Ligand arrangement and tetragonal distortion in CuO4N2 chromophores studied by electronic and electron spin resonance spectroscopy

Abstract

A series of nitrogen-base adducts of copper(II)α-nitroketonates of general formula [CuL₂B₂](L =α-nitroketonato anion, B = pyridine or 4-methylpyridine; chromophore CuO₄N₂) have been prepared and their structures investigated by magnetic, spectroscopic, and X-ray measurements. Room-temperature solid state and solution electronic spectra and low temperature (110 K) e.s.r. spectra, on both polycrystalline samples diluted in their isomorphous or non-isomorphous zinc(II) matrices and frozen solutions in CHCl₃–CH₂Cl₂(1 : 1), indicate that the Cu^II ion is in a site of elongated tetragonal symmetry with ‘restricted’ distortion caused by in-plane co-ordination of the nitrogen atoms and in-plane–out-of-plane co-ordination of the bidentate O-donors. The analogous bis-adducts with pyridine and 4-methylpyridine of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)copper(II) have also been examined and structures assigned both in the solid state and in solution. For some of the above species the polycrystalline samples give e.s.r. spectra indicative of the presence of additional magnetic centres with compressed tetragonal symmetry.