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

Article abstract of DOI:10.1016/S0277-5387(97)00384-7

The new ligands 2-(2-hydroxyphenyl)-4-^tbutyl-pyridine (HL¹), 2-(2-hydroxyphenyl)-6-methyl-pyridine (HL²) and 2-(2-hydroxyphenyl)-6-[(2-phenyl)ethyl]pyridine (HL³) were prepared. They are all substituted derivatives of the simple N,0-bidentate chelating ligand 2-(2-hydroxyphenyl)pyridine. HL¹ is solubilised derivative bearing a ^tBu substituent in a position which will not sterically interfere with metal-ion coordination ; HL² and HL³ contain substituents at C⁶ of the pyridyl ring, adjacent to the N atom, which will therefore sterically hinder metal-ion coordination. The complexes [PdL₂] (L = L¹, L² and L³) 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 L² and L³ have to adopt a different conformation from L¹ to allow planar coordination, resulting in bowl-like structures. [Cu₂(L¹)₄] was also prepared and found to be a phenolatebridged dinuclear complex in the solid state, both by X-ray crystallography and EPR measurements. In solution, however, it dissociates to give [Cu(L¹)₂] monomeric units. Cu(II) complexes of L² and L³ could not be isolated.