Preparation and X-ray crystal structure of (S3N2)2NAsF6, containing the bis(thiodithiazyl)aminylium(1+) cation

Abstract

Crystalline (S₃N₂)₂NAsF₆ was prepared in ca. 60% yield from a 1 : 1 mixture of S₄N₄ and S₂NAsF₆ in liquid SO₂ at 0 °C, and its structure determined by X-ray crystallography. The compound crystallises in the monoclinic space group C2/c with unit-cell dimensions a= 17.343(6), b= 17.103(6), c= 16.737(9)Å, β= 98.29(3)°, and Z= 16. The structure was solved by direct methods and refined by least-squares techniques to a final R of 0.11 for 2 308 observed reflections. (S₃N₂)₂NAsF₆ is essentially ionic with sulphur–fluorine cation–anion contacts. The (S₃N₂)₂N⁺ cation is the first example of a monobridged bicyclic sulphur–nitrogen cation, and consists of two thiodithiazyl (S₃N₂) groups connected together by a bridging nitrogen atom attached to a sulphur atom of each S₃N₂ ring. The S₃N₂ rings are cis with respect to the bridging nitrogen atom, and are essentially eclipsed with respect to the SNS bridge. (S₃N₂)₂NAsF₆ reacts with CsN₃ in liquid SO₂ solution yielding impure poly(sulphur nitride) and CsAsF₆. Solutions of (S₃N₂)₂NAsF₆ in liquid SO₂ slowly disproportionate to S₄N₂AsF₆ and S₄N₄. The i.r. spectrum of (S₃N₂)₂NAsF₆ is also reported.