Date of Award
Doctor of Philosophy
Robert E. McCarley
This research effort focused on the use of both inorganic solution syntheses of molecular precursors and solid state reactions involving molecular compounds to yield desired condensed materials. Two types of molecular compounds have been investigated. First, trichloronitridotungsten(VI) ((WNCl[subscript]3] [subscript]4) has been prepared using an improved synthetic approach and characterized structurally by single crystal X-ray diffraction techniques. (WNCl[subscript]3] [subscript]4 crystallizes in the space group P1 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. The reactivity of WNCl[subscript]3, with nitriding agents, such as ammonia, ytrimethylsilylazide and lithium nitride, has been investigated, which resulted in the preparation and spectroscopic identification of new tungsten azido and nitrido compounds. Second, the reactivity of the metal dimers Mo[subscript]2(O[subscript]2CCH[subscript]3)[subscript]4 and Mo[subscript]2Cl[subscript]4py[subscript]4 with trimethylsilylazide has been explored, and the reactions in pyridine were found to yield a material corresponding to the formulation, MoN(N[subscript]3)py. Thermolytic decomposition of this azide at 280°C was performed under argon, dynamic vacuum or ammonia. The thermal decomposition in ammonia was found to produce a molybdenum nitride relatively free of carbon (5%, compared to 24% in materials decomposed in inert environments) with a Mo:N ratio of 1:1.8;Through the use of solid state reactions, WNCl[subscript]3 was converted into a hexagonal ammonium tungsten bronze, (NH[subscript]4)[subscript]0.28WO[subscript] 3-y(NH)[subscript] y. Relative to conventional preparations, this new ammonium bronze synthesis increased the probability of isoelectronic imido substitution for oxide in the bronze framework. Rietveld refinements of neutron powder data, for this bronze, indicated strongly that nitrogen, in the form of imide, does not substitute for oxygen (i.e., y = 0 in the previous formulation). A model for ammonium cation motion in the hexagonal channels for 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 hexagonal bronze phases that are metallic conductors.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Michael Richard Close
Close, Michael Richard, "New pathways to tungsten and molybdenum oxides, nitrides and azides " (1992). Retrospective Theses and Dissertations. 10104.