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 dimeric (trichloroacetato)copper(II) complexes, of which magneto-structural data are available: The larger is the distortion of the coordination geometry from square pyramidal (SP) toward trigonal bipyramidal (TBP), the longer is the Cu···Cu distance in the dimers. The elongation of the Cu···Cu distance is accompanied by a reduction of the zero-field splitting parameter (D), the anisotropic exchange parameter (D(ex)), and the peak separation of the two peaks in the electronic spectra (Δv̄(max)). The splitting of the carboxylato stretching frequencies, Δv̄ (=v̄ - v̄(sym)), increases with the distortion. Good linear correlations have been observed between the values of these parameters and the Cu···Cu distances. The axial ESR spectra with g(is parallel with) > g(is perpendicular to) and the electronic spectra suggest that the ground state of the Cu atom is essentially d(x²- y²), even in the metal geometry of the greatest distortion toward TBP (the z-axis is along the longest Cu-O bond).