1. For recent reviews, see: (a)Molybdenum Enzymes, Cofactors, and Model Systems; Stiefel, E. I., Coucouvanis, D., Newton, W. E., Eds.; ACS Symposium Series, Vol. 535; American Chemical Society: Washington, DC, 1993. (b) Young, C. G.; Wedd, A. G. InEncyclopedia of Inorganic Chemistry; King, R. B., Ed.; Wiley: U.K., 1994; Vol. 5, pp 2330−2346. (c) Enemark, J. H.; Young, C. G.Adv.Inorg.Chem.1993,40, 1−88. (d) Hille, R.Biochim.Biophys.Acta1994,1184, 143−169.