EPR of two Cu2+ complexes showing dynamic Jahn-Teller effects

Abstract

The powder electron paramagnetic resonance spectra of ∼1% Cu doped into [Zn(bipy)2(NO2)]NO3 and [Zn(bipyam)2(NO2)]NO3, bipy = 2,2′-bipyridyl, bipyam = 2,2′-bipyridylamine, over the temperature range 4.2–300 K are reported. For [Zn/Cu(bipy)2(NO2)]NO3 a spectrum characteristic of a tetragonally elongated octahedral complex with a slight orthorhombic distortion is observed below ∼50 K, but above this temperature the signals associated with the two higherg-values gradually converge. At low temperature a spectrum similar to that of the bipy complex is observed for [Zn/Cu(bipyam)2(NO2)]NO3, but between 40 and 60 K the spectrum gradually changes to one characteristic of a tetragonalg-tensor with g∥ < g⊥. The spectra may be interpreted satisfactorily with a model in which the temperature dependence of theg-vainlues is estimated from the vibronic wavefunctions of a copper(II) complex under the influence of second-order Jahn-Teller coupling and a ligand field of tetragonal symmetry perturbed by crystal lattice forces. The results are consistent with the crystal structures reported for the compounds at various temperatures.