Transition metal complexes of pyridine-N-oxides

Transition metal complexes of pyridine-N-oxides encompass coordination complexes that contain pyridine-N-oxides as ligands. Particularly common are the octahedral homoleptic complexes of the type [M(ONC₅H₅)₆]²⁺ where M = Mn(II), Fe(II), Co(II), Ni(II).^[2] Many variations of pyridine N-oxide are known, such as the dioxides of 2,2'- and 4,4'-2,2'-bipyridine.^[3] Complexes derived from the trioxide of terpyridine have been crystallized as well.^[4]

Structure of [Ni(ONC₅H₅)₆]²⁺.^[1]

Structure and bonding

Pyridine-N-oxides bind to metals through the oxygen. According to X-ray crystallography, the M-O-N angle is approximately 130° in many of these complexes. As reflected by the pKa of 0.79 for C₅H₅NOH⁺, pyridine N-oxides are weakly basic ligands. Their complexes are generally high spin, hence they are kinetically labile.

Applications

Structure of zinc pyrithione, a popular antidandruff medicine.

Zinc pyrithione is a coordination complex of a sulfur-substituted pyridine-N-oxide. This zinc complex has useful fungistatic and bacteriostatic properties..^[5]