The crystal structure of the title compound (I) has been solved by Patterson and heavy-atom Fourier methods and refined by full-matrix least-squares methods from single-crystal X-ray diffractometer data to a final R of 3·2%(1552 observed reflections). Crystals are monoclinic, space group P21/a, with a= 14·978(10), b= 13·107(6), c= 11·588(8)A, β= 124·84(3)° with Z= 4. The triphenylphosphine group is bonded through nitrogen to an alternating S3N3 ring, five members of which are planar.