Synthesis and structural characterisation 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'-pyridylhydrazone (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 characterised 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 atom coordinating to the imino nitrogen and one of the pyridyl nitrogen atoms (Cu-N, 2.070(7), 2.117(5) Angstrom). The second pyridyl nitrogen is involved in an intramolecular hydrogen bond with the hydrogen atom of the hydrazono moiety. The related isomer [Cu(PPh(3))(2)(E-papyH)] ClO4 crystallises with two non-equivalent molecules within the asymmetric unit. The first has a distorted tetrahedral geometry with regular copper-nitrogen distances (Cu-N, 2.141 (4), 2.130(6) Angstrom, whereas in the second the copper atom is five-coordinate with a distorted trigonal bipyramidal stereochemistry and exhibits long axial copper-nitrogen 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 there is no isomerisation about the imino carbon-nitrogen bond and that the five-coordinate nature of the complex is retained.