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Exploratory synthesis in the NaHSO4−CsHSO4 system, aimed at discovering novel proton conducting solids, resulted in the new compounds CsNa2(HSO4)3 and Cs2Na(HSO4)3. Single-crystal X-ray diffraction (performed at room temperature) revealed CsNa2(HSO4)3 to crystallize in the cubic space group P213 with lattice parameters a = 10.568(2) Å and Z = 4, whereas Cs2Na(HSO4)3, studied by both single-crystal neutron and X-ray methods, crystallizes in the hexagonal space group P63/m. The latter compound has lattice parameters a = 8.5712(17) and c = 9.980(2) Å, and Z = 2. The unit cell volumes are 1180.4(4) and 634.9(2) Å3, respectively, giving calculated densities of 2.645 and 3.304 mg m-3. Refinement using all observed reflections yielded a weighted residual, R w(F 2), of 0.0515 based on F 2 X-ray values for CsNa2(HSO4)3. For Cs2Na(HSO4)3 the analogous X-ray and neutron values were 0.0483 and 0.1715, respectively. Both structures contain a single, crystallographically distinct, asymmetric hydrogen bond (as confirmed by NMR investigations) and unique, three-membered (HSO4)3 rings. The geometric match between the NaO6 octahedra and the rings suggests the sodium polyhedra may serve to template the (HSO4)3 unit. In CsNa2(HSO4)3 the rings form a distorted cubic close-packed array. The Cs atoms are located within the “octahedral” sites of this array, and the Na atoms, within the “tetrahedral” sites. The rings in Cs2Na(HSO4)3 are linked together by NaO6 octahedra to form infinite Na(HSO4)3 chains that extend along [001]. The hexagonal compound exhibits disorder about the sulfate tetrahedron that suggests a P63/m → P6 phase transition may occur upon cooling.

structure structure (solids and liquids) D 2000 -003Synthesis, Structure, and Properties of Compounds in the NaHSO 4 -CsHSO 4 System. Part 1. Crystal Structures of Cs 2 Na(HSO 4 ) 3 and CsNa 3 (HSO 4 ) 3 .-Single crystals of the title compounds are grown from aqueous solutions of Cs 2 CO 3 , Na 2 CO 3 , and H 2 SO 4 . CsNa 2 (HSO 4 ) 3 crystallizes in the cubic space group P2 1 3 with Z = 4 and Cs 2 Na(HSO 4 ) 3 crystallizes in the hexagonal space group P6 3 /m with Z = 2. Both structures contain a single, crystallographically distinct, asymmetric hydrogen bond and unique, three-membered (HSO 4 ) 3 rings. The geometric match between NaO 6 and the sulfate rings suggests that the sodium polyhedra may serve to template the (HSO 4 ) 3 unit. -(CHISHOLM, CALUM R. I.; COWAN, LISA A.; HAILE, SOSSINA M.; KLOOSTER, WIM T.; Chem. Mater. 13 (2001) 8, 2574-2583; Calif. Inst. Technol., Pasadena, CA 91125, USA; EN)

Exploratory synthesis in the NaHSO4−CsHSO4 system, aimed at discovering novel proton-conducting solids, yielded the new compounds CsNa2(HSO4)3 and Cs2Na(HSO4)3. Thermal analysis demonstrated the absence of phase transitions for both compounds prior to melting. The conductivities of the two compounds vary monotonically with temperature, in a non-Arrhenius manner, from ambient to the respective melt temperatures of 398 and 413 K. At 363 K the conductivities are on the order of 10-8 Ω1-cm-1, which is comparable to that of other alkali acid sulfates. The absence of transitions to disordered, high conductivity phases, as is observed in compounds such as CsHSO4, is explained in terms of the stiffness of the Na−O bonds, which may serve to prevent rapid reorientation of SO4 tetrahedral groups.