The electron spin relaxation and reorientation correlation times of 63CU(II)-bis(dimethyldithiocarbamate) in Solution

Abstract

The electron spin relaxation of 63Cu(II)-bis(dimethyldithiocarbamate) has been studied as a function of temperature in benzene, toluene, carbon disulfide, carbon tetrachloride, chloroform, and dichloromethane. In order for the fast motional spin relaxation theory to be tested the anisotropies of the spin-Hamiltonian parameters were determined from spectral simulations of the EPR in frozen toluene: these are ΔA = − 370MHz, Δg = 0.0672. With these values it is found that the spin relaxation of Cu(II)-bis(dimethyldithiocarbamate) is explained by the existing fast motional relaxation theories. The reorientational correlation time (τ 2) and spin-rotational term (α″) have been determined as functions of temperature and solvent. It has been found that (a) for a given solvent the linear relationship τ 2 = (V effη KT) + τ 0 is obeyed, and (b) for various solvents the linear relationship τ 2 = C η + ε′ 0 is obeyed; these results support previous findings that the reorientational correlation time of a molecule such as the one studied can be treated using modified hydrodynamic theories. We have also found that the linear plots of τ 2 vs (η/T) for different solvents intersect at a common “isorotational point.” This behavior implies a linear correlation between V eff and τ 0, and is also found in the data of Kivelson and Huang. These results support Kivelson's formulation of V eff in terms of the stickiness factor, provided that this increases with temperature. Finally the α″ measured is found to conform to simple theories of spin-rotational coupling and is consistent with isotropic rotational diffusion.