MULTIFREQUENCY SINGLE-CRYSTAL AND POWDER ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY OF [CU-2(CHP)(4)] (CHP EQUALS 6-CHLORO-2-PYRIDONATE)

Powder and single-crystal X- and Q-band EPR spectra show evidence for both intra- and inter-dimer exchange in [Cu-2(chp)(4)] (chp = 6-chloro -2-pyridonate). The antiferromagnetic intradimer exchange gives rise t o a singlet ground state and a thermally accessible S = 1 excited stat e which is described by the spin-Hamiltonian parameters (from single-c rystal measurements at 120 K) g(zz) = 2.30, g(xx) = 2.07, g(yy) = 2.05 , \D\ = 0.275 cm(-1) and \lambda\ (= \E/D\) = 0.01. D-zz and g(zz) are colinear with the Cu-Cu vector. Interdimer exchange between neighbour ing triplet state molecules is apparent by both a highly temperature d ependent linewidth and an 'extra' feature at g(eff) approximate to 2.1 , the intensity of which rapidly falls with decrease in temperature. A nalysis of the linewidth variation with temperature from single-crysta l measurements at X-band leads to an interdimer exchange parameter of J' approximate to 0.15 cm(-1). The extra feature arises from averaging of the S = 1 signals of individual dimers under the action of interdi mer exchange and occurs over only a narrow range of orientations in th e single crystal.