Design and Syntheses of Three Novel Carbonate Halides: Cs3Pb2(CO3)3I, KBa2(CO3)2F, and RbBa2(CO3)2F

Three new carbonate halides, Cs3 Pb2 (CO3 )3 I, KBa2 (CO3 )2 F and RbBa2 (CO3 )2 F have been synthesized with hydrothermal and solid-state methods. Cs3 Pb2 (CO3 )3 I is the first product in the lead carbonate iodides family; KBa2 (CO3 )2 F and RbBa2 (CO3 )2 F are the first two centrosymmetric compounds found in the alkaline-alkaline earth carbonate fluorides family. Cs3 Pb2 (CO3 )3 I crystallizes in a centrosymmetric space group C2/m, and exhibits a two- dimensional layered structure which is formed by [Cs4 Pb4 (CO3 )6 I2 ]∞ double-layers consisting of [Pb2 (CO3 )3 I]∞ single-layers bridged by the Cs atoms. KBa2 (CO3 )2 F and RbBa2 (CO3 )2 F, which are isostructural, crystallize in a trigonal crystal system with a centric space group of R3‾ featuring a honeycomb-like framework. First principle calculations indicate that Cs3 Pb2 (CO3 )3 I has a moderate birefringence and explain the difference between the band gaps of the title compounds from electron structures. The effects of cations and halogens on the structures and properties of the title compounds are also discussed.