The crystal structures of WTe2and high-temperature MoTe2

The structures of WTe2 and a high-temperature monoclinic polymorph of MoTe2 have been solved by Patterson methods. Single crystals were grown by vapor transport methods. Cell dimensions, as measured on precession photographs, are for WTe2, a=6.282/~, b= 3.496/~, c= 14073 A. Similarly for MoTe2, a=6.33 A, b=3.469/~, c=13.86/~, B=93°55. Intensities were measured for both crystals from zeroand first-level Weissenberg photographs. WTe2 and MoTe2 are given the space groups Pnm21 and P21/m, respectively. Minimum function maps prepared by a superposition method gave approximate trial structures for both compounds which were refined by least-squares methods to R values of 12.5 % and 13-9 % for WTe2 and MoTe2 respectively. Both compounds are layer structures with double sheets of tellurium atoms bound together by interleaving metal atoms. An off-center positioning of metal atoms in the tellurium octahedra buckles the tellurium sheets and allows metal atoms in adjacent octahedra to approach each other. Each metal atom, therefore, has eight neighbors, six tellurium atoms and two metal atoms, and a significant amount of metal-metal bonding is introduced.