EPR studies on Cu(3-amino, 5-methyl isoxazole)4 (ClO4)2 and Cu(3-amino, 5-methyl isoxazole)4 (NO3)2

Abstract

EPR studies have been carried out on Cu(3-AMI)₄(ClO₄)₂ and Cu(3-AMI)₄(NO₃)₂[3-AMI = 3-amino, 5-methyl isoxazole] in polycrystalline and solution forms both at room (300 K) and liquid nitrogen temperature to obtain stereochemical information and the nature of the metal-ligand bond. Cu(II) hyperfine lines are obtained in these complexes even at room temperature, which is rare for a non-dilute Cu(II) complex. No ligand hyperfine (LHF) structure from bonded nitrogen is obtained in polycrystalline samples of these complexes at the above temperatures to allow the σ-bond strength to be estimated more accurately. The change in the spectral parameters and resolution at liquid nitrogen temperature (LNT) is negligible. The above parameters obtained in MeCN and pyridine solutions of Cu(3-AMI)₄(ClO₄)₂ obtained at LNT are of comparable magnitude with the polycrystalline values indicating less solvation in these solvents. LHF structure from bonded nitrogens observed on the perpendicular component of the above sample in forzen pyridine solution enabled us to calculate the σ-bond strength more accurately than the other cases. The species formed in the DMF (N, N′-dimethylformamide) solution of Cu(3-AMI)₄(NO₃)₂ is characteristic of a CuO₆ chromophore indicating stronger solvation in the above solution. The 4s-character in the ground state of Cu(II) in all the above cases was calculated to determine the relative strengths of axial fields.