EXTENDED HUCKEL CALCULATIONS IN SPECTRAL AND MAGNETIC STUDIES OF 2 DISTORTION ISOMERS OF BIS(1,3-DIAMINOBUTANE)COPPER(II) PERCHLORATE

Two isomeric forms of bis(1,3-diaminobutane)copper(II) perchlorate wer e separated by recrystallisation. The spectral and electronic properti es of the blue-violet and red-violet isomers were investigated. The pe rchlorate anion is coordinated more strongly in the blue-violet isomer , which is seen in the IR and electronic spectra and the oxygen atom c ontribution to the axial MO. Extended Huckel calculations show that te tragonality has an effect on the effective charge on the central coppe r(II) ion, but not on the amount of d-s mixing. The isomers obey the C urie-Weiss law in the temperature range 70-310 K with C = 0.388(6) and Theta = 6(1) for the blue-violet isomer and C = 0.365(5) and Theta = 7(1) for the red-violet isomer. The Curie constants accord with the di fferences in the ligand field.