STRUCTURAL AND DYNAMIC ASPECTS OF THE PARAMAGNETIC CU(II)METHYLPYRAZOLE COMPLEXES

The Cu(II)methylpyrazole complexes Cu(3-MP)4SO4, Cu(3-MP)4Cl2 and Cu(3 -MP)2ac2 were examined by ESR spectroscopy. The ESR parameters were de termined by complete simulation of the solution and powder spectra. Th e pattern of the ESR spectra of Cu(II) complexes with N-donor ligands in solution is mainly determined by the ratio of the anisotropies of t he coupling tensors g and A and the line widths DELTAB(i) = f(m(I)) fo r the individual hyperfine transitions. The values of the coupling ten sors and the dynamic properties (reorientation times) of the complexes depend in a characteristic manner on the nature and geometric paramet ers of the N-donor ligands. The existence of the Cu(II)methylpyrazole complexes in solution was proven by the analysis of the N-14-shfs (sup er hyperfine structure) which indicates the coordination of four molec ules of 3-methylpyrazole. The pattern of the powder spectra reflect th e pronounced influence of the anions. The largest effect was observed for the Cu(3-MP)2ac2 Complex. The acetate anion acts as a bridging lig and and leads to the formation of a dimer with D = 0.077 cm-1 and a Cu 2+ ... Cu2+ distance of 347 pm, which is remarkably larger than in Cu( ac)2 . H2O.