THE STRUCTURES OF THE NEW AMORPHOUS TRANSITION-METAL CHALCOGENIDES MOS4.65, WS5 AND CRSE3

Neutron diffraction studies have been made on the newly discovered amorphous transition metal sulfides, MoS4.65, and WS5, and the amorphous selenide, CrSe3. Structure factor data have been transformed to yield the total correlation function T(r). The first four peaks in the T(r) data for the sulfides, MoS4.65 and WS5, at around 2.0 Angstrom, 2.4 Angstrom 2.9 Angstrom and 3.4 Angstrom are ascribed to the S-S bond length in disulfide (S-2(2-1)) groups, the metal-sulfur bond, a metal-metal bond and the first non-bonded S-S distance, respectively. Over a similar range of T(r), the chromium selenide, CrSe3, shows only two peaks at 2.46 Angstrom and 3.64 Angstrom. In this case, the first peak is made up of a contribution from both the Se-Se distance in diselenide (Se-2(2-)) groups and the metal to selenium bond distance. The second peak corresponds to the first non-bonded Se-Se distances. We conclude that the basic structural unit in all these compounds is the octahedral MX(6) group (X = S or Se), and that all the sulfur is found in S-2(2-) groups. CrSe3 is more complicated containing both Se2- and Se-2(2-) groups.