MO K-EDGE EXAFS AND S K-EDGE ABSORPTION STUDIES OF THE AMORPHOUS MOLYBDENUM SULFIDES MOS4.7, MOS3, AND MOS3-CENTER-DOT-NH(2)0 (N-SIMILAR-TO-2)

Molybdenum K-edge EXAFS measurements on the new amorphous sulfide, MoS4.7, and the known amorphous sulfides, MoS3 and MoS3 . nH(2)O (n similar to 2), have yielded information on the coordination around molybdenum in these compounds. The results for MoS3 and its hydrates, MoS3 . nH(2)O (n = 1.7, 2.1, and 2.2), prepared using a number of different methods, show that the coordination around molybdenum is the same in all of these materials. In MoS3 and MoS3 . nH(2)O, molybdenum is surrounded by six sulfurs at similar to 2.43 Angstrom and is also bonded to a molybdenum at 2.76 Angstrom. No evidence was found for the longer Mo-Mo distance of similar to 3.2 Angstrom in MoS3 which has been reported by other workers. There is evidence that the Mo-S bond lengths are inequivalent but not as markedly different as has been suggested previously. Our results suggest that the models for MoS3 presented in the literature to date may be incorrect. The local structure around molybdenum in MoS4.7 differs from that in MoS3. The most important differences are that the average number of sulfur atoms around each molybdenum in MoS4.7 is higher than in MoS3 and that the Mo-Mo coordination number is greater. Our structural model for MoS4.7 takes account of this with an average 7 1/3 sulfurs around each molybdenum and an average Mo-Mo coordination number of 1 1/3. EXAFS analysis and infrared spectroscopy are consistent with the formulation of MoS3 as Mo-V(S2-)(2)(S-2(2-))(0.5) and MoS4.7 as Mo-4.7(S-2(2-))(2.35). Sulfur K-edge absorption spectra for MoS3, MoS4.7, sulfur, and the model compound VS4 are in agreement with these formulations and assignment of oxidation states. Comparisons with crystalline materials are made and possible models of the structures presented.