Tetrasulfur tetranitride

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Tetrasulfur tetranitride
The structure of tetrasulfur tetranitrideThe structure of tetrasulfur tetranitride
General
Systematic name Tetranitrogen tetrasulfide
tetrasulfur nitride
Molecular formula S4N4
Molar mass 184.29 g/mol
Appearance Orange solid
CAS number [28950-34-7]
Properties
Solubility in water Insoluble
Solubility in other solvents CS2, benzene
Melting point 187 °C (460 K)
IR 928 768 727 700
630 553 548 and 529 cm-1
NMR 15N NMR: δ -246
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Tetrasulfur tetranitride is an inorganic compound with the formula S4N4. This gold-poppy coloured solid is one of the most important sulfur nitride, i.e. compounds that contain primarily the elements sulfur and nitrogen. It is a precursor to many S-N compounds and has attracted much interest for its unusual structure and bonding.[1]

Nitrogen and sulfur have similar ability to attract electrons, a property known as electronegativity. 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. In addition a selenium version (Se4N4 is known and has been the subject of some research, for example see[2][3])

Contents

[edit] Structure of S4N4

S4N4 adopts an unusual “extreme cradle” structure, which was determined in 1944. The structure of S4N4 can be viewed as an eight membered ring of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are further bonded, resulting in a cage-like structure consisting of interlocking five-membered S3N2 rings. The nature of the "transannular" S-S interactions is a matter of debate (and computational investigation[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.

[edit] Properties

S4N4 is stable to air. It is, however, unstable in the thermodynamic sense with a positive heat of formation of 460 kJ/mole). This endothermic heat of formation anticipates its inherent instability, and originates in the difference in energy of S4N4 compared to its highly stable decomposition products:

S4N4 → 2 N2 + 0.5S8

It is not really very unusual for complex molecules to be unstable in a thermodynamic sense yet stable kinetically; this situation describes the great majority of organic compounds. This combination of kinetic stability and thermodynamic instability is, however, 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]

[edit] Synthesis

Until recently, S4N4 was prepared by the reaction of ammonia with SCl2 in carbon tetrachloride followed by extraction into dioxane.[5]

6 SCl2 + 16 NH3 → S4N4 + S8 + 12 NH4Cl

A related synthesis employs NH4Cl in place of ammonia:[1]

4 NH4Cl + 6 S2Cl2 → S4N4 + 16 HCl + S8


A newer 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.[6]

[(CH3)3Si)2N]2S + SCl2 + SO2Cl2 → S4N4 + 4 (CH3)3SiCl + SO2

[edit] Acid-base reactions

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 delocolization of electrons may be disrupted.[1] In addition adducts of aluminium chloride with Se2N2 have been isolated, this is formed from Se4N4.[7]

S4N4 + SbCl5 → S4N4.SbCl5
S4N4 + SO3 → S4N4.SO3

It is protonated by HBF4:

S4N4 + HBF4 → S4N4H+BF4

The soft Lewis acid CuCl forms a polymer with intact S4N4 rings as the bridging ligands:[1]

nS4N4 + nCuCl → (S4N4)n-μ-(-Cu-Cl-)n

S4N4 is sensitive to hydrolysis in the presence of base. Dilute NaOH hydrolyzes S4N4 as follows:[1]

2S4N4 + 6 OH- + 9 H2O → S2O32- + 2 S3O62- + 8 NH3

Whereas more concentrated base yields sulfite:

S4N4 + 6 OH- + 3 H2O → S2O32- + 2 SO32- + 4 NH3

[edit] Reactions with metal complexes

For an overview of this topic a 1992 review can read.[8]

[edit] Reactions of S4N4 where the S4N4 remains intact

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 can be though of as forming by the breaking of one S-N bond (in the oxidative addition) followed by the coordination of the lone pair on another sulfur to form a dative bond. This chemistry could be repeated with Zeises' salt to form a platinium version of the iridium compound.

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.

[edit] Reactions of S4N4 where the S4N4 does not remain intact

The reaction of S4N4 with the [Pd2Cl6]2- anion forms a series of three different palladium complexes in which the S4N4 ring has been fragmented.

[edit] S4N4 as a precursor to other S-N compounds

Many important S-N compounds are prepared from S4N4.[9] Reaction with piperidine generates [S4N5]−:

3 S4N4 + 4 C5H10NH → (C5H10NH2)+[S4N5]- + (C5H10N)2S + 3/8 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 + 4 NMe4N3 → NMe4[S3N3] + 1/8 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 the blue perthionitrite salt:

2 S4N4 + PPN(N3) → PPN[NS3] + 1/2 S8 + 5 N2

The anion NS3- is a chain described often as S=N-S-S-.

[edit] Reaction with acetylenes

S4N4 reacts with electron poor acetylenes.[10]

[edit] "SNx"

Passing gaseous S4N4 over silver metal yields the low temperature superconductor polysulfurnitride (transition temperature (0.26±0.03) K[11]), known as "(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

[edit] Miscellaneous facts

S4N4 has been shown to co-crystallize with benzene and the C60.[12]

[edit] Safety

S4N4 is shock-sensitive, thus grinding solid samples should be avoided. Purer samples are reportedly more sensitive than those contaminated with elemental sulfur.

[edit] External links

[edit] References

  1. ^ a b c d e f g h i Greenwood, N. N.; Earnshaw, A. Chemical Elements; 2nd edition; Butterworth-Heinemann: Boston, MA, 1997, pp 721-725.
  2. ^ Kelly, P.F. and Woollins, J.D., The Reactivity of Se4N4 in Liquid Ammonia, Polyhedron, 12, 1993, pp 1129-1133.
  3. ^ Kelly, P.F., Slawin, A.M.Z. and Soriano-Rama, A., Use of Se4N4 and Se(NSO)2 in the preparation of palladium adducts of diselenium dinitride, Se2N2; crystal structure of [PPh4]2[Pd2Br6(Se2N2), Journal of the Chemical Society, Dalton Transactions, 1997, pp 559-562
  4. ^ 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[-]). H. S. Rzepa and J. D.Woollins, Polyhedron , 1990, 9 , 107.
  5. ^ Villena-Blanco, M.; Jolly, W.L.; Tyree, S.Y. Ed.: Inorganic synthesis; Wiley: New York, NY, 1967; Vol. 9, pp. 98-102
  6. ^ Maaninen, A.; Shvari, J.; Laitinen, R.S.; Chivers, T; Inorganic Synthesis; (2002) Vol. 33, pp. 196-199
  7. ^ Kelly, P.F. and Slawin, A.M.Z., Preparation and crystal structure of [(AlBr3)2(Se2N2)], the first example of a main-group element adduct of diselenium dinitride, Journal of the Chemical Society, Dalton Transactions, 1996, pp 4029-4030
  8. ^ Paul. F. Kelly, Alexandra. M.Z. Slawin, David J. Williams and J. Derek Woollins, Chemical Society Reviews, 1992, 245
  9. ^ Bojes, J.; Chivers, T; Oakley, R. D. Inorganic Synthesis (1989) Vol 25, pp. 30-40.
  10. ^ The Reaction between Tetrasulphur Tetranitride (S4N4) and Electron-deficient Alkynes. A Molecular Orbital Study. P. J. Dunn and H. S. Rzepa, J. Chem. Soc., Perkin Trans. 2 , 1987, 1669-1670
  11. ^ R. L. Greene, G. B. Street and L. J. Suter, Superconductivity in Polysulfur Nitride (SN)x, Phys. Rev. Lett. 34, 577–579 (1975) DOI:10.1103/PhysRevLett.34.577
  12. ^ Konarev, D.V. et al. "Donor-acceptor Complexes of Fullerene C60 with Organic and Organometallic Donors" Journal of Materials Chemistry (2000) Volume 10, pages 803-818.

[edit] Further reading

  • Chivers, T. “A Guide To Chalcogen-Nitrogen Chemistry” World Scientific Publishing Company: Singapore; 2004. ISBN 981-256-095-5
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