Tetragonal distortions in the jahn-teller active copper pyridine-N-oxide complexes

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Abstract
The Jahn-Teller (JT) and the E.P.R. parameters of the trigonal, JT-active hexakispyridine-N-oxide complex Cu(C5H5NO)6 2- are calculated from the results of extended Hückel molecular orbital calculations on a series of distorted geometries of this complex. These geometries are obtained from a recent, low temperature, neutron diffraction study and compared with a monoclinic, static, modification of the corresponding nitrate complex. For two different distortion models, the JT minimum is obtained for a tetragonally elongated octahedron. The JT parameters are in very reasonable agreement with the experimental ones. The EPR parameters are compared with newly determined experimental values obtained by a re-evaluation, using matrix diagonalization instead of a perturbation treatment, of earlier measurements on Cu(C5H5NO)6(BF4)2 at 4·2 K and on Cu(C5H5NO)5DMF(ClO4 2 at room temperature. On the basis of these computations, the E.P.R. parameters, and especially the very small isotropic copper hyperfine coupling, can be understood.

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