Coordination chemistry of mixed pyridine-phenol ligands; mononuclear palladium(II) and dinuclear copper(II) complexes of derivatives of bidentate N, O-chelating ligands based on 2-(2-hydroxyphenyl)pyridine

Abstract

The new ligands 2-(2-hydroxyphenyl)-4- tbutyl-pyridine (HL 1), 2-(2-hydroxyphenyl)-6-methylpyridine (HL 2) and 2-(2-hydroxyphenyl)-6-[(2-phenyl)ethyl]pyridine (HL 3) were prepared. They are all substituted derivatives of the simple N, O-bidentate chelating ligand 2-(2-hydroxyphenyl)pyridine. HL 1 is solubilised derivative bearing a tBu substituent in a position which will not sterically interfere with metal-ion coordination; HL 2 and HL 3 contain substituents at C 6 of the pyridyl ring, adjacent to the N atom, which will therefore sterically hinder metal-ion coordination. The complexes [PdL 2] (PdL 2] (L = L 1, L 2 and L 3) were prepared and structurally characterised to determine the effects (if any) of the substituents on the structures of the metal complexes. All are four-coordinate complexes with square planar coordination geometry about the Pd(II) ion, but the sterically hindered ligands L 2 and L 3 have to adopt a different conformation from L 1 to allow planar coordination, resulting in “bowl-like” structures. [Cu 2(L 1) 4] was also prepared and found to be a phenolate-bridged dinuclear complex in the solid state, both by X-ray crystallography and EPR measurements. In solution, however, it dissociates to give [Cu(L 1) 2] monomeric units. Cu(II) complexes of L 2 and L 3 could not be isolated.