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Abstract
The three-dimensional solid-state structures of a number of organic and organotransition metal-substituted polyoxoanions of the Group V and VI transition metals have been determined by single crystal x-ray diffraction techniques. These studies were undertaken in order to determine unequivocally the bonding mode utilized by various organic and organotransition metal moieties in bonding to the surface oxygen atoms of certain polyoxoanions. The structural characterizations of the following compounds have been included: {(HCCH)Mo(,4)O(,15)F}{N(n-C(,4)H(,9))(,4)}(,3) (.) CH(,2)Cl(,2), {(HCCH)Mo(,4)O(,17)(CH)}{N(n-C(,4)H(,9))(,4)}(,3) (.) 2CH(,2)Cl(,2), {(OC)(,3)MnNb(,2)W(,4)O(,19)}{N(n-C(,4)H(,9))(,4)}(,3), {((eta)('5)-C(,5)H(,5))TiMo(,6)O(,20)Cl}{N(n-C(,4)H(,9))(,4)}(,2) (.) 2CH(,2)Cl(,2) and {((eta)('5)-C(,5)(CH(,3))(,5))RhNb(,2)W(,4)O(,19)}{N(n-C(,4)H(,9))(,4)}(,2).
The structural investigations of the two organically-substituted tetramolybdo complexes, {(HCCH)Mo(,4)O(,15)F}('3-) and {(HCCH)Mo(,4)O(,17)(CH)}('3-), indicate that the anions possess several salient structural features not present in the previously reported {CH(,2)Mo(,4)O(,14)(OH)}{N(n-C(,4)H(,9))(,4)}(,3). These features include the presence of two coordinatively unsaturated molybdenum atoms and a conformationally flexible binding cavity oriented adjacent to the incorporated "glyoxal" (OHCCHO) moiety. The anions can be described in terms of their similarity to small isolated fragments of close-packed metal oxide lattices which possess oxygen-bound organic moieties.
Polyoxoanions which possess oxygen-bound organotransition metal moieties are sought as models for catalytically active solid oxide-supported transition metal complexes. In light of the substantial theoretical and technological difficulties associated with the rigorous characterization of heterogeneous surfaces, these discrete molecular complexes may provide readily accessible information concerning surface-bound molecules. The bonding of an organotransition metal moiety to the polyoxoanionic oxygen atoms in the {((eta)('5)-C(,5)H(,5))TiMo(,6)O(,20)Cl}('2-), {(OC)(,3)MnNb(,2)W(,4)O(,19)}('3-) and {((eta)('5)-C(,5)(CH(,3))(,5)RhNb(,2)W(,4)O(,19)}('2-), anions has been shown to cause a profound structural perturbation in the bond pattern observed within the anion. The structural consequences of the substitution process are discussed.
