Halogen Bonding in Crystal Engineering - Halogen Bonding: Fundamentals and Applications - page 105

DBTFB Dibromotetrafluorobenzene
DIB Diiodobenzene
DITFB Diiodotetrafluorobenzene
HB Hydrogen bonding
HMTA Hexamethylenetetramine
PFC Perfluorocarbon
TIE Tetraiodoethylene
TMEDA Tetramethylethylenediamine
XB Halogen bonding

1
Introduction

Following the concept introduced by Jean-Marie Lehn in 1978, supramolecu-
lar chemistry can be considered as “... the chemistry of molecular assem-
blies and of the intermolecular bond” [1]. This concept encompasses several
poorly related disciplines, both within chemistry and at the interface of chem-
istry with condensed matter physics, materials science, and biology. This
chapter will have a more specific focus on some of these topics and we will
focus on crystal engineering involving organic compounds, a subject of the
diversified topics addressed by supramolecular chemistry. Moving from the
paradigm shift [2] that supramolecular chemistry generated from the focus
on atoms and the bonds between atoms, to the focus on molecules and bonds
between molecules, in this chapter we will concentrate on the atomic charac-
teristics conferring to molecules, or to molecular sites, the specific properties
that determine their mutual complementarity via halogen bonding.
Intermolecular recognition and self-assembly processes both in the solid,
liquid, and gas phases are the result of the balanced action of steric and
electronic factors related to shape complementarity, size compatibility, and
specific anisotropic interactions. Rather than pursuing specific and defini-
tive rules for recognition and self-assembly processes, we will afford some
heuristic principles that can be used as guidelines in XB-based supramolecu-
lar chemistry.
The term halogen bonding (XB) [3-8] indicates any D X-Y interaction

in which X is the electrophilic halogen (Lewis acid, XB donor), D is a donor
of electron density (Lewis base, XB acceptor), and Y is carbon, nitrogen, halo-
gen, etc. (Fig. 1).
Most of the energetic or geometric trends found in hydrogen-bonded com-
plexes (wherein hydrogen functions as the acceptor of electron density) and
other interaction features known from spectroscopic or theoretical investi-
gations are encountered in halogen-bonded complexes as well [9-12]. Ex-
pectedly, halogen atoms being much larger than hydrogen atoms, XB is more
sensitive to steric hindrance than hydrogen bonding (HB) [13].

···