COORDINATION GEOMETRIES AND COOPERATIVE ORDERING EFFECTS IN COPPER(II) COMPLEXES WITH TRIDENTATE SCHIFF-BASE DIANIONS .5. EPR-SPECTRA OF [N-SALICYLIDENE-(R,S)-ALANINATO]COPPER(II) COMPLEXES WITH DERIVATIVES OFIMIDAZOLE AND PYRAZOLE AND STRUCTURE OF IMIDAZOLE[N-SALICYLIDENE-(R,S)-VALINATO]COPPER(II)

imidazole[N-salicylidene-(R,S)-valinato]copper(II) shows square-planar coordination around the Cu2+ ion, coordinated in the basal plane by O ,N,O atoms from the tridentate Schiff base dianion and by N from the c oordinated 1-methylimidazole. In the crystal structure, enantiomers re lated by an inversion centre are bound by H bonds to units with a Cu . .. Cu distance of 8.039 Angstrom. Intermolecular H bonds stabilize sta cking of such units, which are propagated along the [010] axis. Two su ch chain systems in the unit cell are related by a glide plane paralle l to (010). The basal planes of two magnetically non-equivalent comple xes are canted by an angle of 74.64 degrees. The shortest Cu ... Cu di stance between non-parallel-aligned coordination polyhedra is 10.518 A ngstrom. On the other hand, the closest Cu ... Cu spacing of parallel- orientated coordination polyhedra is 5.628 Angstrom. Hence, in the e.p .r. powder spectrum only the coupling between ferrodistortively ordere d coordination polyhedra is manifested. E.p.r. and ligand field spectr a of a series of [N-salicylidene-(R,S)-alaninato]copper(II) complexes with imidazole, pyrazole and some of their derivatives provide evidenc e for coordination geometries ranging from square-pyramidal, with vari ous strengths of axial interaction, to square-planar. The cooperative ordering phenomena in the structure are discussed on the basis of the e.p.r. powder spectra. When the e.p.r. spectra yield crystal g values from two coupled molecular g tensors of orthorhombic symmetry, a simpl e model based on consistency of G parameters was developed for evaluat ion of the canting angle 2 gamma between aligned coordination polyhedr a and molecular g values, respectively. The data obtained from the e.p .r. powder measurements are in excellent agreement with the results of single X-ray structural studies.