FORMATION AND ION-EXCHANGE CHEMISTRY OF NEW OXIDES WITH THE HEXAGONAL MOO3 STRUCTURE

In dilute acid solution, layered oxides AVMoO6 (A = Li, Na) with the "brannerite" structure do not undergo the expected ion-exchange reaction to produce HVMoO6, and instead participate in an unusual "leaching reaction" that leads to the formation of new compounds with the stoichiometry A0.13V0.13Mo0.87O3 (A = H.2H2O, Na.2H2O). These well crystallized products have the "hexagonal MoO3" structure, which contains one-dimensional tunnels with free diameters approaching 3.5 angstrom. Complete dehydration of the product of the Li brannerite reaction, (H.2H2O)0.13V0.13Mo0.87O3 produces V0.13Mo0.87O2.935, which retains the "hexagonal MoO3" Structure up to 455-degrees-C and has empty tunnels. This microporous phase readily undergoes a variety of ion-insertion reactions. Hexagonal (LixH1-x)0.13V0.13Mo0,87O3.nH2O has also been prepared by direct precipitation from lithium molybdov-anadate solutions. (H.2H2O)0.13V0.13Mo0.87O3 and (Li.2H2O)0.13V0.13Mo0.87O3 have been obtained from these precipitates by ion-exchange. Upon heating, Li0.13V0.13Mo0.87O3 undergoes an exothermic transformation in which the dehydrated Li ions "hop" from the tunnel sites to trigonal prismatic sites located in the framework.