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

Abstract Three new carbonate halides, Cs 3 Pb 2 (CO 3 ) 3 I, KBa 2 (CO 3 ) 2 F and RbBa 2 (CO 3 ) 2 F have been synthesized with hydrothermal and solid‐state methods. Cs 3 Pb 2 (CO 3 ) 3 I is the first product in the lead carbonate iodides family; KBa 2 (CO 3 ) 2 F and RbBa 2 (CO 3 ) 2 F are the first two centrosymmetric compounds found in the alkaline–alkaline earth carbonate fluorides family. Cs 3 Pb 2 (CO 3 ) 3 I crystallizes in a centrosymmetric space group C 2/ m , and exhibits a two‐ dimensional layered structure which is formed by [Cs 4 Pb 4 (CO 3 ) 6 I 2 ] ∞ double‐layers consisting of [Pb 2 (CO 3 ) 3 I] ∞ single‐layers bridged by the Cs atoms. KBa 2 (CO 3 ) 2 F and RbBa 2 (CO 3 ) 2 F, which are isostructural, crystallize in a trigonal crystal system with a centric space group of R featuring a honeycomb‐like framework. First principle calculations indicate that Cs 3 Pb 2 (CO 3 ) 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.