Complexation between Cd(SbF6)2 and the ligands Ph3PE (E = S or Se), Ph2P(E)(CH2)nP(E)Ph2 (n = 1 or 2, E = O, S or Se; n = 3, E = Se), [Ph2P(E)CH2]3CMe (E = S or Se) and Ph2P(E)(CH2)2PPh(E)(CH2)2P(E)Ph2 (E = O, S, or Se) in liquid SO2 has been studied, mainly by low-temperature 31P nmr spectroscopy. With the sulfides and selenides the maximum donor atom/Cd ratio observed is four, as shown by the limiting low temperature spectra of (Ph3PE)4Cd2+ (E = S or Se), [CH2(PPh2(Se))2]2Cd2+, and [Ph2P(E)CH2CMe(CH2PPh2(E))2]2Cd2+ (E = S or Se). The last two complexes both contain a potentially tridentate ligand behaving in a bidentate manner and their spectra are unexpectedly complicated due, perhaps, to conformational effects. Slow exchange spectra of [Ph2P(E)(CH2)2PPh(E)(CH2)2PPh2(E)]Cd2+ (E = S or Se) show that in each complex the ligand behaves in a tridentate manner. For the preceding complexes, two-bond 111/113Cd–31P coupling is observed at the donor sites, and for the selenides a reduction in |1J(31P—77Se)| on complexation further identifies the bound —PSe groups.The maximum coordination number appears to be six in the complexes of the phosphine oxides. Both 2:1 and 3:1 L:Cd complexes exist for both of the bidentate ligands Ph2P(O)(CH2)nP(O)Ph2 (n = 1 or 2) whereas in the system Ph2P(O) (CH2)2P(O)Ph(CH2)2P(O)Ph2–Cd2+ the species identified is the presumably six-coordinate 2:1 complex. For comparison, the six-coordinate complex [{CH2(PPh2(O))2}3Hg]2+ has been identified in solution also.Competition studies between the dioxides, disulfides, and diselenides of the diphosphines show that the disulfides and diselenides cannot compete with the dioxides for cadmium, but that the diselenides can compete with the disulfides to a limited extent.

Dean, P. A. W., & Hughes, M. K. (1980). A 31P nuclear magnetic resonance spectroscopic study of complexes of cadmium(II) with some phosphine oxides, sulfides, and selenides. Canadian Journal of Chemistry, 58(2), 180–190.