Pb 2 Cl 2 (HPO 3 )(H 2 O) and Pb 3 Br 2 (HPO 3 ) 2 : Two Phosphite Halides with 3D Structural Networks and Enlarged Birefringence.

Compounds constructed by mixed anions are widely favorable for their diverse crystal structures and physical performances. Here, two lead phosphite halides, Pb 2 Cl 2 (HPO 3 )(H 2 O) ( 1 ) and Pb 3 Br 2 (HPO 3 ) 2 ( 2 ), were obtained by facile hydrothermal reactions. Both compounds crystallize in the space group Pnma . 1 exhibits a 3D structure composed of HPO 3 units, PbCl 4 O 3 pentagonal bipyramids, and PbO 3 pyramids. 2 also shows a 3D framework built by HPO 3 units, PbO 2 Br 4 octahedron, PbO 5 and PbO 3 Br 2 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 Pb 2 (HPO 3 ) 2 . In this work, syntheses, crystal structures, optical properties, and theoretical calculation results have been studied in detail.