Structural features of palladium(II) complexes with α-hydroxycarboxylate and aromatic α,α′-diimine ligands

The neutral α-hydroxycarboxylate complexes [Pd(bpy)(GLYO)]·3H2O (1), [Pd(bpy)(MANO)]·4H2O (2) and [Pd(GLYO)(phen)]·5H2O (3), together with the palladium(II) complexes [Pd(phen)2](NO3)2 (4) and [Pd(CH2COCH3)(bpy)(Cl)] (5) (where GLYO and MANO are the glycolate and mandelate dianions, respectively, and bpy and phen, 2,2′-bipyridine and 1,10-phenantrholine, respectively), have been prepared by reaction of [Pd(bpy)Cl2] or [PdI2(phen)] with salts of α-hydroxycarboxylic acids in water. These compounds were characterized by elemental analysis, mass spectrometry, 1H and 13C NMR, UV–Vis, IR spectroscopy, TG analysis and single crystal X-ray diffraction. The aforementioned studies confirmed the formation of a variety of square-planar mononuclear compounds (1–3) where the α,α′-diimine ligands exhibit a rather simple bidentate chelating role and the α-hydroxycarboxylate ligands are dianionic. A variety of ligand distortions, hydrogen-bonding and stacking interactions were found and these were thoroughly analyzed. In compounds 1 and 3, the complex molecules are stacked in such a way that the coordination planes are parallel to one another. The Pd⋯Pd distances between the nearest stacked neighbors are 3.8043(6) and 3.302(2)/3.475(1) Å, respectively. Compounds 1–3 have been tested in vitro for cytotoxicity on HeLa-299 human tumor cell lines.

A variety of ligand distortions, hydrogen-bonding and stacking interactions that govern the supramolecular structure were found and analyzed in the neutral square-planar α-hydroxycarboxylate complexes [Pd(bpy)(GLYO)]·3H2O (1), [Pd(bpy)(MANO)]·4H2O (2) and [Pd(GLYO)(phen)]·5H2O (3) in the solid state. Spectroscopic and thermal stability data are reported for the complexes 1–3.Figure optionsDownload as PowerPoint slide