Solventothermal Synthesis and Structure of Lamellar Alkali Metal Selenidostannates(IV) A4Sn4Se10·xH2O with 20- (A=Cs; x=3.2) and 36-Membered Pores (A=K, Rb; x=4.5, 1.5)

Treatment of A2CO3(A=K, Rb) with Sn and Se in an H2O/CH3OH mixture at 130°C affords reaction solutions from which respectively K4Sn4Se10·4.5H2O (1) and Rb4Sn4Se10·1.5H2O (2) can be isolated on cooling. 1 crystallizes in the rhombohedral space group R3with a=b=15.320(3) Å, c= 21.019(7) Å, Z=6, V=4272(2) Å3, 2 in the same space group with a=b=15.539(2) Å, c=21.373(4) Å, Z=6, V=4469.4(13) Å3. These isotypic phases contain lamellar 2∞[Sn4Se4−10] polyanions in which SnSe4−4and [Sn2Se6]4−molecular building units are corner-bridged into a 63net with 36-membered cavities of 1.3×1.4 nm cross-section. Cs4Sn4Se10·3.2H2O (3) can be prepared under similar mild solventothermal conditions. It crystallizes in the triclinic space group P1with a=7.235(1) Å, b=9.468(2) Å, c=11.235(2) Å, α=68.77(3)°, β=83.25(3)°, γ=84.53(3)°, Z=1, V=711.2(2) Å3. In contrast to the 2-dimensional anions of the same formula type in 1 and 2, the 2∞[Sn4Se4−10] polyanions of 3 consist of 1∞[SnSe2−3] ribbons that are corner-bridged through ditetrahedral [Sn2Se6]4−units into sheets with smaller 20-membered pores. The role of starting pH, cation size and temperature on the construction of lamellar selenidostannates(IV) are discussed.