Ba 6 Zn 6 (B 3 O 6 ) 6 (B 6 O 12 ): 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.

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.