Magnetic properties of cobalt(II) complexes. Part I. Trigonally distorted octahedral geometries

Abstract

The theoretical behaviour of principal and average magnetic moments of octahedral cobalt(II) complexes perturbed by spin–orbit coupling and a D_3d symmetry crystal-field distortion is presented. Calculations were performed using a complete spin–quartet basis and the crystal-field parameterized by second- and fourth-order radial parameters Cp and Dq, and an angular parameter, θ. The behaviours of both average moments and anistropies are complex and depend markedly upon the magnitude of Cp.

Magnetic moments of hexakis(imidazole)cobalt(II) dinitrate, and hexa-aquocobalt(II) fluorosilicate and fluorogermanate as powders and crystals are reported in the temperature range 300–90 K. The results are compared with the theoretical model and give values of Cp as ≲1000 or ≳8000 cm^–1. Preference for the higher values illustrates an inverse relationship between Dq and Cp/Dq.

The single-crystal spectrum of the imidazole complex at 77 and 300 K is presented and compared with previous spectral work on the fluorosilicate.