CHARACTERIZATION OF DIMERIC COPPER(II) TRICHLOROACETATE COMPLEXES BY ELECTRON-SPIN-RESONANCE, INFRARED, AND ELECTRONIC REFLECTANCE SPECTRA - CORRELATION OF SPECTRAL PARAMETERS WITH MOLECULAR-GEOMETRY

ESR, IR, and electronic reflectance spectral data are presented for di meric (trichloroacetato)copper(II) complexes, of which magneto-structu ral data are available: The larger is the distortion of the coordinati on geometry from square pyramidal (SP) toward trigonal bipyramidal (TB P), the longer is the Cu...Cu distance in the dimers. The elongation o f the Cu...Cu distance is accompanied by a reduction of the zero-field splitting parameter (D), the anisotropic exchange parameter (D-ex), a nd the peak separation of the two peaks in the electronic spectra (Del ta (v) over bar(max)). The splitting of the carboxylato stretching fre quencies, Delta (v) over bar(= ($) over bar(asym) - ($) over bar(sym)) , increases with the distortion. Good linear correlations have been ob served between the values of these parameters and the Cu Cu distances. The axial ESR spectra with g parallel to > g perpendicular to and the electronic spectra suggest that the ground state of the Cu atom is es sentially d(x2-y2), even in the metal geometry of the greatest distort ion toward TBP (the z-axis is along the longest Cu-O bond).