Synthesis, Crystal Structures, Spectroscopic Characterization, and Thermal Analyses of the New Bismuth Sulfates NaBi(SO4)2·H2O and ABi(SO4)2 (A = K, Rb, Cs)

Four alkali metal bismuth sulfates, NaBi(SO 4 ) 2 · H 2 O ( 1 ) and ABi(SO 4 ) 2 [A = K ( 2 ), Rb ( 3 ), Cs ( 4 )], were successfully synthesized by hydrothermal methods. The crystal structure of 1 features a three-dimensional tunnel framework constructed by BiO 9 tri-capped trigonal prisms and SO 4 tetrahedra interconnected via common corners and edges. Compound 2 exhibits a two-dimensional 2 ∞ [Bi(SO 4 ) 2 ] – double-layered structure, assembled by one-dimensional 1 ∞ [BiS(1)O 4 ] + chains which are linked via S(2)O 4 2– tetrahedra. The isostructural compounds 3 and 4 possess a two-dimensional layered structure, and the layers being composed by BiO 8 square antiprism and SO 4 tetrahedra. The alkali metal cations are located between the layers or in the tunnels of the structures, respectively. The differences in the crystal structures of the title compounds can mainly be attributed to the different sizes of the alkali metal cations and their different coordination environments. Thermogravimetric analysis evidence that compound 1 losses one equivalent of water at 120 °C whereas the anhydrous compounds 2 – 4 are stable up to about 450, 575, and 578 °C, respectively. The solid-state UV/Vis/NIR diffuse reflectance spectra indicate bandgaps of approximately 4.48, 4.43, 3.98, and 3.96 eV for compounds 1 – 4 , respectively.