Crystal structure of triphenylphosphine sulfide diiodine; the first crystallographically characterised 1∶1 molecular charge-transfer complex of a tertiary phosphine sulfide with diiodine

Abstract

In CH₂Cl₂ solution, Ph₃PS and diiodine react to form a molecular 1∶1 charge-transfer complex. The complex has been studied in solution using ³¹P-{H} NMR and UV/VIS spectroscopy. Single-crystal X-ray diffraction and solid-state ³¹P-{H} NMR studies of Ph₃PS·I₂ show that the molecular structure is maintained in the solid phase. The structure of Ph₃PS·I₂ is novel and contradicts previous results which indicated that a 1∶1 (Ph₃PS∶I₂) complex could not be isolated in the solid state. The I–I distance [2.823(1) Å] and the S–I distance [2.753(2) Å] in Ph₃PS·I₂ are comparable with those in charge-transfer complexes of related sulfur donors. However, the I–I distance in Ph₃PS·I₂ is shorter than that in Ph₃PSe·I₂ reflecting the weaker donor power of the Ph₃PS towards diiodine. The NMR spectroscopic results on Ph₃PS·I₂ and the analogous Ph₃PO and Ph₃PSe compounds indicate that the stability of the Ph₃PE·I₂ complexes increases in the order E = Se > S  O.