X-ray structural studies on some divalent 3d metal compounds of picolinic and isonicotinic acid N-oxides

Abstract

Nine structures of 3 metal complexes of picolinic and isonicotinic acid N-oxides have been solved for this study. Bis(picolinato N-oxide)diaquamanganese(II), cobalt(II) and nickel(II) form an isomorphic series, from which the corresponding copper(II) complex differs, probably due to Jahn-Teller distortion. In all four complexes the picolinic acid N-oxide coordinates to the metal ion through the N-O oxygen and one of the (COO) oxygens, forming a stable six-membered chelate ring. Isonicotinic acid N-oxide can join to the metal ions in many different ways. In trans-bis(isonicotinato N-oxid)tetraaquamanganese(II) the ligand coordinates to the central metal ion only through one of the carboxylic oxygens. Bis(isonicotinate N-oxide)hexaaquairon(II), -cobalt(II)1 and -nickel(II)1 belong to an isomorphic series where the metal ion forms an hexaaqua cation with coordinated water molecules. There is no direct coordination between metal ions and isonicotinate N-oxide and the isonicotinate N-oxide anion is present in these structures instead. In di-u3-hydroxo-µ-sulfato-tetrakis-µ-(isonicotinato N-oxide)tetraaquatetracopper(II)2 the isonicotinato N-oxide ligand forms bridges between copper atoms coordinating through both carboxylic oxygens. This entirely new copper(II) complex exhibits interesting features, such as the rare mode of coordination of the sulfato group and the threefold bridge of the hydroxo group.