Abstract Tetraallyldiphosphine disulphide P 2(C 3H 5) 4S 2 has a centrosymmetric trans structure in the crystal. This structure is retained in solution, with no evidence of isomerism resulting from restricted rotations of the allyl side-chains about the PC bonds. It is not possible to determine the internal allyl-group conformation ( cis or gauche) unambiguously from the spectrosopic data. The molecule forms relatively few stable complexes; those which are obtained contain the ligand in a chelate (possibly cis) conformation. The PP stretching frequency rises from 466 to 490 cm −1 on complex formation and skeletal frequencies in the coordinated ligand are generally similar to those in the corresponding tetraethyl, tetrapropyl and tetrabutyl compounds.