ABSTRACT
The chemistry discussed here is largely restricted to the complexes in which the basic backbone structure of the oligomers is not changed, such as by generation of multiple bonds between the vanadium centers. The coordination number and geometry of the individual vanadiums, however, might well be influenced by coordination. In this sense, then, the oligovanadates do not generally display the rich chemistry found with the monomer. One of the reasons for this is that in order for, for instance, divanadate to form, two VOH bonds condense, with the elimination of water and formation of the VOV linkage. The result is the loss of a reactive center at each vanadium. To an extent, this may be compensated for by expansion of the coordination sphere. Many of the known V
complexes have pentacoordinate geometry and a [VO]
cyclic core that distinguishes such complexes from divanadate, where the vanadiums have tetrahedral coordination and are linked through a single bridging oxygen. Complexes having the cyclic core have previously been discussed (Section 4.1). Divanadate displays much of the chemistry associated with monodentate ligation of the monomer with reaction occurring at the OH functionalities. Thus, for instance, alcohols replace hydroxyl groups in a systematic manner to give alkyldivanadates [1]. Unfortunately, divanadate chemistry generally is difficult to study in detail because reactants are not specific to divanadate, and almost invariably the chemistry of the monomer dominates.
