ESR Investigation of Some o-Phenylenebis(dimethylarsine) Complexes of Cobalt and Nickel

The ESR spectra have been obtained for six complexes with the general formulas [Ni(diars)₂X₂] X and [Co(diars)₂X₂]⁰, where X is Cl, Br, and NCS and diars is o‐phenylenebis(dimethylarsine), using pure polycrystalline solids and, in the case of the nickel complexes, solutions, and frozen solutions. Ligand hyperfine interactions with ⁷⁵As, ^35,37Cl, ^79,81Br, and ¹⁴N have been observed and discussed. The data suggest that a model based on $d^7$ Ni(III) with a ${}^2{A}_g$ ground state may be adequate for these complexes.