Statistical Analysis of Noncovalent Interactions of Anion Groups in Crystal Structures. III. Metal Complexes of Thiocyanate and their Hydrogen-Donor Accepting Function

Abstract

The bidentate function of the thiocyanate anion was studied using the Cambridge Structural Database System. Complexing properties (metal–thiocyanate interactions) with respect to metal cations were analysed. Two main classes were distinguished: (a) alkali and alkaline earth metals, and (b) metals of Zn and Cu groups and transition metals (group VIII). Good correlations were found between the nature of the metal (radius, oxidation state and charge) and its position relative to the thiocyanate unit. Hydrogen-bond acceptor properties of discrete and complexed SCN units were compared. The extraordinarily active hydrogen-bonding behaviour allows this anion to act as a powerful bridge between different molecular fragments. In metal complexes the cation provokes a redistribution of anionic charge in SCN and the distribution of electron density, in turn, controls the hydrogen-bonding properties of the terminal acceptor atom. Binding properties of thiocyanate in biological systems were illustrated using the Brookhaven Protein Data Bank. A comparison of anion binding in small-molecule structures and in macromolecular structures shows good agreement.