Disulfur dinitride

Disulfur dinitride is the chemical compound with the formula S₂N₂.

Disulfur dinitride

Space-filling model of disulfur dinitride
Names
Preferred IUPAC name Disulfur dinitride
Systematic IUPAC name 1λ4,3,2,4-Dithiadiazete
Other names Cyclic sulfur(II,IV) nitride 1,3-dithia-2,4-diazacyclobutan-2,4-diyl
Identifiers
CAS Number	25474-92-4
3D model (JSmol)	Interactive image
ChEBI	CHEBI:37756
ChemSpider	124561
PubChem CID	141213
CompTox Dashboard (EPA)	DTXSID401027576
InChI InChI=1S/N2S2/c1-3-2-4-1 Key: HGFWWXXKPBDJAH-UHFFFAOYSA-N
SMILES S1N=S=N1
Properties
Chemical formula	S2N2
Molar mass	92.1444 g/mol
Appearance	colourless crystals
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation and reactions

Passing gaseous S₄N₄ over silver metal wool at 250–300 °C at low pressure (1 mmHg) yields cyclic S₂N₂. The silver reacts with the sulfur produced by the thermal decomposition of the S₄N₄ to form Ag₂S, and the resulting Ag₂S catalyzes the conversion of the remaining S₄N₄ into the four-membered ring S₂N₂,^[1]

S₄N₄ + 8 Ag → 4 Ag₂S + 2 N₂

S₄N₄ → 2 S₂N₂

An alternative uses the less explosive S₄N₃Cl.^{[2][clarification needed]}

S₂N₂ decomposes explosively above 30°C, and is shock sensitive.^[1] It readily sublimes, and is soluble in diethyl ether. Traces of water cause it to polymerize into S₄N₄.^[2] In the solid state it spontaneously polymerizes forming (SN)_n.^[1] It forms adducts with Lewis acids via a nitrogen atom, e.g. S₂N₂·BCl₃, S₂N₂·2AlCl₃, S₂N₂·SbCl₅, S₂N₂·2SbCl₅.^[2][3]

Structure and bonding

The S₂N₂ molecule is a four-membered ring, with alternating S and N atoms. The S₂N₂ molecule is a resonance hybrid of many contributing structures. In one of those structures, one S atom has valence 4 and the other S atom has valence 2, and both N atoms has valence 3. In the other structure both S atoms have valence 2 and both N atoms has valence 3, and one of the S atoms has a charge of +1, and one of the N atoms has a charge of −1. The molecule is almost square and planar. The S–N bond lengths are 165.1 pm and 165.7 pm and the bond angles are very close to 90°.^[1] The S₂N₂ molecule is isoelectronic with the cyclic S2+4 dication and has 6π electrons.^[2] The bonding has been investigated using a spin-coupled valence bond method ^[4] and is described as having four framework sigma bonds, with the N atoms bearing a high negative charge and the S atoms a corresponding positive charge. Two π electrons from the sulfur atoms are coupled across the ring making the molecule overall a singlet diradical.

See also

• Sulfur nitride
• Tetrasulfur tetranitride
• Polythiazyl
• Square planar molecular geometry