Triplet-state E.P.R. studies of exchange coupled copper(II) and silver(II) pairs in zinc(II) bis[N.N.-diisopropyldithiocarbamate]

Abstract

Ambient temperature single crystal triplet-state E.P.R. studies on exchange coupled Cu²⁺-Cu²⁺ pairs in zinc(II) bis[N,N-diisopropyldithiocarbamate] matrix and temperature dependent E.P.R. studies on powder samples of Cu²⁺-Cu²⁺ and Ag²⁺-Ag²⁺ pairs, separated by a distance of 3·545 Å, in the same host lattice are reported. In addition to the doublet spectra, we observed the triplet lines arising due to spin-spin interactions. The directions of g and D-tensors in Cu²⁺-Cu²⁺ pairs vary by 42° in the xz-plane. The D-tensor seems to receive its contribution both from the dipolar and pseudo-dipolar interactions. The zero-field splitting (Z.F.S.) tensor, ‘D’, increases linearly with decrease in temperature down to 80K. This effect is seen in both Cu²⁺-Cu²⁺ and Ag²⁺-Ag²⁺ pairs: it is tentatively attributed to a crystal contraction at low temperatures. The integrated intensities of ΔM s = ±2 E.P.R. transitions of the triplets have been used to estimate the magnitude and sign of isotropic exchange coupling constants (2J). The values of 2J for Cu²⁺-Cu²⁺ and Ag²⁺-Ag²⁺ pairs are found to be 40·2 cm^-1 and 62·5 cm^-1, respectively. The interaction in both the systems has been found to be ‘ferromagnetic’.