New planar cobalt(II) and nickel(II) complexes

Abstract

Some planar complexes of cobalt(II) and nickel(II) derived from triazene 1-oxides are reported in this paper. The cobalt(II) complexes are very stable and are shown to be monomolecular in solution. Their magnetic moments lie in the range 2.08–2.19 BM. They show electronic spectra with many features in the range 4500–30,000 cm⁻¹. Probable assignment schemes are suggested on the basis of a strong field model. In one of these schemes the spectra of the cobalt(II) and nickel(II) complexes can be understood on the basis of a single set of crystal field and Slater-Condon parameters. In pyridine solution the cobalt(II) and nickel(II) species exist in equilibrium with high spin adducts. The thermodynamic parameters ΔH′ and ΔS′ for the equilibrium are determined for nickel(II) species from variable temperature magnetic data. It is shown that adduct formation is more exetensive in the case of cobalt(II) than in the case of nickel(II).