Electronic structure and magnetic properties of high-spin octahedral Co(II) complexes: Co(II)(acac)2(H2O)2Co(II)(acac)2(H2O)2

Abstract

An analysis of the electronic structure of the high-spin 3d73d7 Co(II) ion in the approximately octahedral Co(II)(acac)2(H2O)2Co(II)(acac)2(H2O)2 complex is presented in terms of crystal fields of descending symmetry from octahedral to orthorhombic. The energies and wave functions resulting from the interplay of these fields with the spin–orbit coupling are used to obtain zero-field splittings, magnetic moments, magnetic susceptibilities, and g values for the complex. The calculated temperature dependence of the susceptibility is compared to the reported dependence for Co(II)(acac)2(H2O)2,Co(II)(acac)2(H2O)2, yielding bounds on the strength of the tetragonal component of the crystal field. The calculated anisotropy in the susceptibility is used in an analysis of our observed pseudocontact NMR shifts for methyl and methine protons in the complex. A procedure is outlined for using a crystal field analysis to compute pseudocontact contributions to proton chemical shifts starting from g values extracted from ESR spectra. The relationship between molecular structure and crystal-field splittings is also explored via a series of ab initio electronic structure calculations for the M(II)(acac)2(H2O)2M(II)(acac)2(H2O)2 complexes with M=Mn,M=Mn, Co, Ni, and Zn. © 1999 American Institute of Physics.