Crystal and molecular structure of bis-tetraphenylarsonium-tris-(cis-1,2-dicyano-1,2-ethylenedithiolato)Fe(IV)

The crystal structure of bis-tetraphenylarsonium-tris-(cis-1,2-dicyano-1,2-ethylenedithiolato)Fe(IV), [(C₆H₅)₃As]₂Fe[S₂C₂(CN)₂]₃, has been determined using 3154 independent, non-zero reflexions collected by counter techniques. The substance crystallizes in the monoclinic system: space groupI2/a,a = 20·153(8),b = 13·411(5),c = 21·497(8) Å and = 95·28(8) °;D_m = 1·41(2),D_c = 1·43 g cm^–3 andZ = 4. The structure consists of Ph₄As⁺ cations in general positions and tris-(cis-1,2-dicyano-1,2-ethylenediothiolato)Fe(IV) anions on two-fold axes. Although the coordination around the arsenic atom is tetrahedral, the overall symmetry of the cation is 1 (C₁), probably because the phenyl rings are rotated to accommodate the requirements of packing. The coordination of the six sulphur atoms about the iron atom is trigonal antiprismatic, approximating closely to an octahedron: for any pair oftrans sulphur atoms, the S-Fe-S angle is about 171 °.