Noncentrosymmetric versus Centrosymmetric: Halogen Induced Variable Coordination Modes of Sn 2+ and Structural Transition in Sn 3 B 3 O 7 X (X = Cl and Br).

Two new borate halides, SnBOX (X = Cl and Br), were successfully synthesized via introducing Sn with lone-pair and halogen into borate. Interestingly, halogen-induced variable coordination modes of Sn and anion frameworks make them crystallize in different space groups, from noncentrosymmetric (2) to centrosymmetric (). SnBOCl possesses an SHG response of about 0.5 times that of KDP, while SnBOBr exhibits a large birefringence (0.123@1064 nm). The theoretical calculations were performed to elucidate the structure-property relationships.