Pb2Cl2(HPO3)(H2O) and Pb3Br2(HPO3)2: Two Phosphite Halides with 3D Structural Networks and Enlarged Birefringence.

Abstract

Compounds constructed by mixed anions are widely favorable for their diverse crystal structures and physical performances. Here, two lead phosphite halides, Pb2Cl2(HPO3)(H2O) (1) and Pb3Br2(HPO3)2 (2), were obtained by facile hydrothermal reactions. Both compounds crystallize in the space group Pnma. 1 exhibits a 3D structure composed of HPO3 units, PbCl4O3 pentagonal bipyramids, and PbO3 pyramids. 2 also shows a 3D framework built by HPO3 units, PbO2Br4 octahedron, PbO5 and PbO3Br2 square pyramids. By introducing halogen anions to the lead phosphite system, 1 and 2 show enhanced birefringences of 0.083 and 0.072 at 1064 nm, respectively, compared with 0.023@1064 nm for Pb2(HPO3)2. In this work, syntheses, crystal structures, optical properties, and theoretical calculation results have been studied in detail.