The crystal and molecular structures of the ligand (E)-Pyridine-2-carbaldehyde Pyridin-2'-ylhydrazone and the palladium(II) complex Chloro[(E)-pyridine-2-carbaldehyde pyridin-2'-ylhydrazonato]palladium(II) which involves the coordination of the ligand in its anionic form

Abstract

The crystal and molecular structures of the ligand (E)-pyridine-2-carbaldehyde pyridin-2'-ylhydrazone hydrate and its complex chloro[(E)-pyridine-2-carbaldehyde pyridin-2'-ylhydrazonato]palladium(II) have been determined by single-crystal three-dimensional X-ray diffraction techniques. Crystals of the ligand are monoclinic with space group P 2₁/c. The unit cell, which contains four molecules of ligand together with approximately ten disordered water molecules, has the dimensions a 17.762(4), b 3,8717(11), c 18.503(4) Ǻ and β 107.99(2)°. Crystals of the complex are triclinic with space group P1, and the unit cell has the dimensions a 6.9721(3), b 9.0739(11), c 9.1304(9) Ǻ, α81.116(9), β 88.778(8) and γ 81.392(8)°; Z = 2. The ligand structure was solved by direct methods and refined with anisotropic thermal parameters for all non-hydrogen atoms and isotropic thermal parameters for hydrogen and solvent atoms. The complex structure was solved by conventional Fourier methods and refined with anisotropic thermal parameters for all non-hydrogen atoms. A full-matrix least-squares method was employed for both structures based on 1295 and 2224 statistically significant reflections giving final values of R 0.061, R_w 0.068 and R 0.028, R_w 0.030 for the ligand and complex respectively.

The structure analysis of the ligand shows definite evidence of delocalization of lone pair electrons in the hydrazine moiety. The ligand in its anionic form coordinates in a tridentate manner to the palladium atom in the complex through the two pyridine nitrogen atoms and the distal nitrogen of the hydrazine residue. A square-planar array is formed by a chlorine atom occupying the fourth position. Molecular dimensions suggest that the lone pair on the proximal nitrogen is delocalized over the entire molecule. Standard valence-bond and 'increased valence' methods have been applied in order to determine resonance schemes consistent with the observed structures of both the ligand and its complex.