Sn2B5O9Br as an Outstanding Bifunctional Material with Strong Second‐Harmonic Generation Effect and Large Birefringence

Abstract The first tin (II) borate bromide, Sn 2 B 5 O 9 Br (SBOB), as an outstanding bifunctional material with excellent linear and nonlinear optical (NLO) performance is synthesized successfully. As far as it is known, it exhibits the largest birefringence among the reported borates (0.439 at 546 nm), even over famous birefringent materials YVO 4 and TiO 2 . Meanwhile, it also owns a strong second harmonic generation (SHG) response of 2.4 times that of KH 2 PO 4 . Theoretical calculations display that its incredible optical properties mainly originate from the extremely intensive stereochemical activity lone pair (SCALP) of [SnO 7 Br 2 ] polyhedra, which results in the enhancement of birefringence and SHG response, increasing to 2.6‐ and 4.8‐fold, respectively, from Sn 2 B 5 O 9 Cl (SBOC) to SBOB. These perceptions will guide and accelerate the exploration of excellent birefringence and NLO materials in tin (II)‐based compound.