Beschreibung:
<jats:p>The well-known ambidentate nature of the thiocyanate ion is exemplified by its complexes with the Group IIb metal cations, in which zinc tends to be N bonded, mercury to be S bonded, and cadmium, a borderline case, has been shown to be bridged in aqueous solution (Cd–NCS–Cd). An investigation was initiated in order to more closely study the aqueous zinc/thiocyanate system, in particular to see if zinc can be induced to show either a change in bonding preference or bridging. Raman spectroscopy combined with the method of continuous variations was used to study a series of aqueous zinc thiocyanate solutions in which the ratio (R) of thiocynate to zinc was varied from 0.25 to 9. Under these conditions, there is no spectroscopic evidence for bridging thiocyanate ions or for a change in the bonding preferences of zinc. However, the results obtained were consistent with the existence of four distinct complex species corresponding to the mono-, di-, tri-, and tetra-substituted zinc ion. Furthermore, there is strong evidence that the two lower species are octahedrally coordinated with water as the other ligand while the higher species are tetrahedral. Comparison of spectra from the C–N stretching region of aqueous solutions with high R values [where the Zn(NCS)42− species is predominant] with similar spectra of Zn(NCS)42− in organic solvents reveals that the A1 mode in aqueous solutions is more intense than the F2 stretching mode while the converse is true in the organic systems. If the additivity of bond polarizabilities were rigorously obeyed, this reversal of intensities would not be expected. In certain cases this type of behavior has been explained by means of the resonance Raman effect. However, this does not seem to be the explanation in the present case.</jats:p>