STRUCTURE OF (PYRAZOLE-KAPPA-N-2)[(S)-N-SALICYLIDENE-KAPPA-O-ALANINATO(2 -)-KAPPA-N,KAPPA-O]COPPER(II)-PYRAZOLE (1/1)

Reaction of the parent aqua[(S)-N-salicylide-nealaninato]copper(II) dihydrate with an excess of pyrazole gives the title compound in which only one of the two pyrazole molecules is coordinated to Cu-II (the other is doubly hydrogen bonded to the complex molecule). The Cu-II coordination can be described as square pyramidal (4 + 1), the basal plane being formed by the heteroatoms of the tridentate Schiff base ligand and the N atom of the pyrazole molecule. A neighbouring chelate provides a semi-coordinating O(3) atom in the axial direction [Cu...O(3) = 2.595 (3) Angstrom], thus forming polymeric chains along the a axis in the crystal. The title complex serves as a model to study the mechanism of a racemization reaction of amino acids catalyzed by vitamin B-6 (or salicylaldehyde) and metal ions. The results, combined with those obtained previously for potassium isocyanato[(R,S)-N-salicylidene-alaninato]cuprate(II) do not support the general mechanism proposed earlier for the racemization reaction but instead suggest an active role for the nucleophilic solvent in the catalytic reaction.