A new assembly of diiodine molecules at the triphenylphosphine sulfide template

The new I-2 adduct TPPS . 3I(2) (TPPS = triphenylphosphine sulfide) has bee n synthesized and characterised by X-ray diffraction on a single crystal. I t consists of a TPPS . I-2 1 : 1 molecular adduct interacting with two furt her diiodine molecules in a "head to tail" sequence to give an overall TPPS . I-2 ... I-2 ... I-2 arrangement in the asymmetric unit. Considering the I ... I interactions below 3.6 Angstrom, five of the six iodine atoms of th e asymmetric unit are arranged in infinite polycyclic ribbons. The iodine a toms, to which the TPPS molecules are connected, are almost perpendicular a ppendages on opposite sides of each ribbon. Weaker interactions between the ribbons give rise to unprecedented continuous stepped layers of diiodine m olecules anchored to TPPS donor units. The structural features of TPPS . 3I (2) are discussed in comparison with those of the previously reported 2TPPS . 3I(2), TPPS . I-2, TPPS . IBr and TPPS . ICl, and its FT-Raman spectrum compared with those of 2TPPS . 3I(2) and TPPS . I-2. A re-examination of th e equilibrium reaction between TPPS and I-2 by P-31 NMR confirms the format ion of the 1 : 1 adduct in CH2Cl2 solution and gives a formation constant v alue of 137 +/- 11 dm(3) mol(-1).