Study on Synthesis and Structural Chemistry of Tungstate Family Using Host-Guest Reactions

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The host-guest reaction can create metastable isomorphic or polymorphic forms which cannot be prepared by the ordinary synthetic methods, i. e., fusion, solid-state reaction, hydrothermal techniques and so on. Thus, the unique functions are expected to be manifested in the new compounds. In this study, the host-guest reactions on tungstate family have been investigated.1. Interlayer Na^+ions in Na_2W_4O_<13> with layer structure were found to be topotactically exchanged for univalent cations in molten nitrate salts. Consequently, new Li_2W_4O_<13>, K_2W_4O_<13> and Rb_2W_4O_<13>, which are isostructural with Na_2W_4O_<13>, were successfully synthesized. The Li_2W_4O_<13> showed much lower ionic conductivity than the original Na_2W_4O_<13>.2. K^+ions in K_2W_4O_<13> with its tunnel framework structure were found to be topotactically exchanged for univalent cations in molten nitrate salts. Consequently, new LiKW_4O_<13>, Na_<1.4>K_<0.6>W_4O_<13>, Rb_<0.8>K_<1.2>W_4O_<13>, and Ag_<1.5>K_<0.5>W_4O_<13>, which are isostructural with K_2W_4O_<13>, were successfully synthesized. Proton-exchanged potassium tungstates (H_<0.25>K_<1.75>W_4O_<13>), which is isostructural with K_2W_40_<13>, were also found to have the feasibility of the potassium memorized exchangers.3. The cation-exchanges of K_2Mn_4O_8 in aqueous solutions and molten salts revealed to be able to produce new hydrous R_2Mn_4O_8・nH_2O (R=Li, Na, Ag, and NH_4 ; n=1-2) and anhydrous R_2Mn_4O_8 (R=Li, Na, and NH_4) with layer structures.