EPR spectra of triplet states with large zero-field splitting. [Cu(bipy)OH)]2SO4·4H2O

The polycrystalline powder and single-crystal EPR spectra of [Cu(bipy)(OH)]2SO4· 4H2O were recorded in the range of temperatures at both X- and Q-band frequencies. The polycrystalline powder spectra were used to estimate that the zero-field splitting in this complex must be fairly large, > 1 cm−1. The single-crystal spectra recorded in four different planes were analyzed through a diagonalization of the full Hamiltonian matrix, allowing for nonparallel g and D tensors. The difficulties which arise for the interpretation of the spectra were discussed. The values of g and D were found to have coincident z axes, with the x and y axes rotated by approximately 45°. The data obtained from the analysis of the single-crystal spectra were used to calculate the polycrystalline powder spectra, with satisfactory agreement with experiment.