A crystal structure determination showed that in diphenylbismuth thiocyanate the thiocyanate group bridges between pairs of bismuth atoms to give infinite chains in which alternate bismuth atoms are co-ordinated to either two nitrogen or two sulfur atoms. The conformation of the resulting chain is a 'rectangular spiral', in contrast to the 'triangular spiral' structure of the related diphenylantimony thiocyanate. Unstable diphenylantimony selenocyanate has also been prepared and the complexity in the C-N stretching region of the IR spectrum suggests a structure simitar to that of the thiocyanate analogue. Diphenylarsenic thiocyanate is a liquid at room temperature and a conventional 1'3thiocyanate-bridged structure is suggested from IR data.We have recently shown that two diarylantimony(I1r) thiocyanates exhibit totally different crystal structures. In diphenylantimony thiocyanate, the thiocyanate group bridges between pairs of antimony atoms to generate an infinite chain, while in bis(2,6dimethylphenyl)antimony thiocyanate, steric effects from the two o-methyl substituents are sufficient to prevent thiocyanate bridging and the structure consists of discrete N-bonded monomers. Thiocyanate bridging in the diphenyl compound leads, however, to an unusual and probably unique structure type. The asymmetric unit consists of three molecules in which two of the independent thiocyanate groups can be considered as being primarily N-bonded while the orientation of the third is reversed and is primarily S-bonded. The bridging thiocyanate groups occupy axial positions in a pseudo-trigonal-bipyramidal arrangement about antimony and this in conjunction with angles of ca. 170" at nitrogen and ca. 90" at sulfur forces a 'triangular spiral' structure on the chains of molecules so generated.Phenyl-substituted thiocyanates of two of the elements close to antimony in the Periodic Table , i.e. triphenyltin thiocyanate and triphenyltehrium thiocyanate, have more conventional structures. The former shows regular 1,3-thiocyanate bridging leading to infinite zigzag chains,2 while in the latter, although the structure is basically ionic, there are di-and tetra-meric units in which thiocyanate groups bridge between pairs of tellurium atoms., To examine further the parameters which may have a bearing on the unusual diphenylantimony thiocyanate structure, we have investigated the chemistry of analogues in which: (a) the central atom is either arsenic or bismuth and (b) in which antimony remains the central atom and the pseudo-halide is exchanged for either cyanate or selenocyanate. ExperimentalAll reactions were carried out with dried and redistilled solvents under an atmosphere of nitrogen.

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The thiocyanate group can bond via sulphur or nitrogen or bridge between two centres, but in diphenylantimony thiocyanate, unusual bridging gives antimony atoms coordinated by, respectively, two sulphur atoms, two nitrogen atoms and one atom of each type, allowing development of a curious infinite 'triangular spiral' structure in the solid state.