Probing the vanadyl and molybdenyl bonds in complex vanadomolybdate structures.

A solid solution was found to exist in the quaternary Li(2)O-MgO-V(2)O(5)-MoO(3) system between the two phases Mg(2.5)VMoO(8) and Li(2)Mg(2)(MoO(4))(3). Both Mg(2.5)VMoO(8) and Li(2)Mg(2)(MoO(4))(3) are isostructural with the mineral lyonsite, and substitution according to the formula square(1/4-x/6)Li(4x/3)Mg(15/4-7x/6)V(3/2-x)Mo(3/2+x)O(12) (0 < or = x < or = 1.5, where square denotes a cation vacancy) demonstrates that a complete solid solution exits coupling the addition of molybdenum and lithium with the subtraction of cation vacancies, magnesium, and vanadium and vice versa. Vibrational Raman spectroscopy indicates that molybdenum-oxo double bonds preferentially associate with the cation vacancies.