Ba<sub>6</sub>Zn<sub>6</sub>(B<sub>3</sub>O<sub>6</sub>)<sub>6</sub>(B<sub>6</sub>O<sub>12</sub>): Barium Zinc Borate Contains π-Conjugated [B<sub>3</sub>O<sub>6</sub>]<sup>3–</sup> Anions and [B<sub>6</sub>O<sub>12</sub>]<sup>6–</sup> Anion with Edge-Sharing BO<sub>4</sub> Tetrahedra
Weijie Xie, Zhi Fang, Jiang‐Gao Mao
Abstract
A novel barium zinc borate contains π-conjugated [B3O6]3– anions and [B6O12]6– anion with edge-sharing BO4 tetrahedra, Ba6Zn6(B3O6)6(B6O12), has been successfully synthesized via a high-temperature solution reaction. In its structure, the isolated planar π-conjugated B3O6 groups are interconnected by ZnO4 tetrahedra via corner sharing to construct a [Zn3(B3O6)3]3– single layer parallel to the ab plane with the large Zn3B6 9-member rings. Two adjacent [Zn3(B3O6)3]3– single layers are interconnected by [B6O12]6– anions into a two-dimensional [Zn6(B3O6)6(B6O12)]12– double layer with 1D tunnels of Zn4B8 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 Ba2+ ions act as counterbalance cations filling in the voids of double layers. All of the planar π-conjugated [B3O6]3– groups in Ba6Zn6(B3O6)6(B6O12) 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. Ba6Zn6(B3O6)6(B6O12) possesses the largest birefringence (0.115@1064 nm) among the zincoborates reported. Its thermal stability, infrared spectrum, and theoretical calculations were also performed.