Tetrasulfur tetranitride
| Tetrasulfur tetranitride | |
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| Identifiers | |
| CAS number | 28950-34-7  |
| PubChem | 141455 |
| ChemSpider | 124788 |
| Jmol-3D images | Image 1 Image 2 |
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| Properties | |
| Molecular formula | N4S4 |
| Molar mass | 184.287 g mol−1 |
| Appearance | Vivid orange, opaque crystals |
| Melting point |
187 °C, 460 K, 369 °F |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Tetrasulfur tetranitride is an inorganic compound with the formula S4N4. This gold-poppy coloured solid is the most important binary sulfur nitride, which are compounds that contain only the elements sulfur and nitrogen. It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding.[1][2]
Nitrogen and sulfur have similar electronegativities. When atoms are so evenly matched, they often form extensive families of covalently bonded structures. Indeed, a large number of S-N and S-NH compounds are known with S4N4 as their parent.
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Structure [edit]
S4N4 adopts an unusual “extreme cradle” structure, with D2d point group symmetry. It can be viewed as a derivative of a hypothetical eight-membered ring of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are separated by 2.586 Å, resulting in a cage-like structure as determined by single crystal X-Ray diffraction.[3] The nature of the "transannular" S–S interactions remains a matter of investigation because it is significantly shorter than the sum of the van der Waal's distances[4] but has been explained in the context of molecular orbital theory.[1] The bonding in S4N4 is considered to be delocalized, which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are almost the same.
Properties [edit]
S4N4 is stable to air. It is, however, unstable in the thermodynamic sense with a positive enthalpy of formation of +460 kJ mol−1. This endothermic enthalpy of formation anticipates its inherent instability, and originates in the difference in energy of S4N4 compared to its highly stable decomposition products:
- 2 S4N4 → 4 N2 + S8
Although many complex molecules are unstable in a thermodynamic sense yet stable kinetically, this is uncommon for very simple compositions, such as sulfur nitride.
Because one of its decomposition products is a gas, S4N4 is an explosive.[1] Purer samples tend to be more explosive. Small samples can be detonated by striking with a hammer.
S4N4 is thermochromic, changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C.[1]
Synthesis [edit]
S4N4 was first prepared in 1835 by W. Gregory, by the reaction of sulfur monochloride with ammonia.[5]
Until recently, S4N4 was prepared by the reaction of ammonia with SCl2 in carbon tetrachloride followed by extraction into dioxane, producing sulfur and ammonium chloride as side-products:[6]
- 24 SCl2 + 64 NH3 → 4 S4N4 + S8 + 48 NH4Cl
A related synthesis employs sulfur monochloride and NH4Cl instead:[1]
- 4 NH4Cl + 6 S2Cl2 → S4N4 + 16 HCl + S8
A more recent synthesis entails the use of [(Me3Si)2N]2S as a precursor with pre-formed S–N bonds. [(Me3Si)2N]2S is prepared by the reaction of lithium bis(trimethylsilyl)amide and SCl2.
- 2 [(CH3)3Si]2NLi + SCl2 → [((CH3)3Si)2N]2S + 2 LiCl
The [((CH3)3Si)2N]2S reacts with the combination of SCl2 and SO2Cl2 to form S4N4, trimethylsilyl chloride, and sulfur dioxide:[7]
- [((CH3)3Si)2N]2S + SCl2 + SO2Cl2 → S4N4 + 4 (CH3)3SiCl + SO2
Acid-base reactions [edit]
S4N4 serves as a Lewis base by binding through nitrogen to strongly Lewis acidic compounds such as SbCl5 and SO3. The cage is distorted in these adducts, thus delocalization of electrons may be disrupted.[1]
- S4N4 + SbCl5 → S4N4·SbCl5
- S4N4 + SO3 → S4N4·SO3
The reaction of [Pt2Cl4(PMe2Ph)2] with S4N4 is reported to form a complex where a sulfur forms a dative bond to the metal. This compound upon standing is isomerised to a complex in which a nitrogen atom forms the additional bond to the metal centre.
It is protonated by HBF4 to form a tetrafluoroborate salt:
- S4N4 + HBF4 → [S4N4H+][BF−
4]
The soft Lewis acid CuCl forms a polymer containing intact S4N4 rings as the bridging ligands:[1]
- n S4N4 + n CuCl → (S4N4)n-μ-(-Cu-Cl-)n
S4N4 is sensitive to hydrolysis in the presence of base. Dilute NaOH hydrolyzes S4N4 as follows, yielding thiosulfate and trithionate:[1]
- 2 S4N4 + 6 OH− + 9 H2O → S2O2−
3 + 2 S3O2−
6 + 8 NH3
More concentrated base yields sulfite:
- S4N4 + 6 OH− + 3 H2O → S2O2−
3 + 2 SO2−
3 + 4 NH3
Reactions with metal complexes [edit]
This area has been reviewed.[2][8]
Reactions of S4N4 where the ring remains intact [edit]
S4N4 reacts with Vaska's complex ([Ir(Cl)(CO)(PPh3)2] in an oxidative addition reaction to form a six coordinate iridium complex where the S4N4 binds through two sulfur atoms and one nitrogen atom. This compound arises by the formal breaking of one S-N bond in the oxidative addition, followed by the coordination of the lone pair on another sulfur atom to form a dative bond. A related Pt(IV) compound arises from Zeise's salt.
Reactions of S4N4 where the ring does not remain intact [edit]
The reaction of S4N4 with the [Pd2Cl6]2− anion forms a series of three palladium complexes in which the S4N4 ring has been fragmented.
S4N4 as a precursor to other S-N compounds [edit]
Many important S-N compounds are prepared from S4N4.[9] Reaction with piperidine generates [S4N5]−:
- 3 S4N4 + 4 C5H10NH → (C5H10NH2)+[S4N5]− + (C5H10N)2S + ⅜ S8 + N2
It is indicative of the richness of this area that a related cation is also known, i.e. [S4N5]+.
Treatment with tetramethylammonium azide produces the heterocycle [S3N3]−:
- S4N4 + NMe4N3 → NMe4[S3N3] + ⅛ S8 + 2 N2
In the language of electron counting, [S3N3]− has 10 pi-electrons: 2e−/S plus 1e−/N plus 1e− for the negative charge.
In an apparently related reaction, the use of PPN+N3 gives a salt containing the blue [NS4]− anion:[10]
- 2 S4N4 + PPN(N3) → PPN[NS4] + ½ S8 + 5 N2
The anion NS4− has a chain structure described using the resonance [S=S=N-S-S]− ↔ [S–S–N=S=S]−.
Reaction with alkynes [edit]
S4N4 reacts with electron-poor alkynes.[11]
Polythiazyl [edit]
Passing gaseous S4N4 over silver metal yields the low temperature superconductor polythiazyl or polysulfurnitride (transition temperature (0.26±0.03) K[12]), often simply called "(SN)x". In the conversion, the silver first becomes sulfided, and the resulting Ag2S catalyzes the conversion of the S4N4 into the four-membered ring S2N2, which readily polymerizes.[1]
- S4N4 + 8 Ag → 4 Ag2S + 2 N2
- S4N4 → (SN)x
Miscellaneous facts [edit]
S4N4 has been shown to co-crystallize with benzene and the C60 molecule.[13]
Se4N4 [edit]
The selenium compound Se4N4 is known and has been the subject of some research.[14][15] In addition, adducts of aluminium chloride with Se2N2 have been isolated; this is formed from Se4N4.[16]
Safety [edit]
S4N4 is shock-sensitive, thus grinding solid samples should be avoided. Purer samples are reportedly more sensitive than those contaminated with elemental sulfur.
References [edit]
- ^ a b c d e f g h i Greenwood, N. N.; Earnshaw, A. (1997). Chemical Elements (2nd ed.). Boston, MA: Butterworth-Heinemann. pp. 721–725.
- ^ a b Chivers, T. (2004). A Guide To Chalcogen-Nitrogen Chemistry. Singapore: World Scientific Publishing. ISBN 981-256-095-5.
- ^ Sharma, B. D.; Donohue, J. (1963). "The Crystal and Molecular Structure of Sulfur Nitride, S4N4". Acta Crystallographica 16 (9): 891–897. doi:10.1107/S0365110X63002401.
- ^ Rzepa, H. S.; Woollins, J. D. (1990). "A PM3 SCF-MO Study of the Structure and Bonding in the Cage Systems S4N4 and S4N4X (X = N+, N−, S, N2S, P+, C, Si, B− and Al−)". Polyhedron 9 (1): 107–111. doi:10.1016/S0277-5387(00)84253-9.
- ^ Jolly, W. L.; Lipp, S. A. (1971). "Reaction of Tetrasulfur Tetranitride with Sulfuric Acid". Inorganic Chemistry 10 (1): 33–38. doi:10.1021/ic50095a008.
- ^ Villena-Blanco, M.; Jolly, W. L.; Egan, B. Z.; Zingaro, R. A. (1967). "Tetrasulfur Tetranitride, S4N4". Inorganic Syntheses 9: 98–102. doi:10.1002/9780470132401.ch26.
- ^ Maaninen, A.; Shvari, J.; Laitinen, R. S.; Chivers, T; (2002). Inorganic Syntheses 33: 196–199. doi:10.1002/0471224502.ch4.
- ^ Kelly, P. F.; Slawin, A. M. Z.; Williams, D. J.; Woollins, J. D. (1992). "Caged explosives: Metal-Stabilized Chalcogen Nitrides". Chemical Society Reviews 21 (4): 245–252. doi:10.1039/CS9922100245.
- ^ Bojes, J.; Chivers, T; Oakley, R. D.; Womershäuser, G.; Schnauber, M. (1989). "Binary Cyclic Nitrogen-Sulfur Anions". Inorganic Syntheses 25: 30–35. doi:10.1002/9780470132562.ch7.
- ^ Bojes, J.; Chivers, T; Oakley, R. D.; Rauchfuss, T. B.; Gammon, S. (1989). "Binary Catena-Nitrogen-Sulfur Anions". Inorganic Syntheses 25: 35–38. doi:10.1002/9780470132562.ch8.
- ^ Dunn, P. J.; Rzepa, H. S. (1987). "The Reaction between Tetrasulphur Tetranitride (S4N4) and Electron-deficient Alkynes. A Molecular Orbital Study". Journal of the Chemical Society, Perkin Transactions 2 1987 (11): 1669–1670. doi:10.1039/p29870001669.
- ^ Greene, R. L.; Street, G. B.; Suter, L. J. (1975). "Superconductivity in Polysulfur Nitride (SN)x". Physical Review Letters 34 (10): 577–579. doi:10.1103/PhysRevLett.34.577.
- ^ Konarev, D. V.; Lyubovskaya, R. N.; Drichko, N. V.; Yudanova, E. I.; Shulga, Yu. M.; Litvinov, A. L.; Semkin V. N.; Tarasov, B. P. (2000). "Donor-Acceptor Complexes of Fullerene C60 with Organic and Organometallic Donors". Journal of Materials Chemistry 10 (4): 803–818. doi:10.1039/a907106g.
- ^ Kelly, P. F.; Woollins, J. D. (1993). "The Reactivity of Se4N4 in Liquid Ammonia". Polyhedron 12 (10): 1129–1133. doi:10.1016/S0277-5387(00)88201-7.
- ^ Kelly, P. F.; Slawin, A. M. Z.; Soriano-Rama, A. (1997). "Use of Se4N4 and Se(NSO)2 in the Preparation of Palladium Adducts of Diselenium Dinitride, Se2N2; Crystal Structure of [PPh4]2[Pd2Br6(Se2N2)]". Dalton Transactions 1997 (4): 559–562. doi:10.1039/a606311j.
- ^ Kelly, P. F.; Slawin, A. M. Z. (1996). "Preparation and Crystal Structure of [(AlBr3)2(Se2N2)], the First Example of a Main-Group Element Adduct of Diselenium Dinitride". Dalton Transactions 1996 (21): 4029–4030. doi:10.1039/DT9960004029.
