The chemistry of molybdenum has been aptly described as among the
most complex of the transition elements (1). The formal oxidation states
range from -2 to +6, with extensive chemistry within states 0, 2, 3, 4, 5, and
6. Coordination numbers span from four to eight, and mononuclear, dinu￾clear, and polynuclear or polymeric compounds are known in virtually all
oxidation states. Some of these myriad possibilities have been selected for use
by living things, and Mo has been shown to be a key component of several
enzymes. Despite an intensifying interest over the last 10 years, it is our feeling
that there remains a great deal to learn about the coordination chemistry and
especially the biochemistry of molybdenum. Primarily, this review deals with
the coordination chemistry of Mo. Emphasis is placed on recent progress, but
some problems (old and new) and unsettled areas are delineated as well. A
second theme falls in the area of bioinorganic chemistry, and in some cases
discussions of coordination chemistry are viewed in the light of biochemical
considerations.