Emergent Self-Assembly of a Multicomponent Capsule via Iodine Capture

Described
here is a three-component self-assembly system that displays
emergent behavior that differs from that of its constituents. The
system comprises an all-hydrocarbon octaaryl macrocycle cyclo[8]­(1,3-(4,6-dimethyl)­benzene
(D4d-CDMB-8),
corannulene (Cora), and I2. No appreciable
interaction is seen between any pair of these three-components, either
in cyclohexane or under various crystallization conditions. On the
other hand, when all three-components are mixed in cyclohexane and
allowed to undergo crystallization, a supramolecular iodine-containing
capsule, ((D4d-CDMB-8)3⊃(Cora)2)⊃I2, is obtained. This all-hydrocarbon capsule
consists of three D4d-CDMB-8 and two Cora subunits and contains a
centrally bound I2 molecule as inferred from single-crystal
and powder X-ray diffraction studies as well as solid-state 13C NMR and Raman spectroscopy. These analyses were complemented by
solution-phase 1H NMR and UV–vis spectroscopic studies.
No evidence of I2 escape from the capsule is seen, even
at high temperatures (e.g., up to 418 K). The bound I2 is
likewise protected from reaction with alkali or standard reductants
in aqueous solution (e.g., saturated NaOH­(aq) or aqueous Na2S2O3). It was also found that a mixed powder
containing D4d-CDMB-8 and Cora in a 3:2 molar ratio could capture saturated
I2 vapor or iodine from aqueous sources (e.g., 1.0 mM I2 in NaCl (35 wt %) or I2 + NaI­(aq) (1.0 mM each)).
The present system displays structural and functional features that
go beyond what would be expected on the basis of a simple sum-of-the-components
analysis. As such, it illustrates a new approach to creating self-assembled
ensembles with emergent features.