Synthesis and Characterization of the Lithium-Rich Phosphidosilicates Li₁₀Si₂P₆ and Li₃Si₃P₇

Abstract

The lithium phosphidosilicates LiSiP and LiSiP are obtained by high-temperature reactions of the elements or including binary Li-P precursors. LiSiP (P2/n, Z = 2, a = 7.2051(4) Å, b = 6.5808(4) Å, c = 11.6405(7) Å, β = 90.580(4)°) features edge-sharing SiP double tetrahedra forming [SiP] units with a crystal structure isotypic to NaSiP and NaGeP. LiSiP (P2/m, Z = 2, a = 6.3356(4) Å, b = 7.2198(4) Å, c = 10.6176(6) Å, β = 102.941(6)°) crystallizes in a new structure type, wherein SiP tetrahedra are linked via common vertices and which are further connected by polyphosphide chains to form unique [SiP] double layers. The two-dimensional Si-P slabs that are separated by Li atoms can be regarded as three covalently linked atoms layers: a defect α-arsenic type layer of P atoms sandwiched between two defect wurzite-type SiP layers. The single crystal and powder X-ray structure solutions are supported by solid-state Li,Si, and P magic-angle spinning NMR measurements.

Fast Lithium Ion Conduction in Lithium Phosphidoaluminates

“…Theh igh structural diversity of the Li atoms including disorder and split positions reflects the possibility of high lithium ion mobility.L i-P distances in the tetrahedral voids range from 2.50(1) to 2.73(1) ,a nd in the octahedral voids they range from 2.56(1) to 3.46 (1) .T he bond lengths are similar to those in other ternary phases containing Li and P, such as Li 8 SiP 4 ,Li 2 SiP 2 ,L i 10 SiP 2 ,a nd Li 3 Si 3 P 7 . [47,60] According to the valence rules,L i 9 AlP 4 is an electronprecise compound and can be described as (Li + ) 9 [AlP 4 ] 9À , with formally two negative charges for the Pa toms and one negative charge for the Al atom, balanced by nine Li + ions.…”

Synthesis, Crystal Structure, and Chemical Bonding of Ba2SiP4

“…The spinning sidebands of the 31 P spectrum cover a range of about 200 ppm, which indicates a fairly large anisotropy of the chemical shift tensor, as expected for the Si-P-P-Si motive. [14] Ba 2 SiP 4 crystallizes in a new structure type with slightly distorted SiP 4 -tetrahedra [d(Si-P) = 223.45 (8) pm] which are exclusively connected via homonuclear P-P bonds [d(P-P) = 221.01 (15) pm] to form a three-dimensional network with barium atoms in the lacunae (Figure 3). The coordination polyhedra may be described as a pentagonal bipyramid, where one vertex is a P 2 dimer (Figure 4).…”

“…Examples for phosphidosilicates with P-P bonds are LaSi 2 P 6 [10] which contains not less than four different polyphosphide units (P n ) (n+2)-with n = 3-6, or the recently published Li 3 Si 3 P 7 with polyphosphide chains. [14] P 2 dimers were found in AlSiP 3 [15] or Ca 3 Si 8 P 14 [16] with P-P distances around 220 pm as typical for single bonds.…”

Polymorphism of Ba2SiP4

“…More common are SiP 4 anions with reduced charge density achieved by different condensation degrees leading to chains, layers, or three‐dimensional network motifs. A 10 Si 2 P 6 ( A = Li, Na) exhibits edge‐shared [Si 2 P 6 ] 10– entities whereas the charge density is decreased furthermore by edge condensation of these units to infinite [SiP 2 ] 2– chains found in K 2 SiP 2 . Interestingly, to date layered phosphidosilicates were only observed with supertetrahedral entities constituted of vertex sharing SiP 4 tetrahedra in CaSiP 2 and KSi 2 P 3 .…”

“…The possibility of the formation of homonuclear phosphorus bonding distinguishes the family of phosphidosilicates from the oxido‐ and nitridosilicates. Isolated P–P bonding was described in AlSiP 3 , Ca 3 Si 8 P 14 , Ba 2 Si 3 P 6 and Ba 4 Si 3 P 8 , for example, whereas in LaSi 2 P 6 up to four different polyphosphide anions (P n ) –( n +2) with n = 3–6 and in Li 3 Si 3 P 7 [4a] polyphosphide chains exist. Tetragonal Ba 2 SiP 4 ‐ tI 28 is the first example where all SiP 4 tetrahedra are connected by P–P bonds.…”