Copper(II)-activated transformation of azomethine to imidate: Synthetic and structural studies

Abstract

The Schiff base 2-pyridine-carboxaldehyde 4-dimethylaminobenzoylhydrazone (HL, 1) was prepared by reacting 2-pyridinecarboxaldehyde and 4-dimethylaminobenzoylhydrazine in a 1:1 molar ratio in methanol. Reaction of HL (1) with Cu(O2CCH3)2·H2O (in a 1:1 molar ratio) in methanol afforded a dinuclear copper(II) complex, [Cu2(μ-O2CCH3)2 L2′]·2H2O (2). The azomethine functionality (-CH=N-) of 1 is converted to imidate (-C(OMe)=N-) in the complexed ligand I′-. Molecular structures of both 1 and 2 were determined by X-ray crystallographic studies. The dinuclear molecule of 2 is centrosymmetric and contains two monoatomic bridging acetate groups. Each copper(II) centre is in a square-pyramidal N2O3 coordination sphere. The ligand, L′- coordinates the metal ion via the pyridine-N, the imidate-N, and the deprotonated amide-O atoms. One of the acetate oxygen atoms completes the N2O2 square-plane. The oxygen of the symmetry-related acetate fills the apical coordination site. Structural parameters are consistent with both copper ions being in a +2 oxidation state. The room temperature magnetic moment is 1.89 μB (per Cu). In powder phase the complex displays an axial EPR spectrum at 298 K. The complex is nonconducting in methanol solution. The electronic spectrum shows a ligand field absorption at 680 nm and charge transfer bands in the range 426-215 nm. © 2000 Elsevier Science B.V.