NONSTOICHIOMETRY IN THE LIMO2O3(PO4)(2) STRUCTURE - THE MOLYBDENOTUNGSTEN MONOPHOSPHATE LI0.5MOWO3(PO4)(2)

A new molybdenotungsten monophosphate, Li0.5MoWO3(PO4)(2) has been syn thesized that crystallizes in the space group P2(1)/m with a = 7.735(1 ) Angstrom, b = 12.655(1) Angstrom, c = 8.324(1) Angstrom, b = 105.97( 1)degrees. The [MoWP2O11](infinity) framework is isotypic with that pr eviously observed for LiMo2O3(PO4)(2), lithium being located in six-si ded tunnels running along (a) over right arrow with an octahedral coor dination. This phase differs from LiMo2O3(PO4)(2), by the absence of l ithium in the tetrahedral sites, showing that a significant lithium no nstoichiometry is possible. The stability is discussed with respect to other lithium monophosphates LiMoWO3(PO4)(2) and Li0.2Mo2O3(PO4)(2) t hat have different original structures.