SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A PAIR OF LINKAGE ISOMERS OF COPPER(I) PYRIDINE-2-CARBALDEHYDE 2'-PYRIDYLHYDRAZONE COMPLEXES

The copper(I) linkage isomers of pyridine-2-carbaldehyde 2'-pyridylhyd razone (papyH), [Cu(PPh(3))(2)(Z-papyH)]ClO4 and [Cu(PPh(3))(2)(EpapyH )] ClO4, have been prepared by the reaction of [Cu(PPh(3))(2)(CH3CN)(2 )]ClO4 with the Z- and E-form of papyH. The complexes have been charac terised by spectroscopic methods and single crystal X-ray diffraction analysis. In the solid state [Cu(PPh(3))(2)(Z- papyH)]ClO4 consists of discrete monomers of distorted tetrahedral geometry, with the metal a tom coordinating to the imino nitrogen and one of the pyridyl nitrogen atoms (Cu-N, 2.070(7), 2.117(5) Angstrom). The second pyridyl nitroge n is involved in an intramolecular hydrogen bond with the hydrogen ato m of the hydrazono moiety. The related isomer [Cu(PPh(3))(2)(E-papyH)] ClO4 crystallises with two non-equivalent molecules within the asymme tric unit. The first has a distorted tetrahedral geometry with regular copper-nitrogen distances (Cu-N, 2.141 (4), 2.130(6) Angstrom, wherea s in the second the copper atom is five-coordinate with a distorted tr igonal bipyramidal stereochemistry and exhibits long axial copper-nitr ogen distances of 2.371(5) and 2.767(5) Angstrom. The H-1 and C-13(H-1 ) NMR spectra of [Cu(PPh(3))(2)(E-papyH)] ClO4 show that in solution t here is no isomerisation about the imino carbon-nitrogen bond and that the five-coordinate nature of the complex is retained.