New Bismuth Selenium Oxides: Syntheses, Structures, and Characterizations of Centrosymmetric Bi₂(SeO₃)₂(SeO₄) and Bi₂(TeO₃)₂(SeO₄) and Noncentrosymmetric Bi(SeO₃)(HSeO₃)

Three new mixed metal selenium oxides materials, Bi₂(SeO₃)₂(SeO₄), Bi₂(TeO₃)₂(SeO₄), and Bi­(SeO₃)­(HSeO₃), have been synthesized by hydrothermal and solid-state reactions using Bi­(NO₃)₃·5H₂O, SeO₂ (or TeO₂), H₂SeO₄, and Bi₂O₃ as reagents. The reported materials have been structurally characterized by single crystal X-ray diffraction. While Bi₂(SeO₃)₂(SeO₄) and Bi₂(TeO₃)₂(SeO₄) are crystallographically centrosymmetric (CS), Bi­(SeO₃)­(HSeO₃) crystallizes in a noncentrosymmetric (NCS) space group. The isostructural Bi₂(SeO₃)₂(SeO₄) and Bi₂(TeO₃)₂(SeO₄) exhibit three-dimensional framework structures that are composed of BiO₆, Se⁴⁺O₃ (or Te⁴⁺O₃), and Se⁶⁺O₄ polyhedra. However, Bi­(SeO₃)­(HSeO₃) exhibits corrugated layers that are composed of BiO₅, Se⁴⁺O₃, and Se⁴⁺O₂(OH) polyhedra. All three materials contain local asymmetric coordination environments attributable to the lone pairs on the Bi³⁺, Se⁴⁺, and/or Te⁴⁺ cations. Powder second-harmonic generation (SHG) measurements on NCS Bi­(SeO₃)­(HSeO₃) using 1064 nm radiation indicate that the material has a SHG efficiency of approximately 20 times that of α-SiO₂ and is not phase-matchable (type 1). The origin and magnitude of the SHG efficiency of Bi­(SeO₃)­(HSeO₃) is explained by determining the net direction of the polarizations arising from individual asymmetric polyhedra. Infrared spectroscopy, thermal analysis, elemental analysis, and dipole moment calculations for the reported materials are also presented.