Structural Relationship Between Two Cluster Anions And One Framework Structure Of Novel Molybdenum(VI) Arsenates. Sue-Lein Wang* and Kuei-Fan Hsu, Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043

\par The utilization of hydrothermal and flux-growth techniques to the synthesis of molybdenum(VI) arsenic(V) oxide phases have allowed us to isolate several series of novel compounds with molecular, 1-D, 2-D, and 3-D open framework structures. For example, the molybdenum monoarsenates, AxMoO2AsO4 (A = Li, Na, K, Sr, Ba; x = 1 or 0.5) are layer structures; the two diarsenates, Rb2(MoO2)3(As2O7).2H2O and Cs2Mo2O5As2O7.H2O possess very large tunnels where water molecules from humidity are residing; and the two molecular species Cs2Mo2O5(HAsO4)2.H2O and Cs4Mo6O18(H2O)(HAsO4)2 .2H2O contain cluster anions of edge-sharing or face-sharing MoO6 octahedra It is interesting to note that upon heating, the above-mentioned cluster anion-containing arsenates will transform to framework structure, i.e. discrete cluster anions in both compounds Cs4Mo6O18(H2O)(HAsO4)2 .2H2O and Cs2Mo2O5(HAsO4)2.H2O fuse together to give the large tunnel structure of Cs2Mo2O5As2O7.H2O. In this presentation, reaction fators controlling the formation of these three phases and structural characterization of these new compounds are given. Structural relationship between the two molcular solids, Cs4Mo6O18(H2O)(HAsO4)2 .2H2O and Cs2Mo2O5(HAsO4)2.H2O and the 3-D framework structure Cs2Mo2O5As2O7.H2O are discussed in detail.