AKTeO 2 (CO 3 ) (A = Li, Na): The First Carbonatotellurites Featuring a Zero-Dimensional [Te 2 C 2 O 10 ] 4- Cluster and a Wide Band Gap.

The first carbonatotellurites, AKTeO 2 (CO 3 ) (A = Li, Na), have been successfully synthesized by using boric acid as the mineralizer. AKTeO 2 (CO 3 ) (A = Li, Na) crystallize in the monoclinic space group P 2 1 / n (no. 14), and their structures exhibit the novel zero-dimensional (0D) [Te 2 C 2 O 10 ] 4- clusters, in which two [TeO 4 ] 4- groups form a [Te 2 O 6 ] 4- dimer via edge-sharing, with each side of the dimer attached by a [CO 3 ] 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 LiKTeO 2 (CO 3 ) (LKTC) and NaKTeO 2 (CO 3 ) (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 π-conjugated anionic groups reported. Theoretical calculations revealed that they exhibit moderate birefringences of 0.029 and 0.040@1064 nm, respectively.