AKTeO2(CO3) (A = Li, Na): The First Carbonatotellurites Featuring a Zero-Dimensional [Te2C2O10]4-Cluster and a Wide Band Gap

The first carbonatotellurites, AKTeO2(CO3) (A = Li, Na), have been successfully synthesized by using boric acid as the mineralizer. AKTeO2(CO3) (A = Li, Na) crystallize in the monoclinic space group P21/n (no. 14), and their structures exhibit the novel zero-dimensional (0D) [Te2C2O10]4- clusters, in which two [TeO4]4- groups form a [Te2O6]4- dimer via edge-sharing, with each side of the dimer attached by a [CO3]2- group via a Te-O-C bridge. The alkali metal cations occupy the voids between the 0D clusters and maintain the charge balance. The ultraviolet-visible-near-infrared diffuse reflectance spectra show that the short absorption cut-off edges of LiKTeO2(CO3) (LKTC) and NaKTeO2(CO3) (NKTC) are 248 and 240 nm, respectively, and LKTC exhibits the largest experimental band gap (4.58 eV) among all of the tellurites containing the pi-conjugated anionic groups reported. Theoretical calculations revealed that they exhibit moderate birefringences of 0.029 and 0.040@1064 nm, respectively.