A short hydrogen bonded columnar structure: Synthesis, spectroscopic studies and x-ray structure of a palladium(ii) complex of alfa-furil dioxime

Synthesis, spectroscopic studies and single crystal X-ray structure of [Pd(Hafdo)2], where H2afdo is a-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-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 a-amine oximes are reported. Efforts are made to correlate the O—O separation in these complexes with the infrared absorptions and with the values of 1H nmr chemical shifts of the bridging proton.