Anion and symmetry effects on the ESR spectra of copper complexes, part I

Abstract

Electron spin resonance (ESR) studies have been made on six substituted imidazole—copper(II) complexes in polycrystalline forms and in frozen dimethylformamide at 77 K. The complexes of N-ethylimidazole and N-propylimidazole with Cu(ClO 4) 2 show the resolution of the copper hyperfine structure. The spectral parameters are characteristic of square planar CuN 4 units with non-bonding ClO − 4 anions. Their complexes with CuCl 2 are characterized by ESR spectra indicating the presence of exchange interaction in contrast to the Cu(ClO 4) 2 complexes. In frozen dimethylformamide at 77 K they have larger g-values and smaller A-values. Also the room temperature spectrum in dimethylformamide shows only a single broad line. These features have been attributed to the low point symmetry at the Cu 2+ ion site, viz., tetrahedral with a CuN 2Cl 2 chromophore. The complexes with the thiocyanate anion, SCN −, are again found to possess a planar structure involving the anion bonding with the cation. However, no hyperfine structure could be resolved either at 295 or at 77 K. The spectra recorded in dimethylformamide at 77 K show spectra similar to those for the Cu(ClO 4) 2 complexes. ESR and optical data are combined to evaluate the bonding parameters.