Electron spin resonance and electronic spectral investigation on square planar copper(II) complexes ofN-ethyl- andN-propylimidazole

Summary Electron spin resonance studies have been carried out onN-ethylimidazole andN-propylimidazole 4 : 1 complexes of CuX₂ salts (X = ClO₄^–, NO₃^–, , Br^– or Cl^–) in their polycrystalline and undiluted form at 295 K and 77 K. Cupric ion hyperfine structural resolution is observed for all the complexes at 295 K and the spectra are characteristic of a CuN₄ chromophore with axial symmetry. In complexes involving ClO , Br^– and Cl^– the anions are nonbonding, whereas those with the NO₃^– anion are weakly bonding. The electronic and e.s.r. spectral data have been correlated. The resolution of Cu²⁺ ion hyperfine structure in these complexes is attributed to a decrease in the dipolar interaction and has been observed for the first time since the first resolution reported in 1954 for CuN₄ coordination with square planar symmetry for ,,,-tetraphenylporphyrincopper (CuTPP).