Soft-soft interations involving iodoselenophosphonium cations: supramolecular structures of iodine adducts of bulky trialkylphosphane selenides

The reactions of trialkylphosphane selenides tBuniPr3–nPSe (n = 3: 1a; n = 2: 1b; n = 1: 1c; n = 0: 1d) with iodine are studied with the help of heteronuclear NMR spectroscopy, vibrational spectroscopy, and X-ray crystal structure determinations. The reaction of 1a with one equivalent of iodine provides, after crystallization from dichloromethane/pentane, solid 2a, which consists of pairs of molecular adducts tBu3PSe–I–I, together with chains of alternating [(tBu3PSe)2I]+ and I3 – ions. The addition of iodine to 1b, 1c, and 1d in a 1:1 molar ratio furnishes ionic solids with the formulation [(tBuniPr3– nPSe)2I]+[I3]– (n = 2: 2b; n = 1: 2c; n = 0: 2d). Compounds 2a–2d exhibit supramolecular structures based on various kinds of weak Se···I and Se···Se interactions. In 2a, the uncharged molecules form dimers through Se···Se contacts, while the anions and cations assemble to form chains through linear P–Se···Ianion contacts. The ionic compounds 2b and 2d consist of the same type of chains, although they are not isotypic to each other. The two independent formula units of 2c are topologically different; one forms cation–anion chains analogous to those of 2b and 2d, whereas the other forms cation chains through Se···Se contacts. Se···I contacts between the latter chains and triiodide anions are very long but seem to be structurally significant; for such contacts, at well above the sum of the van der Waals radii, we propose the term tertiary contacts. On using more than one equivalent of I2, compounds corresponding to the formulation tBuniPr3– nPSeIx (x = 3, n = 3: 3a; x = 4, n = 1: 4c; x = 7, n = 2 and 0: 5b and 5d) were isolated as single crystals. Ionic 3a contains pairs of cations [(tBu3PSe)2I]+, connected by Se···Se contacts, located between corrugated layers of polymeric I5 – anions. Compound 4c consists of two independent formula units tBuiPr2PSeI2·I2, which could, however, be regarded as tBuiPr2PSeI+·I–·I2 because of the long I–I distance adjacent to Se. To a fair approximation, the packing of the two units is independent; unit 1 forms dimers (···Se–I–I···I–I···)2, whereas the same motif in unit 2 forms chains. The structural subunits are linked through further contacts involving terminal iodine atoms from tBuiPr2PSeI···I units, which thereby form μ3- bridging units, and by additional I–I···Se contacts. In 5b, iodide-bridged cations [tBu2iPrPSeI···I···ISePiPrtBu2]+ are anchored to a polyiodide network of formal composition I11 – [= (I–)(I2)5] through I···I contacts. Except for one I···I contact, the polyiodide is two-dimensional, although highly puckered. In 5d, [iPr3PSeI]+ cations and I2 molecules exhibit weak I···I interactions with I– units from puckered square-net-like polyiodide layers.