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Crystals of magnesium oxomethoxoniobate, Mg2Nb2O2(OMe)10(MeOH)4 (1), resulting from partial decomposition of bimetallic alkoxoniobate, MgNb2(OMe)12·2MeOH (2), have been isolated with moderate yields from solutions obtained by interaction of magnesium and niobium methoxides in MeOH. Compound 1 is a non-volatile product, insoluble in hydrocarbons and poorly soluble in alcohol. The structure of its molecule is analogous to that of Ti4(OMe)16, the positions connected to two tridentate OR-groups being occupied by Mg atoms and those connected to one tridentate—OR-group—by those of Nb. The analysis of the MO bond lengths permits 1 to be considered as [Mg(ROH)2]2 2+ [NbO(OR)5]2 2−. Compound 2 in analogy to the corresponding tantalum derivative is a non-crystallizing viscous volatile liquid. Its mass-spectrum contains the products corresponding to elimination of Nb(OR)5 and R2O. The structural difference for niobium and tantalum oxoalkoxides can be explained by the ability of only niobium atoms to form terminal bonds to oxygen atoms (‘niobyl’ groups). |
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