A NEW CHARGE-DENSITY-WAVE OXIDE, LIVMOO5 AND ITS TUNGSTEN ANALOG OBTAINED BY TOPOTACTIC REDUCTION OF LIVMO(6) (M=MO,W) BRANNERITES

We report the synthesis of two new low-dimensional oxides, LiVMO(5) (M = Mo, W), which contain S = 1/2 transition-metal atoms, V-IV:3d(1) an d Mo-V:4d(1)/W-V:5d(1), by topotactic reduction of the LiVMO(6) branne rites in hydrogen. LiVMO(5) crystallizes in orthorhombic structures re lated to the parent brannerite structure. The VMO(5) network of the ne w oxides is likely to correspond to one of the A(2)X(5) structures pre dicted by A. F. Wells (Philos. Trans. R. Soc. London A, 1984, 312, 589 ). LiVMoO5 is metallic showing a charge density wave (CDW) instability around 230 K; interestingly, LiVWO5 is a paramagnetic semiconductor d own to 20 K.