Use of hydrothermal methods for the synthesis of metal molybdates, copper carboxylates and molybdenum phosphates

Abstract

In this work, hydrothermal reactions were studied as a synthetic method in three systems: metal molybdates, copper carboxylates and molybdenum phosphates. Different solvents were used in each system studied to determine if any underlying trends could be observed in hydrothermal reactions. In each system at least one compound was found that had not been previously observed in either reflux or solid state reactions. Transition metal oxides and molybdenum oxides were reacted hydrothermally in neutral, slightly basic (0.5 M NaOH) and mildly acidic (0.5 M acetic acid) aqueous solutions. The reaction products were compared to known compounds listed in the ASTM powder diffraction files that were synthesized by traditional solid state reactions and reflux reactions. In the second system, copper oxide was reacted with glacial acetic acid to form two different copper acetate phases at different locations in the reaction tube. Single crystal structure determinations of the products indicated the formation of the anhydrous copper acetate at the solvent free end of the tube while the formation of the copper acetate monohydrate, where a solvent molecule is incorporated into the structure, formed in the solvent end of the tube. The hydrothermal reactions of molybdenum oxides were conducted in 85% phosphoric acid. In some of these reactions either Na2HPO4 or K2HPO4 was add to the starting mixture of molybdenum oxides. Three new layered molybdenum phosphates, K(MoO2OH)HPO4, MoOPO4*2.5H2O and Na2(MoOPO4)2HPO4-2H2O, were synthesized and one of these, K(MoO2OH)HPO4 was found to undergo a topotatic reaction to form KMoO2PO4. A single crystal structure was determined for each compound. While each system was unique, a comparison of reaction products indicates that a few underlying trends are observed in hydrothermal reactions. Systematic reaction characteristics are discussed in the final chapter.