STATISTICAL-ANALYSIS OF NONCOVALENT INTERACTIONS OF ANION GROUPS IN CRYSTAL-STRUCTURES - III - METAL-COMPLEXES OF THIOCYANATE AND THEIR HYDROGEN-DONOR ACCEPTING FUNCTION

The bidentate function of the thiocyanate anion was studied using the Cambridge Structural Database System. Complexing properties (metal-thi ocyanate interactions) with respect to metal cations were analysed. Tw o main classes were distinguished: (a) alkali and alkaline earth metal s, and (b) metals of Zn and Cu groups and transition metals (group VII I). Good correlations were found between the nature of the metal (radi us, oxidation state and charge) and its position relative to the thioc yanate unit. Hydrogen-bond acceptor properties of discrete and complex ed SCN units were compared. The extraordinarily active hydrogen-bondin g behaviour allows this anion to act as a powerful bridge between diff erent molecular fragments. In metal complexes the cation provokes a re distribution of anionic charge in SCN and the distribution of electron density, in turn, controls the hydrogen-bonding properties of the ter minal acceptor atom. Binding properties of thiocyanate in biological s ystems were illustrated using the Brookhaven Protein Data Bank. A comp arison of anion binding in small-molecule structures and in macromolec ular structures shows good agreement.