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inthesolution(e.g.,solventefects)canhinderthedevelopmentof
finiteassembliesthatexhibitdesignedandfunctionalproperties[3].
In the solid state, the structural integrity of a molecular assembly
will be essentially maintained since the components are largely
prohibited from dissociating back to individual parts. Inasmuch as
thestructureefectsofmultipleequilibriacanhindertheformation
ofmolecularassembliesinsolution,subtleefectsofcrystalpacking
can hinder the formation of discrete molecular assemblies in solids.
Although a variety of supramolecular interactions can be employed
tocontrolthemolecules'organization,finiteassembliesgeneratedin
either the liquid phase or the solid state have been typically designed
using the strength and directionality of hydrogen bonds [3].
HOMODIMER
HETEROMERIC AGGREGATE
H
O
O
N
H
O
O H
O
O
Scheme 7.1
Discrete two-component aggregates in the form of a
carboxylic
acid
homodimer
(left)
and
pyridine
acid
heteromeric complex (right).
Toconfronttheefectsofcrystalpacking,intherecentyears
chemists have applied a synthetic approach based on co-crystals.
Co-crystals are heteromeric, or multicomponent, solids with organic
moleculesassembledincombinationtoafordpropertiesdiferent
than the individual solid components [6]. A co-crystal typically
consists of a target molecule crystallized with a second molecule,
orco-crystalformer(CCF),thatisusedtoinfluencetheproperties
of the target (e.g., solubility). The CCF will interact with the target
via the intermolecular forces that unite the components together.
The use of a CCF to construct a solid is important since the CCF can
competewiththeefectsofcrystalpackingand,indoingso,aidethe
constructionofafunctionalsolidofthetargetmolecule(Scheme7.2).
Co-crystals have been used to construct the assemblies of molecules
based on one-dimensional (1D), 2D, and 3D networks, as well as 0D,
orfinite,structures[6].
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