Q5(d). S₄N₄ from S₂Cl₂ and NH₃; S₂N₂ and (SN)ₓ

1. A: in CCl₄, S₂Cl₂ and ammonia give tetrasulfur tetranitride; the mole ratio 16:6=2.67 fixes the equation: 2pt] 6S₂Cl₂ + 16NH₃ → S₄N₄ + S₈ + 12NH₄Cl
2. Structure of A: S₄N₄ is an eight-membered S–N ring folded into a cage (D_(2d)): the four N atoms form a square plane and the four S atoms a flattened tetrahedron, with two transannular S…S interactions across the cage. All S–N bonds are equal (delocalised). Orange solid, explosive on shock or heating.
3. B: hot silver wool removes sulfur as Ag₂S and cracks the cage into the four-membered ring: S₄N₄ + 4Ag → S₂N₂ + 2Ag₂S + N₂ S₂N₂ is a square planar ring of alternating S and N; colourless, more sensitive than S₄N₄, exploding above room temperature.
4. C: on hot quartz wool (no silver to take up sulfur) the S₄N₄ vapour simply cracks, S₄N₄ → 2 S₂N₂; the S₂N₂ condenses and polymerises (slowly at 0°C, in the solid) to polythiazyl (SN)ₓ, a zig-zag chain of alternating S and N. It is golden (bronze) with a metallic lustre, conducts like a metal along the chain and becomes superconducting below 0.3 K: the first superconductor without a metal.
5. Both B and C keep the S: N ratio 1: 1 of A; only the size of the ring or chain changes.

Application. (SN)ₓ is studied as a one-dimensional conductor; partial bromination gives (SNBr_(0.4))ₓ, a better conductor, the model for conducting polymers.