An Uncommon Hypervalent Fluorooxosilicophosphate

Abstract

The species diversity of silicon (including traditional tetrahedral coordinated silicon and hypervalent penta‐ and hexa‐coordinate silicon) gives rise to the structural richness and diverse properties of silicates. Among these silicon species, hypervalent silicon is very rare, not to mention almost unexplored mixed‐anion hypervalent fluoroxosilicate species. In this work, we successfully obtained a mixed‐anion fluorooxosilicophosphate Na4Si2PO4F9 consisting of two uncommon hypervalent fluoroxosilicate species, namely, trans‐SiO2F4 species and SiOF5 species. To the best of our knowledge, such hypervalent silicon species are reported for the first time in inorganic compounds. Remarkably, the coexistence of two distinct hypervalent fluoroxosilicate species in one compound is somewhat conflicted with Pauling's parsimony rule, but it indeed achieves an unlikely connection by PO4 and our phonon dispersion calculation confirms the structure stability of Na4Si2PO4F9. Temperature‐dependent conductivity measurements show that Na4Si2PO4F9 is a promising solid ionic conductor with a high conductivity of 4.0×10−5 S⋅cm−1 at 700 K and a low active energy of about 53.1 KJ⋅mol−1. This work will enrich the structure chemistry of silicates and may provide a new platform for solid ionic batteries.

Designing a Deep-UV Nonlinear Optical Fluorooxosilicophosphate

“…This work highlights fluorooxosilico­phosphate as a new inorganic compound, since compounds with either oxyfluoride SiO x F 4– x ( x = 1, 2, 3) tetrahedra or SiO x F 6– x ( x = 1, 2, 3, 4, 5) octahedra have been reported in only fluorinated organic compounds . Subsequently, our group discovered another fluorooxo­silico­phosphate, Na 4 Si 2 PO 4 F 9 , which contains two distinct hypervalent fluorooxosilicate units ( trans -SiO 2 F 4 and SiOF 5 ) . Unfortunately, both compounds crystallize in centrosymmetric space groups, as their locally asymmetric fluorooxosilico­phosphate moieties are aligned in opposite directions.…”

“…Clearly, the partial substitution of O by F decreases the local symmetry of SiO 5 F. Specifically, the Si–O bond lengths in the SiO 5 F polyhedra range from 1.757(9) to 1.788(7) Å, and the Si–F bond length is 1.660(6) Å (Table S3). , The SiP 2 O 10 F moieties are alternatingly linked with each other to generate zigzag chains of [SiP 2 O 7 F] ∞ via the 2 1 screw axis operation. The [SiP 2 O 7 F] ∞ chains are further linked to each other via −Si–O–P– linkages to form a corrugated [SiP 2 O 7 F] ∞ layer extending in the ab plane (Figure b).…”

Recent Development of Non-π-Conjugated Deep Ultraviolet Nonlinear Optical Materials

“…Partial substitution of fluorine for oxygen will produce new fluorine oxide fractions with reduced local symmetry, such as SiO x F 4– x ( x = 1, 2, 3) tetrahedra and SiO x F 6– x ( x = 1, 2, 3, 4, 5) octahedra. It is true that some metal silicate phosphate fluorides, such as K 4 Si 3 P 2 O 7 F 12 and Na 4 Si 2 PO 4 F 9 , have been identified, but their locally asymmetric fluoroxysilicate phosphate parts are arranged in opposite directions, and thus they all crystallize in centrosymmetric space groups.…”