Coordination geometries and cooperative ordering effects in copper(II) complexes with tridentate Schiff base dianions—VI Structure and EPR spectra of (imidazole) (N-salicylidene-beta-alaninato)copper(II)

The crystal and molecular structure of (imidazole) (N-salicylidene-beta-alaninato)copper(III), monoclinic, space group C/2c, was solved by a single crystal X-ray structure analysis and refined to R = 0.0577 for 1286 observed reflections. The coordination polyhedron around Cu(II) is an axially elongated square-pyramid, the basal plane being formed by the (O, N, O) atoms of the tridentate Schiff base and the N atom of imidazole. The apex of-the pyramid is occupied by the terminal carboxylic atom of adjacent molecule, thereby giving rise to centrosymmetric dimers. Non-parallel aligned stacks of dimeric units are propagated in the unit cell. The powder and single-crystal EPR spectra show cooperative g factors resulting from the weak coupling between two misaligned g tensors from dimeric units ordered in a disturbed-ferrodistortive way. Since the N-N axes, corresponding to g(y), are oriented nearly parallel; the g-g coupling shifts only the values of g(z) and g(x). A complete consistency between the angular spectroscopic EPR behaviour and the X-ray structural data was found. (C) 1998 Elsevier Science Ltd. All rights reserved.