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, Sn 3 B 3 O 7 X (X = Cl and Br), were successfully synthesized via introducing Sn 2+ with lone-pair and halogen into borate. Interestingly, halogen-induced variable coordination modes of Sn 2+ and anion frameworks make them crystallize in different space groups, from noncentrosymmetric ( Pna 2 1 ) to centrosymmetric ( Pbca ). Sn 3 B 3 O 7 Cl possesses an SHG response of about 0.5 times that of KDP, while Sn 3 B 3 O 7 Br exhibits a large birefringence (0.123@1064 nm). The theoretical calculations were performed to elucidate the structure-property relationships.