[Pb(ptz)(OH)(H₂O)]: A Hybrid Nonlinear Optical Crystal with Large Birefringence

The development of nonlinear optical (NLO) crystals remains crucial for solid-state laser applications. In this work, a chiral lead(II)-based hybrid material, [Pb(ptz)(OH)(H₂O)] (Hptz = 5-(2-pyrazinyl)-1H-tetrazole), was synthesized, exhibiting a one-dimensional chain structure assembled through stereochemically active lone pair (SCALP) Pb²⁺ cations, OH^-, and electronically asymmetric π-conjugated ptz^- ligands. The combined influence of asymmetric π-conjugated organic ligands and SCALP-containing metal centers promotes noncentrosymmetric (NCS) crystal formation, yielding measurable optical properties, including 0.7 times KH₂PO₄ (KDP) second-harmonic generation (SHG) efficiency, substantial birefringence (Δn = 0.076 at 546 nm), and a 3.45 eV optical band gap. Structural characterization and computational studies attribute these optical characteristics to cooperative effects between distorted [PbO₃N₂] polyhedra and aligned ptz^- units, demonstrating that a strategic combination of SCALP metal cations with asymmetric π-conjugated organic ligands provides an effective pathway for designing hybrid linear/NLO materials.