Chemistry:Tetrasulfur tetranitride

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Tetrasulfur tetranitride
Stereo, skeletal formula of tetrasulfur tetranitride with some measurements
Ball and stick model of tetrasulfur tetranitride
Space-filling model of tetrasulfur tetranitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| IUPACName = Tetrasulfur tetranitride | SystematicName = 1,3,5,7-tetrathia-2,4,6,8-tetraazacyclooctan-2,4,6,8-tetrayl | Section1 = ! colspan=2 style="background: #f8eaba; text-align: center;" |Identifiers

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3D model (JSmol)

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|- | Section2 = ! colspan=2 style="background: #f8eaba; text-align: center;" |Properties

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| S
4
N
4

|- | Molar mass

| 184.287 g/mol

|- | Appearance | Vivid orange, opaque crystals |-


| Melting point | 187 °C (369 °F; 460 K)

|- | Section3 = | Section4 = | Section5 = | Section6 = }} Tetrasulfur tetranitride is an inorganic compound with the formula S
4
N
4
. 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 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 S
4
N
4
as their parent.

Structure

S
4
N
4
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.[1] One pair of the transannular S atoms have valence 4, and the other pair of the transannular S atoms have valence 2.[citation needed] The bonding in S
4
N
4
is considered to be delocalized, which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are nearly identical. S
4
N
4
has been shown to co-crystallize with benzene and the C
60
molecule.[5]

Properties

S
4
N
4
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 S
4
N
4
compared to its highly stable decomposition products:

2 S
4
N
4
→ 4 N
2
+ S
8

Because one of its decomposition products is a gas, S
4
N
4
can be used as an explosive.[1] Purer samples tend to be more explosive. Small samples can be detonated by striking with a hammer. S
4
N
4
is thermochromic, changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C.[1]

Synthesis

S
4
N
4
was first prepared in 1835 by M. Gregory by the reaction of disulfur dichloride with ammonia,[6] a process that has been optimized:[7]

6 S
2
Cl
2
+ 16 NH
3
→ S
4
N
4
+ S
8
+ 12 [NH
4
]Cl

Coproducts of this reaction include heptasulfur imide (S
7
NH
) and elemental sulfur. A related synthesis employs [NH
4
]Cl
instead:[1]

4 [NH
4
]Cl + 6 S
2
Cl
2
→ S
4
N
4
+ 16 HCl + S
8

An alternative synthesis entails the use of (((CH
3
)
3
Si)
2
N)
2
S
as a precursor with pre-formed S–N bonds. (((CH
3
)
3
Si)
2
N)
2
S
is prepared by the reaction of lithium bis(trimethylsilyl)amide and SCl
2
.

2 ((CH
3
)
3
Si)
2
NLi + SCl
2
→ (((CH
3
)
3
Si)
2
N)
2
S + 2 LiCl

The (((CH
3
)
3
Si)
2
N)
2
S
reacts with the combination of SCl
2
and SO
2
Cl
2
to form S
4
N
4
, trimethylsilyl chloride, and sulfur dioxide:[8]

2 (((CH
3
)
3
Si)
2
N)
2
S + 2 SCl
2
+ 2 SO
2
Cl
2
→ S
4
N
4
+ 8 (CH
3
)
3
SiCl + 2 SO
2

Acid-base reactions

S
4
N
4
 · BF
3

S
4
N
4
serves as a Lewis base by binding through nitrogen to strongly Lewis acidic compounds such as SbCl
5
and SO
3
. The cage is distorted in these adducts.[1]

S
4
N
4
+ SbCl
5
→ S
4
N
4
 · SbCl
5
S
4
N
4
+ SO
3
→ S
4
N
4
 · SO
3

The reaction of [Pt
2
Cl
4
(P(CH
3
)
2
Ph)
2
]
with S
4
N
4
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 H[BF
4
]
to form a tetrafluoroborate salt:

S
4
N
4
+ H[BF
4
] → [S
4
N
4
H]+
[BF
4
]

The soft Lewis acid CuCl forms a coordination polymer:[1]

n S
4
N
4
+ n CuCl → (S
4
N
4
)
n
-μ-(–Cu–Cl–)
n

Dilute NaOH hydrolyzes S
4
N
4
as follows, yielding thiosulfate and trithionate:[1]

2 S
4
N
4
+ 6 OH
+ 9 H
2
O → S
2
O2−
3
+ 2 S
3
O2−
6
+ 8 NH
3

More concentrated base yields sulfite:

S
4
N
4
+ 6 OH
+ 3 H
2
O → S
2
O2−
3
+ 2 SO2−
3
+ 4 NH
3

Metal complexes

S
4
N
4
reacts with metal complexes. The cage remains intact in some cases but in other cases, it is degraded.[2][9] S
4
N
4
reacts with Vaska's complex ([Ir(Cl)(CO)(PPh
3
)
2
]
in an oxidative addition reaction to form a six coordinate iridium complex where the S
4
N
4
binds through two sulfur atoms and one nitrogen atom.

S
4
N
4
as a precursor to other S-N compounds

Many S-N compounds are prepared from S
4
N
4
.[10] Reaction with piperidine generates [S
4
N
5
]
:

24 S
4
N
4
+ 32 C
5
H
10
NH → 8 [C
5
H
10
NH
2
]+
[S
4
N
5
]
+ 8 (C
5
H
10
N)
2
S + 3 S
8
+ 8 N
2

A related cation is also known, i.e. [S
4
N
5
]+
.

Treatment with tetramethylammonium azide produces the heterocycle [S
3
N
3
]
:

8 S
4
N
4
+ 8 [(CH
3
)
4
N]+
[N
3
]
→ 8 [(CH
3
)
4
N]+
[S
3
N
3
]
+ S
8
+ 16 N
2

Cyclo-[S
3
N
3
]
has 10 pi-electrons.

In a related reaction, the use of the bis(triphenylphosphine)iminium azide gives a salt containing the blue [NS
4
]
anion:[10]

4 S
4
N
4
+ 2 [PPN]+
[N
3
]
→ 2 [PPN]+
[NS
4
]
+ S
8
+ 10 N
2

The anion [NS
4
]
has a chain structure described using the resonance [S=S=N–S–S
] ↔ [
S–S–N=S=S]
.

S
4
N
4
reacts with electron-poor alkynes.[11]

Chlorination of S
4
N
4
gives thiazyl chloride.

Passing gaseous S
4
N
4
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 Ag
2
S
catalyzes the conversion of the S
4
N
4
into the four-membered ring S
2
N
2
, which readily polymerizes.[1]

S
4
N
4
+ 8 Ag → 4 Ag
2
S + 2 N
2
x S
4
N
4
→ (SN)
4x

Related compounds

Safety

S
4
N
4
is shock-sensitive. Purer samples are more shock-sensitive than those contaminated with elemental sulfur.[7]

References

  1. Jump up to: 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Greenwood, N. N.; Earnshaw, A. (1997). Chemical Elements (2nd ed.). Boston, MA: Butterworth-Heinemann. pp. 721–725. 
  2. Jump up to: 2.0 2.1 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. Konarev, D. V.; Lyubovskaya, R. N.; Drichko, N. V. et al. (2000). "Donor-Acceptor Complexes of Fullerene C60 with Organic and Organometallic Donors". Journal of Materials Chemistry 10 (4): 803–818. doi:10.1039/a907106g. 
  6. Jolly, W. L.; Lipp, S. A. (1971). "Reaction of Tetrasulfur Tetranitride with Sulfuric Acid". Inorganic Chemistry 10 (1): 33–38. doi:10.1021/ic50095a008. https://escholarship.org/uc/item/7xj1q0zf. 
  7. Jump up to: 7.0 7.1 Villena-Blanco, M. et al. (1967). S. Y. Tyree Jr. ed. "Tetrasulfur Tetranitride, S4N4". Inorganic Syntheses 9: 98–102. doi:10.1002/9780470132401.ch26. 
  8. Maaninen, A.; Shvari, J.; Laitinen, R. S.; Chivers, T (2002). Coucouvanis, Dimitri. ed. "Compounds of General Interest". Inorganic Syntheses 33: 196–199. doi:10.1002/0471224502.ch4. ISBN 9780471208259. 
  9. 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. 
  10. Jump up to: 10.0 10.1 Bojes, J. et al. (1989). Allcock, H. R.. ed. "Binary Cyclic Nitrogen-Sulfur Anions". Inorganic Syntheses 25: 30–35. doi:10.1002/9780470132562.ch7. ISBN 9780470132562. 
  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. Bibcode1975PhRvL..34..577G. 
Salts and covalent derivatives of the nitride ion