Abstract
The ESR spectra of Cu(sal)2 . 4H2O, Cu(sal)2(2-pycar)2 and Cu(sal)2(3-pycar)2 (sal = salicylate ion; pycar = pyridinemethanol) at 77 K were studied. The spin Hamiltonian parameters indicate that the unpaired electron is in the antibonding-psi-blg molecular orbital. The ESR spectra of pentacoordinated Cu(II) complexes of the [Cu(phen)2X]ClO4 (phen = 1,10-phenantroline; X = Cl, Br) exhibit axial symmetry. The compressed trigonal-bipyramidal (TBP) configuration with D3h symmetry points (\z2 > ground electronic state) is consistent with the spin Hamiltonian parameters of the ESR spectra. The ESR spectra of the pentacoordinated complex of [Co(1,3-diaminopropane)3] [CuCl5].3H2O have been studied in the temperature range 100-290 K. At higher temperature (T > 160 K) the ESR spectra change their symmetry into the orthorhombic one, the square pyramidal (SP) structure of [CuCl5]3- polyhedrons is violated and a dynamical transition between the SP and TBP structures takes place.