BaZn3(BO3)2F2: a new beryllium-free zincoborate with a KBBF-type structure

A new beryllium-free zincoborate, BaZn3(BO3)2F2, with a KBBF-type structure has been synthesized for the first time. The electrostatic force of interaction in BaZn3(BO3)2F2 provides better linkage in neighboring [ZnBO3F]∞ single layers. BaZn3(BO3)2F2 is the first case of borates with both [ZnO3F] tetrahedra and [ZnO6] octahedra, enriching the structural chemistry of borate system. All the coplanar [BO3] triangles align in the same direction with a high density, which endows BaZn3(BO3)2F2 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.