New pathways to tungsten and molybdenum oxides, nitrides and azides

Thesis/Dissertation · Wed Oct 07 04:00:00 EDT 1992

OSTI ID:10108296

Close, M R

[WNCl{sub 3}]{sub 4} was prepared and characterized structurally by X-ray diffraction. [WNCl{sub 3}]{sub 4} crystallizes in space group P{bar 1} as planar 8-membered W-N rings interconnected through chloride bridges. The inter-tetramer linkage is weak and broken easily to accommodate basic ligands in the site trans to the W-N triple bond. Reactivity of WNCl{sub 3}, with nitriding agents, such as ammonia, trimethylsilylazide and lithium nitride, has been investigated, which resulted in preparation of new tungsten azido and nitrido compounds. Second, the reactivity of the metal dimers MO{sub 2}(O{sub 2}CCH{sub 3}){sub 4} and MO{sub 2}Cl{sub 4}py{sub 4} with trimethylsilylazide has been explored, and the reactions in pyridine were found to yield a material corresponding to the formulation, MoN(N{sub 3})py. Thermolytic decomposition of this azide at 280{degree}C was performed under argon, dynamic vacuum or ammonia. Thermal decomposition in ammonia produces a molybdenum nitride relatively free of carbon with a Mo:N ratio of 1:1.8. WNCl{sub 3} was converted into a hexagonal ammonium tungsten bronze, (NH{sub 4}){sub 0.28}WO{sub 3-y}(NH){sub y}. This synthesis increased the probability of isoelectronic imido substitution for oxide in the bronze framework. Rietveld refinements of neutron powder data indicated strongly that nitrogen, in the form of imide, does not substitute for oxygen. A model for ammonium cation motion in the hexagonal channels of the bronze was developed. Electrical resistivity measurements on a pressed pellet of this hexagonal bronze show a temperature dependence like that of a low-band gap semiconductor, in contrast to conventionally prepared metallic hexagonal bronze phases.

• Research Organization: Ames Lab., IA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 10108296
• Report Number(s): IS-T--1608; ON: DE93003051
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201
AMIDES
AMMONIUM COMPOUNDS
AZIDES
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES
ELECTRIC CONDUCTIVITY
HEXAGONAL LATTICES
INFRARED SPECTRA
MOLYBDENUM COMPLEXES
MOLYBDENUM NITRIDES
NITROGEN COMPOUNDS
PREPARATION AND FABRICATION
PYRIDINE
PYROLYSIS
SYNTHESIS
TUNGSTATES
TUNGSTEN CHLORIDES
TUNGSTEN COMPLEXES
TUNGSTEN NITRIDES
X-RAY DIFFRACTION