Dominant cation-cation supramolecular motifs in crystals. Hexagonal arrays of sextuple phenyl embraces in halometalate salts of MePh3P+

The crystal structures of five compounds with phosphonium cations and bromocadmate anions have been determined, and analysed in terms of the supramolecular interactions which determine the lattice types. The salts [MePh3P](2)[CdBr4] and [MePh3P](2)[CdBr4]. CH2Cl2 crystallise in a targe rhombohedral lattice in which dimers of cations in sextuple phenyl embraces (SPE) form a pseudo-diamondoid array, with the anions (and CH2Cl2) contained in cavities surrounded by 12 cations. The same hexagonal array of sextuply embracing cations occurs also in [MePh3P](2)[CdI4] and [MePh3P](2)[Cu4I6], with the dimensions of the array of cations quite variable according to the size and shape of the anion. This newly recognised lattice type (HASPE, hexagonal array of sextuple phenyl embraces) is maintained principally by the strongly attractive SPEs and by attraction between the anion and surrounding cations. The HASPE is a crystal structure type with general occurrence. The cations in the crystal structures of [Ph4P](2)[CdBr4] and [Ph4P](2)[Cd2Br6] occur as zigzag infinite sextuple phenyl embraces (ZZISPEs), chains of cations which are orthogonal and parallel respectively. Determination of the crystal structure of [HPh3P](2)[CdBr4] reveals an absence of specific cation-cation interactions.