar properties as a water molecule. Among all organic molecules usen in this study, imidazole and dimethylphosphinic acid formed the strongest hydrogen bonds both as donor and acceptor. Many complexes showed the formation of bonds where a CH group acted as a donor, therefore we also analyzed the dependence of the energy on bond lengths and their angles.
To assess whether simple discrete cluster model gives reasonable results for metal hydroxide systems, we also performed calculations on the metal hydroxide surfaces, which were represented by a periodic slab model. Only imidazole and dimethylphosphinic acid molecules were adsorbed on the surface because they formed the strongest hydrogen bonds with discrete clusters. A comparison of both models showed that the energies of adsorption could be estimated with discrete cluster calculations, but only under provision that one can predict the geometry of bonding and the number of formed hydrogen bonds.
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