An Antimony (III) Borate with Large Birefringence Exhibiting Unwonted [B5O11] Fundamental Building Block and Dimeric [Sb2O6] Cluster

A new birefringent crystal SbB5O9 has been synthesized by combining π-conjugated [B3O6] groups and Sb3+ cations with SCALP. It exhibits the unwonted [B5O11] fundamental building block (FBB) and dimeric [Sb2O6] cluster. Remarkably, SbB5O9 exhibits a short UV cutoff edge (below 240 nm) and a large birefringence (Δn = 0.151 @ 1064 nm) which is even better than that of the well-known commercial birefringent material α-BaB2O4 (α-BBO) (Δn = 0.122 @ 532 nm). First-principles calculations show that the birefringence enhancement mainly originates from the highly distorted [Sb2O6] dimer and π-conjugated B–O anionic groups.