High symmetry crystal supramolecularity: –XPh3 molecules in rhombohedral lattices, using multimolecular rather than bimolecular sixfold phenyl embraces

Abstract

Molecules of the type Ph₃XYXPh₃ commonly crystallise in trigonal and rhombohedral lattices comprised of hexagonal arrays of sixfold phenyl embraces (HA6PE) which are bimolecular concerts of edge-to-face (EF) phenyl···phenyl interactions. In this paper we describe crystal structures containing molecules Ph₃XYXPh₃, also crystallising in the space group R characteristic of the HA6PE lattice, but without the bimolecular (EF)₆ form of 6PE. Instead there are multimolecular concerts of EF and offset-face-to-face (OFF) motifs, building up hexagonal layers and in some cases generating high symmetry cavities. These crystals possess the same molecular symmetry as the HA6PE systems, and crystallise in the same space groups, but have different intermolecular motifs: they are effectively crystal supramolecular isomers of the HA6PE lattice. The specific crystalline compounds analysed are Ph₃SiOSiPh₃·C₆H₆, Ph₃SiNCNSiPh₃ and Ph₃PNPPh₃⁺[Nb(CO)₆]⁻. The crystal packing in (MePh₃P)₂[Cu₄I₆], and in a high symmetry Ni₃ complex crystallised with Ph₃PO, both in space group Rc also characteristic of the HA6PE lattice, are supramolecular isomers of the HA6PE lattice because the bimolecular motif is (OFF)₃ rather than (EF)₆. The crystal packing analyses benefit by recognition of the asymmetric sectors of the intermolecular interactions and of cavities, in addition to the conventional asymmetric sectors of the molecular components.