Tetrasulfur tetranitride

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Tetrasulfur tetranitride
Stereo, skeletal formula of tetrasulfur tetranitride with some measurements
Ball and stick model of tetrasulfur tetranitride Space-filling model of tetrasulfur tetranitride
Identifiers
CAS number 28950-34-7 N
PubChem 141455
ChemSpider 124788 YesY
Jmol-3D images Image 1
Image 2
Properties
Molecular formula N
4
S
4
Molar mass 184.287 g mol−1
Appearance Vivid orange, opaque crystals
Melting point 187 °C (369 °F; 460 K)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
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.

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]

S
4
N
4
was first prepared in 1835 by M. 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·BF3

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]

  1. ^ 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. 
  2. ^ a b Chivers, T. (2004). A Guide To Chalcogen-Nitrogen Chemistry. Singapore: World Scientific Publishing. ISBN 981-256-095-5. 
  3. ^ 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. 
  4. ^ 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. 
  5. ^ Jolly, W. L.; Lipp, S. A. (1971). "Reaction of Tetrasulfur Tetranitride with Sulfuric Acid". Inorganic Chemistry 10 (1): 33–38. doi:10.1021/ic50095a008.  edit
  6. ^ Villena-Blanco, M.; Jolly, W. L.; Egan, B. Z.; Zingaro, R. A. (1967). "Tetrasulfur Tetranitride, S
    4
    N
    4
    ". Inorganic Syntheses 9: 98–102. doi:10.1002/9780470132401.ch26.
     
  7. ^ Maaninen, A.; Shvari, J.; Laitinen, R. S.; Chivers, T; (2002). Inorganic Syntheses 33: 196–199. doi:10.1002/0471224502.ch4. 
  8. ^ 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. 
  9. ^ 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. 
  10. ^ 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. 
  11. ^ 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. 
  12. ^ 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. 
  13. ^ 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. 
  14. ^ 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. 
  15. ^ 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. 
  16. ^ 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.