Ligand arrangement in tetragonally distorted CuO4N and CuO4N2 chromophores formed from copper(II)α-nitroketonates and sterically hindered N-bases

Abstract

The 1 : 1 and 1 : 2 adducts of copper(II)-α-nitroketonates (CuL₂) with sterically hindered nitrogen bases (B)(L =α-nitroketonato-anion from nitroacetone, 2-nitroacetophenone, 3,3-dimethyl-1-nitrobutan-2-one, or 3-nitrocamphor; B = 2-methyl- or 2,6-dimethyl-pyridine or quinuclidine) have been studied as solids and in solution. An investigation has been carried out on the symmetry and ligand arrangement about Cu^II of complexes of formula CuL₂B (CuO₄N chromophore), including those with B = pyridine or 4-methylpyridine. On the basis of room temperature electronic spectra and low temperature (110 K) e.s.r. spectra, all complexes are assigned an approximately square pyramidal structure in solution, most with the nitrogen atom co-ordinated in the basal plane of the pyramid (along the d_x²–y² or d_xy. orbitals) and one oxygen atom of an α-nitroketonato-group occupying the apical position. In many cases the position of the nitrogen atom in the corresponding solid complexes, whether basal or apical, could not be established with certainty owing to the lack of pertinent e.s.r. data. For complexes of formula CuL₂B₂(B = 2-methyl- or 2,6-dimethyl-pyridine) electronic and e.s.r. spectral data indicate tetragonally elongated structures with both nitrogen atoms co-ordinated in the equatorial plane (along the d_x²–y² or d_xy orbitals).