Background Chemistry of Molybdenum

Molybdenum chemistry and biochemistry

Molybdenum is the fourth member of the second transition series and is placed with chromium and tungsten in Group 6 of the Periodic Table. In its chemical properties molybdenum resembles tungsten and vanadium, the first member of Group 5, rather than chromium. Chemically molybdenum is versatile, forming compounds in a range of readily interconvertible oxidation states, complexes with many inorganic and organic ligands including physiologically important compounds, binuclear and polynuclear species involving bridging ligands (oxide, hydroxide, sulfide) or direct metal-metal bonds between molybdenum atoms, and compounds in which the molybdenum coordination number ranges from four to eight.

P.C.H. Mitchell, Chemical and Engineering News, 2003, 81, 108: Molybdenum.
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Mitchell, P. C. H. et al., (eds.), Proceedings of the Climax International Conferences on the Chemistry and Uses of Molybdenum, Climax Molybdenum Co. Ltd., London and Ann Arbor: First 1973, Second 1976, Third 1979, Fourth 1982, Fifth 1985.
Mitchell, P.C.H., in Ullmann’s Encyclopedia of Industrial Chemistry, 5th Ed., 1990, A 16, Chap. 7, pp 675 - 682 and references therein.

In biological systems molybdenum is an essential constituent of enzymes [Stiefel, 2002; Williams and da Silva, 2002] which catalyse redox reactions, e.g. oxidation of aldehydes, xanthine and other purines [Stiefel, 1996; Schindelin et al., 1996], and reduction of nitrate and molecular nitrogen. [Sellman, 1993; Kim et al., 1993; Burris and Roberts, 1993]. The biochemical importance of molybdenum is due to its ability (a) to provide facile electron-transfer pathways, a consequence of the easy interconvertibility of different oxidation states, (b) to form bonds with nitrogen-, oxygen-, and sulfur-donors which are sufficiently strong to permit the existence of stable complexes but also sufficiently labile to permit facile ligand exchange reactions or changes of molybdenum co-ordination number (as when interacting directly with a substrate).

Stiefel, E.I., The biogeochemistry of molybdenum and tungsten, Molybdenum and Tungsten: Their Roles in Biological Processes, 2002, 39, 1-29.
Williams, R.J.P. and da Silva, J. J. R. F., The involvement of molybdenum in life, Biochemical and Biophysical Research Communications, 2002, 292, 293-299.
Stiefel, E.I., Science, 1996, 272, 1599.
Schindelin, H., Kisker, C., Hilton, J., Rajagopalan, K. V.and Rees, D. C., Science , 1996, 272, 1615.
Sellmann, D., Angewandte Chemie-International Edition, 1993, 32, 64-67.
Kim. J, Woo. D, Rees .D. C., Biochemistry, 1993, 32, 7104.
Burris, R.H., Roberts, G.P., Annual Review of Nutrition, 1993, 13, 317-335.