BaZn 3 (BO 3 ) 2 F 2 : a new beryllium-free zincoborate with a KBBF-type structure

A new beryllium-free zincoborate, BaZn 3 (BO 3 ) 2 F 2 , with a KBBF-type structure has been synthesized for the first time. The electrostatic force of interaction in BaZn 3 (BO 3 ) 2 F 2 provides better linkage in neighboring [ZnBO 3 F] ∞ single layers. BaZn 3 (BO 3 ) 2 F 2 is the first case of borates with both [ZnO 3 F] tetrahedra and [ZnO 6 ] octahedra, enriching the structural chemistry of borate system. All the coplanar [BO 3 ] triangles align in the same direction with a high density, which endows BaZn 3 (BO 3 ) 2 F 2 with a large birefringence of cal. 0.076 at 1064 nm. This work is of great significance to design beryllium-free borates with a KBBF-type structure.