Synthesis and transformations of alkylphosphate and alkoxysiloxide metal complexes to multicomponent oxide materials

This thesis describes the synthesis of mixed element oxide materials utilizing oxygen rich ``single-source precursor'' molecules. The key attributes of these precursor complexes are that they possess the stoichiometry of the targeted oxide material and that they can be converted to carbon free materials by mild thermal treatment. Complexes of Al, Cu, Fe, Hf, Nb, Ta, Ti, and Zr were prepared that contain tris({lcub}it tert/{rcub}-butoxy)siloxy ligands as precursors to silica based materials. The pyrolytic decomposition of these complexes occur under mild conditions, with onset temperatures to decomposition between 95 and 200{dollar}spcirc{dollar}C. The resulting metal-silica or metal oxide-silica materials contain very little carbon. The solid state transformation of Zrlbrack OSi(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb3rbracksb4{dollar} to ZrO{dollar}sb2{lcub}cdot{rcub}{dollar}4SiO{dollar}sb2{dollar} produced an open fibrous material with pores which are ca. 20 nm in diameter. The solution phase thermolysis of the various metal siloxide complexes in anhydrous organic solvents led to xerogels consisting of small spherical primary particles ({dollar}le{dollar}ca. 5 nm). These xerogels typically possess very high surface areas. The ZrO{dollar}sb2{lcub}cdot{rcub}{dollar}4SiO{dollar}sb2{dollar} materials are amorphous as initially formed, and subsequent crystallizations of tetragonal ZrO{dollar}sb2,{dollar} monoclinic ZrO{dollar}sb2,{dollar} and cristobalite occur at relatively high temperatures. The enhanced stabilization of the amorphous and tetragonal phases of zirconia, relative to those derived from many sol-gel systems, implies that these single-source precursors initially produce highly homogeneous materials and that subsequent crystallizations are to a large degree diffusion-controlled,; Careful addition of 1 or 2 equiv of water to THF solutions of Mlbrack OSi(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb3rbracksb4{dollar} (M = Zr, Hf) produced the isolable aqua complexes Mlbrack OSi(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb3rbracksb4{dollar}(H{dollar}sb2{dollar}O) and Mlbrack OSi(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb3rbracksb4{dollar}(H{dollar}sb2{dollar}O){dollar}sb2.{dollar} It is likely that the hydrolysis of Zrlbrack OSi(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb3rbracksb4{dollar}(H{dollar}sb2{dollar}O){dollar}sb2{dollar} also occurs by an associative mechanism via the tris(aqua) intermediate Zrlbrack OSi(O{dollar}sp{lcub}t{rcub}{dollar}Bu){dollar}sb3rbracksb4{dollar}(H{dollar}sb2{dollar}O){dollar}sb3.{dollar}; The reaction of ZnEt{dollar}sb2{dollar} with HO(O)P(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb2{dollar} in the presence of slight amounts of water produced good yields of the oxo-centered tetranuclear cluster Zn{dollar}sb4{dollar}({dollar}musb4{dollar}-O)lbrack O{dollar}sb2{dollar}P(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb2rbracksb6.{dollar} When this complex was heated in ethanol at 85{dollar}spcirc{dollar}C for 30 h, or dissolved in acid containing solutions, it converted to a polymer, {dollar}{lcub}{dollar}Znlbrack O{dollar}sb2{dollar}P(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb2rbracksb2{rcub}sb{lcub}rm n{rcub},{dollar} which contains zinc atoms that are linked alternately by one and then three bridging phosphate groups. Diffusion of a toluene solution of Zn{dollar}sb4(musb4{dollar}-O)lbrack O{dollar}sb2{dollar}P(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb2rbracksb6{dollar} into a dichloromethane solution of 1,6-hexanediamine produced a layered coordination network with the formula {dollar}{lcub}{dollar}Znlbrack O{dollar}sb2{dollar}P(O{dollar}sp{lcub}rm t{rcub}{dollar}Bu){dollar}sb2rbracksb2{dollar}lbrack H{dollar}sb2{dollar}N(CH{dollar}sb2)sb6{dollar}NH{dollar}sb2rbrack{rcub}sb{lcub}rm n{rcub}.{dollar} The reaction between Zn{dollar}sb4(mu...