First chiral fluorinated lead vanadate selenite Pb₂(V₂O₄F)(VO₂)(SeO₃)₃with five asymmetric motifs and large optical properties

The first fluorinated lead vanadate selenite Pb₂(V₂O₄F)(VO₂)(SeO₃)₃(PVOFS) was successfully synthesizedviaa mild hydrothermal method. This compound crystallizes in the chiral space groupP2₁2₁2₁of the orthorhombic system and it is the first noncentrosymmetric structure in the Pb^II-V^V-Se^IV-O-F system. PVOFS is composed of five kinds of second-order Jahn-Teller susceptible asymmetric motifs, including three distinct types of vanadium-centered polyhedral units ([VO₅F], [VO₆] and [VO₅]), [SeO₃] pyramids and Pb²⁺cations. It features a unique three-dimensional open framework structure displaying three types of tunnels (10-, 8- and 7-membered rings), which enriches the structural diversity for fluorinated vanadate selenite systems. Optical property studies revealed that PVOFS shows a second-harmonic generation response of 0.3 times that of the commercial KH₂PO₄with phase matching behavior, a wide transparent region covering IR windows, an optical band gap of 2.35 eV, a high laser damage threshold of 61 times that of AgGaS₂, and a large birefringence of 0.105 at 1064 nm. Theoretical calculations have been performed to clarify the correlation between the molecular structure and the optical properties of PVOFS.