Electron spin resonance study of paramagnetic ion pair systems with non-parallel alignment of their axes

Abstract

The theory of the e.s.r. of dipolar coupled dissimilar ion pairs of spin ½, appropriate to dimers, binuclear complexes and single crystal situations, is developed and applied to the computer simulation of ΔM_s=± 1 and 2 spectra due to randomly oriented dimer or binuclear complexes. Exchange coupling is not included in the perturbation theory treatment, and the reasons for this are discussed. The dissimilar ion pairs considered here consist of ion sites which are otherwise identical except that there is a non-parallel alignment of their principal axes, but the theory would apply equally well to e.g. mixed metal copper(II)–vanadyl pairs. Reinterpretation of previously reported results on the binuclear copper(II), vanadyl and titanium(III) complexes of tetrakis(aminomethyl)methane in frozen water + glycol solutions, and on the copper(II) binuclear compex of 3,6,-dioxaoctane-1,8-diamine-NNN′N′-tetra-acetic acid in aqueous solutions, has been possible in the light of this theoretical development. It is possible to assess likely conformations and symmetries of these binuclear complexes and to make a definite choice in each case except for the titanium(III) tetrakis(aminomethyl)-methane complex, where the small anisotropy in g-values and the lack of hyperfine structure made it impossible to determine any reliable symmetry information.