Tetrasulfur tetranitride explained

Tetrasulfur tetranitride is an inorganic compound with the formula . This vivid orange, opaque, crystalline explosive 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 the properties of atoms are so highly similar, they often form extensive families of covalently bonded structures and compounds. Indeed, a large number of S-N and S-NH compounds are known with as their parent.

Structure

adopts an unusual “extreme cradle” structure, with D2d point group symmetry. It can be viewed as a derivative of a (hypothetical) eight-membered ring (or more simply a 'deformed' 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. One pair of the transannular S atoms have valence 4, and the other pair of the transannular S atoms have valence 2. The bonding in is considered to be delocalized, which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are nearly identical. has been shown to co-crystallize with benzene and the molecule.[5]

Properties

is stable to air. It is, however, unstable in the thermodynamic sense with a positive enthalpy of formation of +460 kJ/mol. This endothermic enthalpy of formation originates in the difference in energy of compared to its highly stable decomposition products:

S4N4 is shock and friction sensitive and because one of its decomposition products is a gas, is considered a primary explosive.[6] Purer samples tend to be more sensitive. Small samples can be detonated by striking with a hammer. is thermochromic, changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C.

Synthesis

was first prepared in 1835 by M. Gregory by the reaction of disulfur dichloride with ammonia,[7] a process that has been optimized:[8]

Coproducts of this reaction include heptasulfur imide and elemental sulfur, and the latter equilibrates with more and ammonium sulfide:[9]

A related synthesis employs instead:

An alternative synthesis entails the use of as a precursor with pre-formed S–N bonds. is prepared by the reaction of lithium bis(trimethylsilyl)amide and .

The reacts with the combination of and to form, trimethylsilyl chloride, and sulfur dioxide:[10]

Acid-base reactions

serves as a Lewis base by binding through nitrogen to strongly Lewis acidic compounds such as and . The cage is distorted in these adducts.

The reaction of with 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 to form a tetrafluoroborate salt:

The soft Lewis acid CuCl forms a coordination polymer:

Dilute NaOH hydrolyzes as follows, yielding thiosulfate and trithionate:

More concentrated base yields sulfite:

Metal complexes

reacts with metal complexes. The cage remains intact in some cases but in other cases, it is degraded.[2] [11] reacts with Vaska's complex (in an oxidative addition reaction to form a six coordinate iridium complex where the binds through two sulfur atoms and one nitrogen atom.

as a precursor to other S-N compounds

Many S-N compounds are prepared from .[12] Reaction with piperidine generates :

A related cation is also known, i.e. .

Treatment with tetramethylammonium azide produces the heterocycle :

Cyclo- has 10 pi-electrons.

In a related reaction, the use of the bis(triphenylphosphine)iminium azide gives a salt containing the blue anion:

The anion has a chain structure described using the resonance .

reacts with electron-poor alkynes.[13]

Chlorination of gives thiazyl chloride.

Passing gaseous over silver metal yields the low temperature superconductor polythiazyl or polysulfurnitride (transition temperature (0.26±0.03) K[14]), often simply called "(SN)x". In the conversion, the silver first becomes sulfided, and the resulting catalyzes the conversion of the into the four-membered ring, which readily polymerizes.

Related compounds

Safety

is a categorized as a primary explosive that is shock and friction sensitive. While comparable to pentaerythritol tetranitrate (PETN) in terms of impact sensitivity, its friction sensitivity is equal to or even lower than lead azide.[15] Purer samples are more shock-sensitive than those contaminated with elemental sulfur.[8]

Notes and References

  1. Book: Greenwood . N. N. . Earnshaw . A. . Chemical Elements . 2nd . Butterworth-Heinemann . Boston, MA . 1997 . 721–725 .
  2. Book: Chivers, T. . A Guide To Chalcogen-Nitrogen Chemistry . World Scientific Publishing . Singapore . 2004 . 981-256-095-5 .
  3. Sharma . B. D. . Donohue . J. . The Crystal and Molecular Structure of Sulfur Nitride, S4N4 . . 1963 . 16 . 9 . 891–897 . 10.1107/S0365110X63002401 . 1963AcCry..16..891S .
  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) . Henry Rzepa . Rzepa . H. S. . Woollins . J. D. . . 1990 . 9 . 1 . 107–111 . 10.1016/S0277-5387(00)84253-9 .
  5. Konarev . D. V. . Lyubovskaya . R. N. . Drichko . N. V. . Yudanova . E. I. . Shulga . Yu. M. . Litvinov . A. L. . Semkin . V. N. . Tarasov . B. P. . 3 . Donor-Acceptor Complexes of Fullerene C60 with Organic and Organometallic Donors . . 2000 . 10 . 4 . 803–818 . 10.1039/a907106g .
  6. Web site: Assessment . US EPA National Center for Environmental . 2009-03-15 . Analysis of the Explosive Properties of Tetrasulfur Tetranitride, S4N4 . 2024-05-24 . hero.epa.gov . en.
  7. Jolly . W. L.. Lipp . S. A.. Reaction of Tetrasulfur Tetranitride with Sulfuric Acid. Inorganic Chemistry . 10 . 1. 33–38 . 1971. 10.1021/ic50095a008.
  8. Book: Villena-Blanco . M. . Jolly . W. L. . Tetrasulfur Tetranitride, S4N4 . etal . . 1967 . 9 . 98–102 . 10.1002/9780470132401.ch26 . 978-0-470-13168-8 . Inorganic Syntheses . S. Y. Tyree Jr.
  9. Book: Non-aqueous solvents. 44. Ludwig F.. Audrieth. Jacob. Kleinberg. John Wiley & Sons. New York. 1953. 52-12057.
  10. Book: Maaninen . A. . Shvari . J. . Laitinen . R. S. . Chivers . T . Compounds of General Interest . . 2002 . 33 . 196–199 . 10.1002/0471224502.ch4 . Coucouvanis . Dimitri . Inorganic Syntheses. 9780471208259 .
  11. Kelly . P. F. . Slawin . A. M. Z. . Williams . D. J. . Woollins . J. D. . Caged explosives: Metal-Stabilized Chalcogen Nitrides . . 1992 . 21 . 4 . 245–252 . 10.1039/CS9922100245 .
  12. Book: Bojes . J. . Chivers . T. . Oakley . R. D. . Binary Cyclic Nitrogen-Sulfur Anions . etal . Inorganic Syntheses . . 1989 . 25 . 30–35 . 10.1002/9780470132562.ch7 . Allcock . H. R. . 9780470132562 .
  13. The Reaction Between Tetrasulphur Tetranitride (S4N4) and Electron-deficient Alkynes. A Molecular Orbital Study . Dunn . P. J. . Henry Rzepa . Rzepa . H. S. . . 1987 . 1987 . 11 . 1669–1670 . 10.1039/p29870001669 .
  14. Greene . R. L. . Street . G. B. . Suter . L. J. . Superconductivity in Polysulfur Nitride (SN)x . . 1975 . 34 . 10 . 577–579 . 10.1103/PhysRevLett.34.577 . 1975PhRvL..34..577G.
  15. Web site: Assessment . US EPA National Center for Environmental . 2009-03-15 . Analysis of the Explosive Properties of Tetrasulfur Tetranitride, S4N4 . 2024-05-24 . hero.epa.gov . en.