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 {{chem2|[M(ONC5H5)6]^{2+} }} where M = Mn(II), Fe(II), Co(II), Ni(II).{{cite journal |doi=10.1021/cr00074a001|title=Structural and Magnetic Properties of Transition Metal complexes of Pyridine N-Oxide |year=1986 |last1=Carlin |first1=Richard L. |last2=De Jongh |first2=L. J. |journal=Chemical Reviews |volume=86 |issue=4 |pages=659–680 |doi-access=free }} Many variations of pyridine N-oxide are known, such as the dioxides of 2,2'- and 4,4'-2,2'-bipyridine.{{cite book |doi=10.1007/430_2008_9|chapter=Supramolecular Chemistry of 4,4′-Bipyridine-N,N′-dioxide in Transition Metal Complexes: A Rich Diversity of Co-ordinate, Hydrogen-Bond and Aromatic Stacking Interactions |title=Molecular Networks |series=Structure and Bonding |year=2009 |last1=Jia |first1=Junhua |last2=Hubberstey |first2=Peter |last3=Champness |first3=Neil R. |last4=Schröder |first4=Martin |volume=132 |pages=135–161 |isbn=978-3-642-01366-9 }} Complexes derived from the trioxide of terpyridine have been crystallized as well.{{cite journal |doi=10.1039/b008993l |title=Geometrical preferences of complexes of terpyridine N-oxide ligands: Synthesis and crystal structures of nickel(II) with terpyridine 1,1′,1″-trioxide, terpyridine 1,1″-dioxide and terpyridine 1-oxide |year=2001 |last1=Amoroso |first1=Angelo J. |last2=Burrows |first2=Miles W. |last3=Dickinson |first3=Anthony A. |last4=Jones |first4=Cameron |last5=Willock |first5=David J. |last6=Wong |first6=Wing-Tak |journal=Journal of the Chemical Society, Dalton Transactions |issue=3 |pages=225–227 }}
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 {{chem2|C5H5NOH+}}, pyridine N-oxides are weakly basic ligands. Their complexes are generally high spin, hence they are kinetically labile.
Applications
File:Zink-Pyrithion.svg, 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..{{cite journal |title= Structural characterization of bis(N-oxopyridine-2-thionato)zinc(II) |journal= Inorg. Chem. |year= 1977 |volume= 16 |issue= 8 |pages= 1834–8 |doi= 10.1021/ic50174a002 |author1=Barnett, B. L. |author2=Kretschmar, H. C. |author3=Hartman, F. A. }}