Anomalous Magnetic Properties of Certain First Series Transition-Metal Complexes Studied by Magnetochemical and Spectroscopic Methods.

Abstract

Magnetic studies, Mossbauer spectra and the results of extensive tests on the relevance of theoretical models to certain anomalous magnetic properties of Ti(III), Ni(II), Fe(II), and, Fe(III) complexes are reported. An extensive discussion of exchange interactions is given. Models for exchange coupled d1 or d5 ions with a 2T2 ground state are examined and applied with some success to 29 Ti(III)-Ti(III) and Fe(III)-Fe(III) complexes. For the d1 – d1 system, the effect of the excited 2E state on the magnetic susceptibilities is considered. The susceptibilities are found to be uniformly raised by a relatively small amount, over the temperature range 25°K to 400°K. A number of theoretical models for Fe(II) or Fe(III) systems, which assume either a single species or two species crossover are discussed. Spin-orbit and configurational mixing effects are examined. Second order perturbation and more accurate methods for the allowance of such effects are compared. A simple two level model is used to reproduce the available magnetic data for 27 ferrous crossover complexes. A simple means of reproducing the results of a full configuration interaction calculation on the d6 system is given. Mossbauer studies on certain ferrous complexes which appear to display a triplet ground state are reported. Anomalous magnetic data for some quadridentate Schiff base ligated Ni(II) complexes are reported. Discrete polymeric structures are suggested, to explain the anomalous results.