Synthesis, crystal structures and properties of lead phosphite compounds

Here, we report the preparation and characterization of two lead(II) phosphites, namely, Pb₂(HPO₃)₂ and Pb₂(HPO₃)(NO₃)₂ through hydrothermal reaction or simple solution synthesis, respectively. A new lead phosphite, namely, Pb₂(HPO₃)₂, crystallizes in the noncentrosymmetric space group Cmc2₁ (no. 36), which features 3D framework formed by the interconnection of 2D layer of lead(II) phosphites and 1D chain of [Pb(HPO₃)₅]_∞. The nonlinear optical properties of Pb₂(HPO₃)(NO₃)₂ have been studied for the first time. The synergistic effect of the stereo-active lone-pairs on Pb²⁺ cations and π-conjugated NO₃ units in Pb₂(HPO₃)(NO₃)₂ produces a moderate second harmonic generation (SHG) response of ∼1.8×KDP (KH₂PO₄), which is phase matchable (type I). IR, UV–vis spectra and thermogravimetric analysis (TGA) for the two compounds were also measured. - Graphical abstract: Two lead phosphites Pb₂(HPO₃)₂ and Pb₂(HPO₃)(NO₃)₂ are studied. A new lead phosphite Pb₂(HPO₃)₂ features a unique 3D framework structure and Pb₂(HPO₃)(NO₃)₂ shows a moderate SHG response of ∼1.8×KDP (KH₂PO₄). - Highlights: • A new lead phosphite, Pb₂(HPO₃)₂ is reported. • Pb₂(HPO₃)₂ features a unique 3D framework structure. • NLO property of Pb₂(HPO₃)(NO₃)₂ is investigated. • Pb₂(HPO₃)(NO₃)₂ produces a moderate SHG response of ∼1.8×KDP (KH₂PO₄).