From Pb 6 (HPO 3 )(H 2 PO 3 )Cl 9 to Pb 6 (HPO 3 ) 2 Br 8 (H 2 O)·H 2 O: Halogen Regulation to Achieve Inorganic Metal Phosphite Halide Nonlinear Optical Material with Unprecedented Pb-Centered Polyhedral Units.

Nonlinear optical (NLO) crystals are widely used in various fields. The introduction of lone-pair cations is regarded as an effective strategy to explore NLO crystals. In this work, two novel lead phosphite halides, centrosymmetric Pb 6 (HPO 3 )(H 2 PO 3 )Cl 9 and noncentrosymmetric Pb 6 (HPO 3 ) 2 Br 8 (H 2 O)·H 2 O, were obtained via a hydrothermal method. Pb 6 (HPO 3 )(H 2 PO 3 )Cl 9 is the first reported lone-pair metal phosphite with two kinds of phosphite groups (HPO 3 2- and H 2 PO 3 - ) and Pb 6 (HPO 3 ) 2 Br 8 (H 2 O)·H 2 O is the first inorganic NLO phosphite halide with a phase-matchable SHG effect of 1.02 × KDP. In addition, the Pb-centered polyhedral units of PbOCl 4 , PbOCl 6 , PbO 2 Cl 5 , PbO 2 Br 5 , PbOBr 6 , and PbO 3 (H 2 O)Br 3 in these two structures have never been reported before. An in-depth study on the structure-property relationship of the two compounds with halogen substitution is also performed.