The host−guest inclusion complexes of cucurbiturils with alkyl viologen have interesting architectures, chemicalproperties, and potential applications in sensors and nanotechnology. A highly hydrated triclinic crystal of cucurbituril (CB) complexed by methyl hexadecyl viologen (MVC16) is characterized by the unprecedented coexistence in the crystal of three host−guest complexes with 3:2, 2:2, and 1:1 stoichiometries. In all these complexes, the hook-shaped alkyl chain of the MVC16 is hosted in the CB macrocycles, while the methyl viologen moieties have various environments. In the Z-shaped 3:2 complex, a central CB unit hosts two viologen heads in the cavity, while the 2:2 complex is held together by π-stacking interactions between two viologen units. In the square 2D tiling crystal packing of CB macrocycles, the same site which favors the dimerization observed in the 2:2 complex is also statistically occupied by a single methyl viologen moiety of the 1:1 complex. The rational interpretation of the crystal structure represented an intriguing challenge, due to the complicated statistical disorder in the alkyl chains hosted in CB units and in the methyl viologen moieties of 2:2 and 1:1 complexes. In contrast with the solution behavior dominated by the 2:1 complex, the coexistence of three host−guest complexes with 3:2, 2:2, and 1:1 ratios highlights the fundamental importance of packing effects in the crystallized supramolecular complexes. Therefore, the crystallization process has permitted us to capture different host−guest systems in a single crystal, revealing a supramolecular landscape in a single photo.
Methyl Hexadecyl Viologen Inclusion in Cucurbituril: Coexistence of Three Host–Guest Complexes with Different Stoichiometry in a Highly Hydrated Crystal / Hickey, Neal; Medagli, Barbara; Pedrini, Alessandro; Pinalli, Roberta; Dalcanale, Enrico; Geremia, Silvano. - In: CRYSTAL GROWTH & DESIGN. - ISSN 1528-7483. - 21:7(2021), pp. 3650-3655. [10.1021/acs.cgd.1c00463]
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