S4N4

Tetrasulfur tetranitride

Names
Other names Cyclic sulfur(III) nitride tetramer 1λ4,3,5λ4,7,2,4,6,8-Tetrathiatetrazocine 1,3,5,7-tetrathia-2,4,6,8-tetraazacyclooctan-2,4,6,8-tetrayl
Identifiers
CAS Number	28950-34-7 N
3D model (JSmol)	Interactive image Interactive image
ChemSpider	124788 Y
PubChem CID	141455
InChI InChI=1S/N4S4/c1-5-2-7-4-8-3-6-1 Y Key: LTPQFVPQTZSJGS-UHFFFAOYSA-N Y
SMILES n1snsnsns1 N1=[S]N=[S]N=[S]N=[S]1
Properties
Chemical formula	S 4N 4
Molar mass	184.287 g mol−1
Appearance	Vivid orange, opaque crystals
Melting point	187 °C (369 °F; 460 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
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.

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 S₄N₄ as their parent.

S₄N₄ adopts an unusual “extreme cradle” structure, with D_2dpoint 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. 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 but has been explained in the context of molecular orbital theory. 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 nearly identical. S₄N₄ has been shown to co-crystallize with benzene and the C₆₀ molecule.

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 originates in the difference in energy of S₄N₄ compared to its highly stable decomposition products: