Metal complexes containing the monoanion, dianion and the neutral form of the ligand N-(2-carboxylphenyl)pyridine-2′-carboxamide

Abstract

New complexes of the formulae M(LH) 2· nH 2O (M = Co, Ni, Cu, Zn; n = 2, 2.5, 3), Cu 2(LH) 2L· 3H 2O, PdL·H 2O, Pt 3(LH) 4L·7H 2O, M 2(LH) 2(OH) 2· nH 2O (M = Co, Ni, Zn; n = 2, 4), CuL, M(LH 2) 2Cl 2· EtOH (M = Co, Cu; EtOH = ethanol), Ni(LH 2) 2Cl 2· EtOH·H2O, M(LH 2) 2X 2 (M = Co, Ni; X = NCS, ONO 2), Zn(LH 2) 2(NO 3) 2, Zn(LH 2)(LH)Cl, Cu(LH 2)- (LH)NO 3 and Cu 3(LH) 3L(NO 3), where LH 2= N-(2- carboxylphenyl)pyridine-2′-carboxamide, have been isolated. The complexes were characterised by elemental analyses, conductivity measurements, magnetic moments and spectral (IR, 1H NMR and electronic) studies. Varying stereochemistry is assigned for the complexes prepared in the solid state. The complexes M(LH) 2· nH 2O (M = Co, Ni, Cu, Zn), Cu 2- (LH) 2L·3H 2O and Cu 3(LH) 3L(NO 3) appear to be polymeric, while dimeric structural types are assigned for M 2(LH) 2(OH) 2· nH 2O (M = Co, Ni, Zn) and CuL. Only palladium(II) at acidic pH and copper(II) at basic pH promote amide deprotonation on coordination and yield doubly deprotonated complexes. Coordination of the neutral carboxylic group is not observed for the complexes of LH 2; the carboxylate ion exhibits monodentate coordination in the compounds of LH - and L 2-. The neutral amide group of the ligands LH 2 and LH − is coordinated to the metal ions through oxygen, while N(amide)-coordination is observed for the L 2- complexes. The secondary amide bond shows the rare iminol type of coordination in Cu(LH) 2·2H 2O.