Transition metal complexes of pyridine-N-oxides

Structure of [Ni(ONC5H5)6]2+.[1]

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 and bonding

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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

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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]

## References

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1. ^ Van Ingen Schenau, A. D.; Verschoor, C. G.; Romers, C. (1974). "The Crystal and Molecular Structure of Hexakis(pyridine-N-oxide)nickel(II) Bis(tetrafluoroborate)". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 30 (7): 1686–1694\. Bibcode:1974AcCrB..30.1686V. doi:10.1107/S0567740874005632.
2. ^ Carlin, Richard L.; De Jongh, L. J. (1986). "Structural and Magnetic Properties of Transition Metal complexes of Pyridine N-Oxide". Chemical Reviews. 86 (4): 659–680\. doi:10.1021/cr00074a001.
3. ^ Jia, Junhua; Hubberstey, Peter; Champness, Neil R.; Schröder, Martin (2009). "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". Molecular Networks. Structure and Bonding. Vol. 132\. pp. 135–161\. doi:10.1007/430_2008_9. ISBN 978-3-642-01366-9.
4. ^ Amoroso, Angelo J.; Burrows, Miles W.; Dickinson, Anthony A.; Jones, Cameron; Willock, David J.; Wong, Wing-Tak (2001). "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". Journal of the Chemical Society, Dalton Transactions (3): 225–227\. doi:10.1039/b008993l.
5. ^ Barnett, B. L.; Kretschmar, H. C.; Hartman, F. A. (1977). "Structural characterization of bis(N-oxopyridine-2-thionato)zinc(II)". Inorg. Chem. 16 (8): 1834–8\. doi:10.1021/ic50174a002.

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Coordination complexes

H donors:|

* H−
* H2
* BH4-

B donors:|

* BR−2
* BmHn

C donors:|

* R−
* RC(O)−
* HC(O)−
* CH2=CHCH−2
* C(CH2)3
* CH2=CH2
* CR=CR2
* RC2R
* C6H4
* CN−
* CO
* CO2
* C4−
* C6R6
* C60 & C70
* RNC
* =CR2
* ≡CR
* C5H−5
* C9H−7
* =C=CR2

Si donors:|

* HnSiR4−n
* R3Si−

N donors:|

* NH3
* N−3
* imidazole
* NO
* RNO
* NO−2
* py
* amino acid
* N3−
* RN2−
* RCN
* bipy
* phen
* porphyrin
* (Me3Si)2N−
* N2
* −NCS

P donors:|

* PR3
* PR−2
* PR2OH

As donors:|

* AsR3

Bi donors:|

* RnBin
* RBi

O donors:|

* H2O
* OH−
* R2O
* RO−
* O2−
* O2
* CO2−3 & HCO−3
* C2O2−4
* RCO−2
* RCONR'2
* OC(NR2)2
* acac
* R2CO
* ONO−
* NO−3
* ClO−4
* C5H5NO
* OSR2
* SO2−4
* PO3−4
* OPR3

S donors:|

* R2NCS−2
* RS−
* R2S
* R2C2S2−2
* SO2
* SO2−3
* S2O2−3
* SR2O
* NCS−

Halide donors:|

* F−
* F2
* Cl−
* Br−
* I−

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