LOCAL ORDER AND METAL-METAL BONDING IN LI2MOO3, LI4MO3O8, LIMOO2, ANDH2MOO3, DETERMINED FROM EXAFS STUDIES

Molybdenum K-edge EXAFS studies have allowed us to determine the local order in the layered materials Li2-MoO3, Li4Mo3O8, LiMoO2, and H2MoO3 . The presence of Mo3 metal-metal-bonded triangles in Li2MoO3, with d( Mo-Mo) = 2.580(1) angstrom (x 2), is unequivocally demonstrated for th e first time. This information cannot be obtained from diffraction exp eriments because the system is intrinsically disordered. Triangular cl usters are also found in the related Mo(IV)-containing lithium molybda te Li4Mo3O8 and in H2MoO3, prepared from Li2MoO3 by ion exchange (d(Mo -Mo) = 2.560(1) angstrom (x 2) and 2.506(1) angstrom (x 2), respective ly). The metal-metal bonding in the Mo(III)-containing oxide LiMoO2 is shown to be more complex than diffraction studies had indicated. In L iMoO2, Mo-Mo-bonded chains are formed, and we present a possible model containing disordered chains, with d(Mo-Mo) = 2.561(2) angstrom (x 2) and 2.709(2) angstrom (x 2), found in the MoO2 sheets.