Stereochemically Active Tin(II)‐Induced Enhancement of Birefringence in Sn^IISn^IV(PO₄)₂ and SrSn(PO₄)PO₂(OH)₂

Abstract Two new tin(II) phosphates, Sn II Sn IV (PO 4 ) 2 and SrSn(PO 4 )PO 2 (OH) 2 , were synthesized by the high‐temperature solution method and hydrothermal method, respectively. Theoretical study indicates that by introducing tin(II) with stereochemical activity lone pairs (SCALP) in metal phosphates, the birefringence was enhanced, 0.048@1064 nm for Sn II Sn IV (PO 4 ) 2 and 0.080@1064 nm for SrSn(PO 4 )PO 2 (OH) 2 .