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A novel barium zinc borate contains π-conjugated [B 3 O 6 ] 3- anions and [B 6 O 12 ] 6- anion with edge-sharing BO 4 tetrahedra, Ba 6 Zn 6 (B 3 O 6 ) 6 (B 6 O 12 ), has been successfully synthesized via a high-temperature solution reaction. In its structure, the isolated planar π-conjugated B 3 O 6 groups are interconnected by ZnO 4 tetrahedra via corner sharing to construct a [Zn 3 (B 3 O 6 ) 3 ] 3- single layer parallel to the ab plane with the large Zn 3 B 6 9-member rings. Two adjacent [Zn 3 (B 3 O 6 ) 3 ] 3- single layers are interconnected by [B 6 O 12 ] 6- anions into a two-dimensional [Zn 6 (B 3 O 6 ) 6 (B 6 O 12 )] 12- double layer with 1D tunnels of Zn 4 B 8 12-member rings along the a -axis. Neighboring such double layers are packed in an A-B-A-B... fashion along the c axis, and the Ba 2+ ions act as counterbalance cations filling in the voids of double layers. All of the planar π-conjugated [B 3 O 6 ] 3- groups in Ba 6 Zn 6 (B 3 O 6 ) 6 (B 6 O 12 ) are in approximately parallel arrangement, producing large optical anisotropy and birefringence. The UV-vis-NIR absorption spectrum manifests that the UV cutoff edge for the title compound is below 200 nm. Ba 6 Zn 6 (B 3 O 6 ) 6 (B 6 O 12 ) possesses the largest birefringence (0.115@1064 nm) among the zincoborates reported. Its thermal stability, infrared spectrum, and theoretical calculations were also performed.

Two new borogermanate/borosilicate fluorides, namely, NaBa 3 [M 2 B 7 O 16 (OH) 2 ]F 2 (M = Ge, Si), have been successfully synthesized through a conventional mild hydrothermal method. They represent the first examples of mixed alkali and alkaline-earth borogermanate/borosilicate fluorides. NaBa 3 [M 2 B 7 O 16 (OH) 2 ]F 2 (M = Ge, Si) crystallize in the space group of C 2/ c , and their structures feature a unique 3D anionic framework composed of [B 7 O 16 (OH) 2 ] 13- polyanions corner-sharing with SiO 4 or GeO 4 tetrahedra, forming 1D 10-membered-ring tunnels along the b axis, which are filled by Na + , Ba 2+ , and F - ions. UV-vis-near-IR absorption spectra identify the title compounds possessing short deep-ultraviolet absorption edges (below 200 nm), while their birefringences were calculated to be 0.021 and 0.016 at 1064 nm, respectively. Optical property, thermal stability, and theoretical calculations have also been conducted on NaBa 3 [M 2 B 7 O 16 (OH) 2 ]F 2 (M = Ge, Si).

Explorations of new types of borates are important because of their promising application in diverse fields. A new bismuth-containing boroselenite, Bi 2 [B 2 (SeO 3 ) 6 ], has been obtained through high-temperature solid-state reaction in a closed system. Bi 2 [B 2 (SeO 3 ) 6 ] possesses a zero-dimensional [B 2 (SeO 3 ) 6 ] 6- anionic group that does not belong to any types of reported boroselenites. Besides, Bi 2 [B 2 (SeO 3 ) 6 ] is the first boroselenite with lone-pair electrons containing a metal ion as the countercation. More interestingly, on the basis of the first-principles calculations, this compound displays a large birefringence (0.090) at 1064 nm.