Halogen Bonding in Crystal Engineering - Halogen Bonding: Fundamentals and Applications - page 121

CBr 4 / N , N , N , N -tetramethyl- p -phenylendiamine [134], CBr 4 /4,4 -bis( N , N -
dimethylaminophenyl)methane [134], CHBr 3 /HMTA [173], CHBr 3 /1,4-di-
methoxybenzene [134], 1,4-DITFB/TMEDA 3 , and other systems [64, 134, 147,
174-177]).
When halide anions are used as electron donors, they frequently work
as bidentate modules with either linear or angled geometries. Thus, on
interaction with bidentate XB donors, linear [83, 178, 179] or herringbone
chains [57, 90, 92, 155, 180-185] are formed.
When the binding sites are conveniently pre-organized on the start-
ing modules, topologies that recall 1D infinite chains are formed, also
starting from polydentate modules. This is the case, for instance, of the
ribbons [186, 187] given by a tetradentate module (where interactions

point the four arms two by two to opposite sides of the core), and the nanopil-
lars [188] given by an hexadentate module (where a phosphazene scaffold
directs the six pendants three by three to the opposite sides of the phosp-
hazene ring). In both cases a linear bidentate partner works as connector
of the polydentate modules and translates the polydentate module geometry
into the supramolecular architecture geometry.

π - π

3.2
2D Architectures

When one, or both, the interactive modules are tridentate, bidimensional
(2D) architectures can be formed. A frequently recurring pattern is the (6,3)
network (honeycomb structure), which is sometimes formed when onium
halides self-assemble with dihalocarbons. Halide anions work as tridentate
XB acceptors and occupy the nodes while the dihalocarbons work as biden-
tate XB donors and form the sides that space the nodes. Such architectures are
present in the co-crystals 1,4-DITFB/Ph 4 P + Br - ,1,4-DITFB/Me 4 N + I -

[155],

and KI [128, 189]. The less planar the

trigonal arrangement around the nodes, the more corrugated the honeycomb
structure (Fig. 9).
The same (6,3) topology can be formed on self-assembly of tridentate
XB donors with tridentate XB acceptors. After this self-assembly paradigm,
the complementary partners alternate at the nodes of the 2D architec-
ture. Examples are the co-crystals CHI 3 /HMTA [190], CHI 3 /Ph 4 P + Cl - [183],
CHI 3 /BnMe 3 N + I - [191], CBr 4 / n -Bu 4 N + Br - [192], and CBr 4 / n -Bu 4 N + SCN -
[134]. In these structures the halomethane molecules obviously have a tetra-
hedral geometry and the XB linearity translates the pyramidal arrangement
of these tectons, which sit at the nodes of the network, into the corrugation of
the honeycomb structure (Fig. 10).

α , ω -diiodoperfluoroalkanes/K.2.2.2. ⊂

3 M. Bolte, private communication, CCDC structure reference code QIHCOZ01