Statistical analysis of noncovalent interactions of anion groups in crystal structures. II. Hydrogen bonding of thiocyanate anions

The hydrogen-bond acceptor function of the thiocyanate anion is analyzed in 52 crystal structures retrieved from the Cambridge Crystallographic Database. All modes of hydrogen-bond coordination are represented: by the sulfur, by the nitrogen and by the π-system of the anion. The preferred areas for the H donors (D = OH and NH groups) were determined: (a) around sulfur, as a torus centered at the S end, the axis of which is the linear anion, and with an average DSON angle of 99°, and (b) around nitrogen, on a spherical cap delimited by the solid angle, SOND (average = 145°), with the linear anion. The anion-acceptor function is characterized by multiple hydrogen bonding and, in most cases (80%), thiocyanate binds through both acceptor centers (S and N). Important backbonding of sulfur in the thiocyanate anion is structurally evidenced.