IntroductionThe sixfold phenyl embrace (6PE) is an established intermolecular motif occurring between XPh3groups in a variety of molecules.1–5The 6PE is comprised of a set of six phenyl rings engaged in a cycle of six concerted edge­to­face (EF) local interactions between phenyl groups and is commonly centrosymmetric. The 6PE is widespread in crystals containing the Ph4P+cation,3,6–8in metal complexes containing PPh3ligands,2,9–11and in the structures of diverse molecules like Ph3ER with molecularC3symmetry.12,13Here, we describe and analyse the crystal packing and supramolecularity of molecules Ph3XSnXPh3where two XPh3groups occur at the ends of a simple flexible polysulfane chain Sn. These differ from previous instances of molecules with two or more XPh3groups where the intramolecular geometry restricts the directions of the XPh3groups, as, for example, in orthogonal M(PPh3)2moieties (cisandtrans), and trigonal M(PPh3)3.11Polysulfane chains provide conformationally variable linkages, and use the minimum number of atoms needed for a connecting chain. Unlike most other systems, molecules Ph3XSnXPh3contain low­volume and flexible connectors between XPh3groups. Furthermore, molecules Ph3XSnXPh3are chemically simple, and allow only two types of intermolecular interaction – S⋯Ph3X and S⋯S – in addition to multiple phenyl embraces. This simplicity of atom type is important for the purpose of unravelling and assessing the relative influences of supramolecular motifs.A search of the Cambridge Structural Database14,15(CSD) (version 5.20, October 2000) for structures of the type Ph3XSnXPh3(where X⊕=⊕any non­P atom) revealed 11 examples. These, together with the new crystal structure for Ph3CS3CPh3reported here, are listed with cell dimensions and space groups inTable 1. Only one crystal (refcode YAVDAA, Ph3CS5CPh3·CHCl316) includes solvent, and the general non­occurrence of solvent in this set of 12 crystals is an indication of efficient crystal packing.Crystal structures for compounds of the class Ph3XSnXPh3nXSource (REFCODE)Space groupCell dimensionsa,b,c/Å(α), (β), (γ)/°This structure has also been determined at −130 °C (DTPGES).There are three entries for this structure in the CSD.Includes disordered chloroform in the lattice.161CPHMESFP1&cmb.macr;8.83, 9.47, 17.5990.15, 92.58, 106.581SiDEBYAKP21/n17.08, 14.55, 12.2597.271GeDTPGES02P21/c11.08, 15.71, 18.81107.291GeDTPGES01P2121219.62, 17.35, 18.41—1SnTPSNSLP21212118.50, 17.62, 9.81—2CPEKZAGP21/c13.94, 12.10, 17.30103.633C1, this workP21/c13.92, 12.79, 20.68124.393GeCAFFAQP21/n11.97, 17.98, 16.74100.374SiWEYHOXP1&cmb.macr;9.44, 9.46, 18.8282.11, 78.95, 83.155CYAVDAAP21/n8.76, 16.97, 25.2395.406CYAVDEEP1&cmb.macr;9.52, 10.33, 18.5485.78, 80.04, 67.45Table 1reveals the occurrence of polymorphism – crystal packing isomerism – which is also a valuable phenomenon in understanding crystal supramolecularity. Ph3GeSGePh3crystallises in two different lattices, as conventional dimorphs. However, the polymorphism of the Ph3XSnXPh3set of crystals also involves molecules with internal homologous substitution, and is an extension of the conventional view of polymorphism as crystal isomers of the same molecule.17–23In the Ph3XSnXPh3set of compounds the atom X is C, Si, Ge or Sn, varying only in size and not stereochemistry, and this variation occurs inside the surface of the molecule and does not directly influence the intermolecular interactions. This substitutional polymorphism is analogous to the ‘iso­electronic’polymorphism described by Braga and Grepioni for variation of metal,24and illustrates the need for a wider perspective of polymorphism in inorganic contexts.25In the current collection of compounds there are four molecules Ph3XSXPh3with X⊕=⊕C, Si, Ge, Sn, with four different crystal lattices (Table 1): these are substitutional polymorphs. Further, there are two molecules Ph3XS3XPh3with X⊕=⊕C, Ge, and with different crystal lattices. The question that arises here is whether these subtle internal molecular differences are sufficient to cause distinctly different crystal packing. This bears on a fundamental issue in the fields of crystal supramolecularity, crystal structure prediction, and crystal engineering, namely the relative influences of (1) the energy wells in thepotential energy surface for molecular configurations and (2) the energy wells in the potential energy surface for crystal packing.Previous investigations of intermolecular interactions involving S atoms in molecular crystals have focussed on statistical analyses of S⋯S metrical properties in crystals, looking at the environs of individual surface S functions.26–30In order to investigate the fundamental issues mentioned in the previous paragraph we analyse the full crystal packing for the compounds to be described, and we calculate some relevant intermolecular energies.