A new assembly of diiodine molecules at the triphenylphosphine sulfide template†

Abstract

The new I₂ adduct TPPS·3I₂ (TPPS = triphenylphosphine sulfide) has been synthesized and characterised by X-ray diffraction on a single crystal. It consists of a TPPS·I₂ 1∶1 molecular adduct interacting with two further diiodine molecules in a “head to tail” sequence to give an overall TPPS·I₂· · ·I₂· · ·I₂ arrangement in the asymmetric unit. Considering the I· · ·I interactions below 3.6 Å, five of the six iodine atoms of the asymmetric unit are arranged in infinite polycyclic ribbons. The iodine atoms, to which the TPPS molecules are connected, are almost perpendicular appendages on opposite sides of each ribbon. Weaker interactions between the ribbons give rise to unprecedented continuous stepped layers of diiodine molecules anchored to TPPS donor units. The structural features of TPPS·3I₂ are discussed in comparison with those of the previously reported 2TPPS·3I₂, TPPS·I₂, TPPS·IBr and TPPS·ICl, and its FT-Raman spectrum compared with those of 2TPPS·3I₂ and TPPS·I₂. A re-examination of the equilibrium reaction between TPPS and I₂ by ³¹P NMR confirms the formation of the 1∶1 adduct in CH₂Cl₂ solution and gives a formation constant value of 137 ± 11 dm³ mol^–1.