Hexasulphur tetranitrogen dichloride, S6N4Cl2: crystal growth and crystal structure

Abstract

Crystals of the title compound (commonly called thiodithiazyl chloride) are orthorhombic, space group Pbca, with a= 7.88(1), b= 14.46(1), c= 8.19(1)Å, and Z= 4. The structure was refined to R= 0.031 using 563 (of the 792 unique) measured intensities for which l > 3σ(l). The dimeric cation contains two centrosymmetric planar S₃N₂ rings in a chair (trans) conformation. Distances are S(1)–N(1) 1.563(5), N(1)–S(3) 1.618(4), S(2)–S(3) 2.131(2), S(2)–S(3^I) 2.916(2), and Cl–S(2,3) 2.842(2), 2.858(2)Å. The dihedral angle between the S₃N₂ ring plane and the central S₄ ring is 110.4(3)°. Crystals of S₆N₄Cl₂ were grown by three different methods based on (i) a reversible temperature-dependent ring expansion–contraction (S₆N₄Cl₂↔ S₄N₃Cl) equilibrium in SO₂–SOCl₂ mixtures, (ii) a complex chemical transport (vapour–liquid–solid) in a sealed tube containing (initially) S₃N₂Cl₂ and liquid SO₂, and (iii) a controlled slow reaction of S₃N₂Cl₂ with liquid SO₂. The last method is a particularly convenient laboratory synthesis of pure S₆N₄Cl₂. Solid S₆N₄Cl₂ shows a strong e.s.r. signal which is independent of temperature (in the range –139 to +22 °C), indicating the presence of a little monomer.