HYDROTHERMAL SYNTHESIS AND STRUCTURE OF NEW FRAMEWORK MOLYBDENUM (VI) ARSENATES. Kuei-Fang Hsu, Sue-Lein Wang^*, Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043

A large number of new compounds have been synthesised and structurally characterized in the A-Mo-P-O system where A is an alkali or alkaline-earth metal and Mo is in the oxidation states below VI. In contrast to the rich structural chemistry of molybdenum phosphates, little is known about their arsenate analogues. As a part of our research program to study the structural chemistry of transistion-metal arsenates, we began to synthesise new compounds in the A-Mo^VI-As^V-O system using hydrothermal techniques. By incorporating either organic or hydrated inorganic cations in the hydrothermal reactions, novel frameworks have been produced. In this presentation, the synthesis and crystal structures of three series of molybdenum(VI) arsenates will be given. They include: (1) A₂Mo₂O₅(HAsO₄)₂.H₂O (A = Cs and C₅H₅NH); (2) A₅[Mo₄O₁₂ (OH)]₂AsO₄.2H₂O (A = Rb and Cs), and the thermal decomposition product Cs₇(MoO₃)O₂AsO₄; and (3) SrMoO₃(HAsO₄).H₂O and Ba(MoO₃)₆(AsO₄)₄(H₂O). Structural relationship among some of these molybdenum arsenates is also discussed.