Ion-Pairing Crystal Polymorphs of Interlocked [2 + 1]-Type Receptor–Anion Complexes

The formation of
a solid-state totally charge-segregated assembly
(polymorph A) of negatively charged layers comprising
[2 + 1]-type Cl– complexes of an arylethynyl-substituted
dipyrrolyldiketone boron complex and positively charged layers of
tetrabutylammonium (TBA) cations has already been reported. The formation
of two new crystalline polymorphs (polymorphs B and C), in addition to polymorph A, is reported in
this study. Both polymorphs B and C formed
charge-by-charge assemblies, and the dihedral angles between two receptor
units in the interlocked complexes depended on the geometries of TBA
cations and the resulting packing structures. Two nonorthogonally
arranged planes induced P- and M-form chiral geometries, providing diverse arrangements of chiral
species according to crystal polymorphs. Furthermore, the stabilities
of the three polymorphs were examined by interfragment interaction
energies, which were calculated by ab initio electronic
structure calculations using the fragment molecular orbital (FMO)
method.