The coordination chemistry of N-(2-pyridyl)pyridine-2′-carboxamide; A potentially tridentate ligand containing one secondary amide and two 2-pyridyl donor groups

Abstract

New complexes of the general compositions M(LH)X 2 (M = Co, Zn; X = Cl, Br, I), Zn(LH)(NCS) 2, Zn(LH)(NO 3) 2 ·H 2O, Cu(LH)X 2 (X = Cl, Br, ONO 2), Ni(LH)Cl 2·H 2O, Co(LH) 2X 2 (X = NCS, ONO 2), Ni(LH) 2X 2 (X = Cl, Br, NCS, ONO 2), Pt(LH) 2Cl 2 and MLCl· nH 2O (M = Ni, Cu, Pd; n = 2, 3), where LH = N-(2-pyridyl)pyridine-2′-carboxamide, have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods, magnetic susceptibilities and spectroscopic (IR, ligand field, 1H NMR) studies. Pseudotetrahedral, square planar, square pyramidal and distorted octahedral stereochemistries are tentatively assigned in the solid state. Most complexes appear to be monomeric, while polymeric structural types are attributed for Ni(LH)Cl 2·H 2O and CuLCl·2H 2O. The neutral amide group of LH is coordinated to Co(II), Ni(II), Cu(II) and Zn(II) through oxygen, while N-coordination is observed for PdLCl·2H 2O. The amide group of L − is bound to different Cu(II) atoms in CuLCl·2H 2O through both its nitrogen and oxygen. The rare O-coordination of the deprotonated amide bound is proposed for NiLCl· 3H 2O. The N(1) atom is not involved in coordination except in the complexes Ni(LH)Cl 2·H 2O, NiLCl· 3H 2O and CuLCl·2H 2O, where both pyridine residues are coordinated. The variation in structural types observed is believed to be a consequence of the stereochemical adaptability of the ligand to the electronic demands of the metal ions.