Dominant cation–cation supramolecular motifs in crystals. Hexagonal arrays of sextuple phenyl embraces in halometalate salts of MePh3P+
Abstract
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
[MePh
3
P]
2
[CdBr
4
] and
[MePh
3
P]
2
[CdBr
4
]·CH
2
Cl
2
crystallise in a large rhombohedral lattice in which
dimers of cations in sextuple phenyl embraces (SPE) form a
pseudo-diamondoid array, with the anions (and
CH
2
Cl
2
) contained in cavities surrounded by 12
cations. The same hexagonal array of sextuply embracing cations occurs
also in [MePh
3
P]
2
[CdI
4
] and
[MePh
3
P]
2
[Cu
4
I
6
], 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
[Ph
4
P]
2
[CdBr
4
] and
[Ph
4
P]
2
[Cd
2
Br
6
] occur as
zigzag infinite sextuple phenyl embraces (ZZISPEs), chains of cations
which are orthogonal and parallel respectively. Determination of the
crystal structure of [HPh
3
P]
2
[CdBr
4
]
reveals an absence of specific cation–cation interactions.
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