# Phosphidosilicates

The phosphidosilicates or phosphosilicides are inorganic compounds containing silicon bonded to phosphorus and one or more other kinds of elements. In the phosphosilicates each silicon atom is surrounded by four phosphorus atoms in a tetrahedron. The triphosphosilicates have a SiP$_3$ unit, that can be a planar triangle like carbonate CO$_3$. The phosphorus atoms can be shared to form different patterns e.g. [Si$_2$P$_6$]$^{10−}$ which forms pairs, and [Si$_3$P$_7$]$^{3−}$ which contains two-dimensional double layer sheets. [SiP$_4$]$^{8−}$ with isolated tetrahedra, and [SiP$_2$]$^{2−}$ with a three dimensional network with shared tetrahedron corners. SiP clusters can be joined, not only by sharing a P atom, but also by way of a P-P bond. This does not happen with nitridosilicates or plain silicates.
The phosphidosilicates can be considered as a subclass of the pnictogenidosilicates, where P can be substituted by N (nitridosilicates), As, or Sb. Also Silicon can be substituted to form other series of compounds by replacement with other +4 oxidation state atoms like germanium, tin, titanium or even tantalum.

## List

| formula | name | crystal system | space group | unit cell Å | form | MW | density | properties |
| Li$_2$SiP$_2$ | | tetragonal | I4$_1$/acd | a=12.111 Å, c=18.658 Å, Z=32 V=2732.6 | 4 SiP$_4$ tetrahedra are linked together to form a supertetrahedron. Supertetrahedrons are linked together by corner sharing. | 103.91 | 2.02 | |
| LiSi$_2$P$_3$ | | | I4$_1$/a | a=18.4757 Å, c=35.0982 Å, Z=100 | Interpenetrating networks of bridged supertetrahedra | | | |
| Li$_3$Si$_3$P$_7$ | | monoclinic | P2$_1$/m | a = 6.3356 Å, b = 7.2198 Å, c = 10.6176 Å, β = 102.941°, Z = 2 | | | | grey |
| Li$_5$SiP$_3$ | | Cubic | Fm3m | a=5.84 Z=1.33 | SiP$_4$ tetrahedra, but some Si replace by Li | | | |
| Li$_{10}$Si$_2$P$_6$ | | | P2$_1$/n | a = 7.2051 Å, b = 6.5808 Å, c = 11.6405 Å, β = 90.580°, Z = 4 | contains Si$_2$P$_6$ units with two Si atoms linked by two P atoms | | | also known by Li$_5$SiP$_3$ |
| Li$_8$SiP$_4$ | lithium orthophosphidosilicate | cubic | Pa3 | a=11.6784 Z=8 V=1592.76 | | 207.49 | 1.73 | orange red |
| Li$_{14}$SiP$_6$ | | Cubic | Fm3m | a=5.9393 Z=4 | SiP$_4$ tetrahedra, but some Si replace by Li | | 1.644 | |
| Na$_{19}$Si$_{13}$P$_{25}$ | | triclinic | P1 | a =13.3550 Å, b =15.3909 Å, c =15.4609 Å, α =118.05°, β =111.71°, γ =93.05°, Z =2 | T3 supertetrahedra | | | sodium ion conductor |
| Na$_{23}$Si$_{19}$P$_{33}$ | | monoclinic | C2/c | a =28.4985 Å, b =16.3175 Å, c = 13.8732 Å, β =102.35°, Z =4 | solely T3 supertetrahedra | | | sodium ion conductor |
| Na$_{23}$Si$_{28}$P$_{45}$ | | monoclinic | P2$_1$/c | a =19.1630 Å, b =23.4038 Å, c = 19.0220 Å, β =104.30°, Z =4 | T3 and T4 supertetrahedra | | | sodium ion conductor |
| Na$_{23}$Si$_{37}$P$_{57}$ | | monoclinic | C2/c | a =34.1017 Å, b =16.5140 Å, c = 19.5764 Å, β =111.53°, Z =4 | solely T4 supertetrahedra | | | sodium ion conductor |
| LT-NaSi$_2$P$_3$ | | tetragonal | I4$_1$/a | a =19.5431 Å, c = 34.5317 Å, Z =100 | fused T4 and T5 supertetrahedra | | | sodium ion conductor |
| HT-NaSi$_2$P$_3$ | | tetragonal | I4$_1$/acd | a =20.8976 Å, c = 40.081 Å, Z =128 | solely fused T5 supertetrahedra | | | sodium ion conductor |
| Na$_2$SiP$_2$ | disodium diphosphidosilicate | Tetrahedral | Pccn | a = 12.7929 Å, b = 22.3109 Å, c = 6.0522 Å and Z = 16 | edge‐shared SiP$_4$ tetrahedra with 1 width chains | | | dark red 0.43 eV |
| Na$_5$SiP$_3$ | | monoclinic | P2$_1$/c | Z=4 a= 7.352 Å, b= 7.957, Å c= 13.164 Å, α=90.757° | | | 2.06 | also known by Na$_{10}$Si$_2$P$_6$ band gap 1.292 eV |
| Na$_3$K$_2$SiP$_3$ | trisodium dipotassium triphosphidosilicate | Orthorhombic | Pnma | a=14.580 b=4.750 c= 13.020 V=901.7 Z=4 | SiP$_3$ triangles | | | |
| Na$_4$Ca$_2$SiP$_4$ | | hexagonal | P6$_3$mc | a=913 c=617 V=151.5 | SiP$_4$ tetrahedra | | 2.128 | |
| Na$_4$Sr$_2$SiP$_4$ | | hexagonal | P6$_3$mc | a=9.283 c=7.295 V=164 | | | 2.498 | |
| Na$_4$Eu$_2$SiP$_4$ | | hexagonal | P6$_3$mc | a=9.251 c=7.198 V=160.7 | | | 3.226 | |
| MgSiP$_2$ | | tetragonal | I42d | a=5.721 c=10.095 | | | | orange yellow; semiconductor band gap 2.24 eV; decomposed by water or acid |
| AlSiP$_3$ | | orthorhombic | Pmnb | a = 9.872, b = 5.861, c = 6.088, Z=4 | P-P bonds | | | black |
| K$_2$SiP$_2$ | | orthorhombic | Ibam | a = 12.926, b = 6.867, c= 6.107, Z=4, V=542.07 | one dimensional chain | | 2.061 | |
| KSi$_2$P$_3$ | | monoclinic | C2/c | a=10.1327 Å, b=10.1382 Å, c=21.118 Å, β=96.88°, Z=8 V=2153.8Å$^3$ | solely fused T3 supertetrahedra | | 2.321 | dark red, band gap 1.72 eV |
| KSi$_2$P$_3$ | | tetragonal | I4$_1$/acd | a =21.922 Å, c = 39.868 Å, Z =128 | solely fused T5 supertetrahedra | | | potassium ion conductor |
| Ca$_2$Si$_2$P$_4$ | | | P4$_1$2$_1$2 | a = 7.173, c = 26.295 | | | | band gap 0.984 eV |
| Ca$_3$Si$_2$P$_4$ | | monoclinic | | a = 7.073 Å, b = 17.210 Å, c = 6.918 Å, β = 111.791° | | | | band gap 0.826 eV |
| Ca$_3$Si$_8$P$_{14}$ | | monoclinic | P2$_1$/c | a = 12.138 Å, b = 13.476 Å, c = 6.2176 Å, β = 90.934° | | | | band gap 0.829 eV |
| Ca$_4$SiP$_4$ | | cubic | | a=11.875 V=1675 | | | 2.48 | |
| MnSiP$_2$ | | tetrahedral | I 4 2 d | a 5.5823 c 10.230 | | | | metallic; SHG 32.8 pm/V |
| Fe$_5$SiP | | | | a=6.766 c=12.456 V=493.8 Z=6 | | | 6.83 | |
| CoSi$_3$P$_3$ | | monoclinic | P2$_1$ | (pseudo orthrhombic) a = 5.899, b = 5.703, c = 12.736, β = 90.00° Z=4 | | | | resistivity 0.62 Ohm cm band gap 0.12 eV |
| NiSi$_3$P$_4$ | | tetragonal | I42m | a = 5.1598 c =10.350 Z = 2 | | | 3.22 | |
| NiSi$_2$P$_3$ | | | Imm2 | a = 3.505, b = 11.071, c = 5.307, Z = 2 | | | | |
| FeSi$_4$P$_4$ | | | | a = 4.876, b = 5.545, c = 6.064, α = 85.33°, β = 68.40°, γ = 70.43° Z=4 P and Si random | | | 3.38 | resistivity 0.3 Ohm cm band gap 0.15, can take in Li or Na |
| Cu$_4$SiP$_8$ | | | I4$_1$/a | a = 12.186, c = 5.732, Z = 8 | P-P bonds | | | |
| ZnSiP$_2$ | | Tetragonal | I42d | a = 5.399 Å c = 10.435 Å Z=4 V=304.173 Å$^3$ | chalcopyrite structure SiP$_4$ and Zn$_4$ tetrahedra | 154.936 | 3.3 (measured) | dark red clear; red luminescent; semiconductor; band gap 2.01 eV |
| ZnSiP$_2$ | | Cubic | | | | | | over 27 GPa Superconductor T$_c$ = 8.2K |
| Sr$_2$SiP$_4$ | | | | | | | | band gap 1.41 eV |
| Sr$_4$SiP$_4$ | | cubic | | a=12.426 V=1919 | | | 3.48 | |
| SrSi$_7$P$_{10}$ | | triclinic | P1 | a =6.1521 Å, b =8.0420 Å, c =8.1374 Å, α =106.854°, β =99.020°, γ =105.190°, Z =1 | tetrahedral network derived from T2 supertetrahedra | | | band gap 1.1 eV |
| Mg$_2$Sr$_3$Si$_{20}$P$_{30}$ | | hexagonal | P6$_3$ | a = 15.7767 c = 11.7407 | | | | |
| MgSr$_3$Si$_3$P$_7$ | | | P31m | a = 18.7339 c = 6.1393 | | | | |
| RhSi$_3$P$_3$ | | monoclinic | C2 | a=5.525, b=7.210, c=5.522 β=118.31°, Z=2 P and Si random | | | 4.005 | black |
| RuSi$_4$P$_4$ | | triclinic | P1 | a = 4.936, b = 5.634, c = 6.162, α = 85.51°, β = 68.26°, γ = 70.69° Z=1 V=150 | | | 3.74 | metallic |
| RuSi$_4$P$_4$ | | triclinic | P1 | a=4.9362 b=5.6326 c=6.1649 α=85.5073° β=68.2559° γ=70.6990° | | | 3.732 | dark red;band gap 1.9 eV |
| AgSiP$_2$ | | Tetragonal | I42d | 6.5275, c = 8.550, Z = 4; V = 364.3 | SiP$_4$ corner sharing | 305.77 | 5.58 | shiny black |
| Mg$_2$In$_3$Si$_2$P$_7$ | | monoclinic | P2$_1$ | a 6.9375 b 6.5646 c 14.469 β 103.87° Z=2 | | 639.7 | 3.458 | SHG 7.1 × AgGaS$_2$; band gap 2.21 |
| Sn$_{4.2}$Si$_9$P$_{16}$ | | rhombohedral | R3 | a = 9.504 Å, α = 111.00°, and Z = 1 | | | | band gap 0.2 |
| CdSiP$_2$ | | tetragonal | I42d | a = 5.680 c = 10.431 Å Z=4 V=336.494 Å$^3$ | chalcopyrite structure | 202.434 | 3.995 | carmine colour; red luminescent |
| Cs$_2$SiP$_2$ | Dicesium catena-diphosphidosilicate | Orthorhombic | Ibam | | | | | |
| Cs$_5$SiP$_3$ | Pentacesium triphosphidosilicate | Orthorhombic | Pnma | a=6.064, b=14.336, c=15.722 | SiP$_3$ planar triangles | | | dark metallic, air sensitive |
| BaSi$_7$P$_{10}$ | | triclinic | P1 | a =6.1537 Å, b =8.0423 Å, c =8.1401 Å, α =106.863°, β =99.050°, γ =105.188°, Z =1 | tetrahedral network derived from T2 supertetrahedra | | | |
| Ba$_2$SiP$_4$ | | Tetragonal | I42d | a = 9.90.57 Å, c = 7.31.80 Å; Z = 4 V=718.06 Å | contains P-P bonds | 426.65 | | band gap 1.45 eV |
| Ba$_2$SiP$_4$ | | Orthorhombic | Pnma | a=12.3710 b=4.6296 c=7.9783 Z= 8 V=1443.9 | chains of Si-P-Si | 426.65 | 3.925 | black band gap 1.7 eV |
| Ba$_2$Si$_3$P$_6$ | | | | | | | | band gap 1.88 |
| Ba$_3$Si$_4$P$_6$ | | monoclinic | P2$_1$/m | a=1153.7 Å, b=728.1 Å, c=752.7 Å, β = 99.41° V=623.76 Z=2 | Zintl compound P-P and Si-Si bonds | | 3.78 | black metallic |
| Ba$_4$SiP$_4$ | | cubic | | a=13.023 V=2219 | | | 4.22 | |
| BaCuSi$_2$P$_3$ | | monoclinic | | a=4.5659 b=10.1726 c=6.8236 β = 109.311 V=299.10 | layered | | | |
| LaSiP$_3$ | | monoclinic | | a = 5.972, b = 25.255, c = 4.168, β= 135.71°, Z = 4 | two dimensional network of boat-shaped six-membered rings of Si-P-Si-P-Si-P | | | |
| LaSi$_2$P$_6$ | | | Cmc2$_1$ | a=10.129 b=28.17 c=10.374 Z=16 | P-P bonds | 380.9 | 3.42 | grey |
| La$_2$Mg$_3$SiP$_6$ | | orthorhombic | Pnma | a=11.421 b=8.213 c=10.677 Z=4 | | | | |
| CeSiP$_3$ | | orthorhombic | Pn21a | a = 5.861, b= 5.712, c= 25.295 V=846.7 Å$^3$, Z=8 | P-P bonds | 261.13 | 4.095 | |
| CeSi$_2$P$_6$ | | | Cmc21 | a= 10.118 b= 28.03 c= 10.311 Z= 16, V=2.924 | P-P bonds | 382.1 | 3.47 | grey |
| Ce$_2$Mg$_3$SiP$_6$ | | orthorhombic | Pnma | a=11.356 b=8.188 c=10.564 Z=4 | | | | |
| PrSi$_2$P$_6$ | | | Cmc21 | a= 10.085 b= 27.95 c= 10.267 Z= 16, V=2.895 nm$^3$ | P-P bonds | | | grey |
| NdSi$_2$P$_6$ | | | Cmc21 | a= 10.031,b= 27.81,c= 10.245,Z= 16, V=2.857 | P-P bonds | | | grey |
| ReSi$_4$P$_4$ | | | | | | | | |
| OsSi$_4$P$_4$ | | triclinic | P1 | a = 4.948, b = 5.620, c = 6.175, α = 85.65, β = 68.36, γ = 70.89, Z=4 V=150.6 | | | 4.72 | metallic |
| IrSi$_3$P$_3$ | | monoclinic | C2 | a=6.577, b=7.229, c=5.484 β=117.91°, Z=2 | | | | black |
| IrSi$_3$P$_3$ | | monoclinic | Cm | a=6.5895 b=7.2470 c=5.4916 β=117.892 | | | | dark red;band gap 1.8 eV |
| PtSi$_2$P$_2$ | | monoclinic | P2$_1$ | a=6.025 Å, b=9.468 Å, c=11.913 Å, β=102.91°,Z=8, V=552.2 | | | 6.327 | high resistance metallic,shiny black, air sensitive |
| PtSi$_3$P$_2$ | | triclinic | P1 | a=4.840 Å,b=5.482 Å,c=8.052 Å, α=91.57°, β=93.52°, γ=108.14°, Z=2 V=202.3 | | | 5.656 | shiny black |
| AuSiP | | rhombohedral | R3m | a=3.459, c = 17.200, Z = 3; V = 178.19 | | 256.03 | 7.16 | shiny black |
| Th$_2$SiP$_5$ | | triclinic | | a=4.04.3 Å, b=4.04.5 Å, c = 10.279 pm, α = 90.09°, β = 90.09° and γ = 89.50°, Z = 1 | chains of corner linked SiP$_4$ tetrahedra, and square net of P | | | |