Certain Interactions between Transition Metal Ions and the NCS Group in Chromium(III) Isothiocyanato Complexes. I. Reinecke’s Salt Type Complexes Involving Cobalt(II) and Copper(II) Ions

Abstract

Abstract Cobalt(II) tetraisothiocyanatochromate(III), Co[Cr(NCS)4(NH3)2]2, was prepared from cobalt(II) chloride and Reinecke’s salt in an aqueous solution. The absorption spectrum gave evidence that the so-called “cobalt-salt” dissociated into cobalt(II) cation and Reineck’s anion in aqueous solution. The reflection spectrum showed a remarkably strong absorption band at 14.08×1013 sec−1, which might be assigned to bonding between cobalt(II) and sulfur in an NCS− ligand. The three absorption peaks observed at 2158, 2095 and 2065 cm−1 in the IR spectrum due to C–N stretching vibrations also emphasized the strong interaction between cobalt and sulfur. The effective magnetic moment estimated was 4.58 B. M. at 18.3°C. The corresponding copper(II) salt, Cu(OH)[Cr(NCS)4(NH3)2], was obtained from an aqueous solution of copper(II) sulfate and Reinecke’s salt as a yellow powder. It was a sparingly soluble in water. In the reflection spectrum, the red-shifted band covered much of the first band region of Reinecke’s salt and in the IR spectrum, the C–N band had only a small splitting. The magnetic moment was found to be 3.84 B. M. at 16.0°C, which is close to the predicted value in the complex when copper is reduced, becoming univalent. X-Ray diffraction analysis also showed a relatively stronger contraction of the unit cell in the copper salt than in the cobalt salt. On the basis of the above points, it was proposed that in the copper salt there is considerable π-bonding between copper and the two adjacent isothiocyanate groups.