Sr5(CO3)2(BO3)2: A new family member of isostructural mixed borate and carbonate Ba4M(BO3)2(CO3)2 (M = Ba, Sr) with isolated BO3 and CO3 groups

A new mixed borate and carbonate Sr 5 (CO 3 ) 2 (BO 3 ) 2 , which is isostructural with Ba 4 M(BO 3 ) 2 (CO 3 ) 2 (M = Ba, Sr), has been synthesized by hydrothermal method . It crystallizes in Pnma (No. 61) space group with the lattice parameters a  = 7.387(4), b  = 16.556(9) and c  = 8.971(5) Å ( Z  = 4). This structure features a three-dimensional (3D) network including SrO 8 polyhedra, isolated BO 3 and CO 3 triangles. UV-Vis-NIR diffuse reflectance spectrum for Sr 5 (CO 3 ) 2 (BO 3 ) 2 indicates that it has a deep ultra-violet cut-off edge of 190 nm. In addition, crystal structural comparison among mixed borates and carbonates shows that the interaction between boron-oxide groups and CO 3 groups leads to different arrangements of anionic groups, which can be classified into three types according to the connection of boron-oxide groups. An analysis of theoretical calculations based on density functional theory was also performed to understand the relationships between the structures and properties.