“Texas-Sized” Molecular Boxes: Building Blocks for the Construction of Anion-Induced Supramolecular Species via Self-Assembly

It
was previously established that the flexible tetraimidazolium
macrocycle cyclo[2]­(2,6-bis­(1H-imidazol-1-yl)­pyridine)­[2]­(1,4-dimethylenebenzene)
(14+) is capable of stabilizing higher-order
supramolecular structures via both anion and cation recognition. Described
herein is a set of structurally related imidazolium macrocycles (24+–44+) that contain
modified central cores. The flexible nature of these new constructs
is highlighted by the isolation of several independent crystalline
forms for the same basic structure. Each of the individual receptors
was found to bind the 2,6-naphthalenedicarboxylate dianion and to
stabilize the formation of self-associated structures. The observed
binding modes and resulting supramolecular organizational forms were
found to differ dramatically depending on the nature of the bridging
group present in the imidazolium macrocycle. This finding was established
by solution studies involving, inter alia, one- and two-dimensional
(1H, 1H–1H COSY, DOSY, and
NOESY) NMR spectroscopy as well as electrospray ionization mass spectrometry.
The new systems in this report serve to expand the available “tool
box” for the construction of complex self-assembled materials
while providing insights into the determinants that regulate the formation
of specific supramolecular structures from flexible receptors capable
of adopting multiple stable conformations.