A SHORT HYDROGEN BONDED COLUMNAR STRUCTURE: SYNTHESIS, SPECTROSCOPIC STUDIES AND X-RAY STRUCTURE OF A PALLADIUM(II) COMPLEX OF ALFA-FURIL DIOXIME

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Abstract
Synthesis, spectroscopic studies and single crystal X-ray structure of [Pd(Hafdo)2], where H2afdo is α-furilglyoxime, were carried out because of its potential columnar stack structure and the existence of a short intramolecular hydrogen bond. The compound crystallizes in the orthorhombic space group Pnab with a=6.930(3), b=14.286(2) and c=19.837(4) Å. The intensity data were collected on a CAD-4 diffractometer and the structure was refined to a final R value of 6.1%. The central metal atom in this inner complex has planar geometry and the oxime oxygen atoms are involved in a short intramolecular hydrogen bond with O[sbnd]O distance of 2.583(4) Å. The complex molecules are stacked above one another along the crystallographic a axis with adjacent molecules rotated 90° with respect to each other. The Pd-Pd distance is 3.465(4) Å. The two oxygen atoms of the planar furane groups are separated by 2.686(4) Å and the furane rings are oriented at an angle of 46.7° with respect to each other. The columnar stack structure in this compound is similar to chelate structures exhibiting one-dimenisonal electrical conduction properties. The infrared spectra and the chemical shifts of the bridged proton of the title compound and several other metal complexes of α-amine oximes are reported. Efforts are made to correlate the O[sbnd]O separation in these complexes with the infrared absorptions and with the values of 1H nmr chemical shifts of the bridging proton.