SYMMETRY EFFECTS IN THE EPR-SPECTRUM OF BIS(NITROACETONATO)BIS(PYRIDINE)CU(II)

The low-temperature EPR spectrum of bis(nitroacetonato)bis(pyridine)Cu(II), diluted in a single crystal of the isomorphous Zn(H) analog, is reported. The g tensor, the metal hyperfine and quadrupole coupling tensors, and the nitrogen hyperfine tensor have been obtained. Additional hyperfine lines have been detected along some orientations and attributed to the coupling of the unpaired electron with the two out-of-plane hydrogen atoms of the chelate rings. The principal values and orientations of the experimental tensors differ considerably from those of the closely related bis(ω-nitroacetophenonato)- bis(4-methylpyridine)Cu(II). The relevance of lattice effects on the symmetry of the two compounds, and hence on the properties of their magnetic parameters, is discussed. The description of the overall electronic structure appears to be complicated by the fact that different effective symmetries" are reflected by different spin-Hamiltonian parameters. © 1978."