AN UNUSUAL COMPLEX DERIVED FROM MOCL3(THF)3 AND AGBF4 IN ACETONITRILE - SYNTHESIS AND STRUCTURE OF [MO2(MU-F)(NCCH3)8O2][BF4]3

Reaction of MoCl3(THF)3 with 3 equiv of AgBF4 in refluxing acetonitrile produces the unusual solvated Mo(IV)-oxo complex [Mo2(mu-F)(NCCH3)8O2][BF4]3 (1) as a result of oxidation by silver(I), as well as abstraction of both a fluoride ion from [BF4]- and an oxygen atom from THF or adventitious water. Compound 1 has been investigated by H-1 and F-19 NMR, IR and UV-vis spectroscopy, electrochemistry and X-ray crystallography. Single crystal X-ray data collected at -92 +/- 2-degrees-C revealed that 1 is monoclinic, space group P2/n with a = 11.776(4), b = 12.293(7), c = 12.497(7) angstrom, beta = 100.90(4)-degrees, V = 1776(1) angstrom 3 and Z = 2. Final refinement led to R = 0.038 and R(W) = 0.059. The structural core of the molecule consists of the unusual group [O = Mo-F-Mo = O]3+ for which the angle Mo-F-Mo is 165.0-degrees. The pyramidal MoN4 units around each molybdenum(IV) centre are staggered with respect to one another, and as a result of the basal N plane being 0.27 angstrom from the molybdenum centre, the acetonitriles are canted towards the centre of the molecule forming a ''cupped'' central region around the bridging fluorine atom. This fluoride-bridged structur is unique among molybdenum(IV) dimers, and is one of only several documented examples in molybdenum chemistry.