title: Mining 2:2 Complexes from 1:1 Stoichiometry: Formation of Cucurbit[8]uril-Diarylviologen Quaternary Complexes Favored by Electron-Donating Substituents.
abstract: A 1:1 binding stoichiometry of a host-guest complex need not consist of a single host and guest. Diarylviologens containing electron-donating substituents complexed with cucurbit[8]uril (CB[8]) in a 1:1 stoichiometry exhibit abnormally large binding enthalpies compared to typical enthalpy changes observed for 1:1 binary complexes. Here, several CB[8]-mediated host-guest complexes, which were previously reported as 1:1 binary complexes, are verified to be 2:2 quaternary complexes by a combination of isothermal titration calorimetry,1H, NOESY, and ROESY NMR, and ion mobility mass spectrometry, clearly indicating a binding motif of two partially overlapping diarylviologens held in place with two CB[8] molecules. Formation of 2:2 quaternary complexes is favored by electron-donating substituents, while electron-withdrawing substituents typically result in 1:1 binary complexes. The stacking of two highly conjugated diarylviologens in one quaternary motif affords the complexes enhanced conductance when considered as a single-molecular conductor. Moreover, an additional conducting signal previously observed for this "supramolecular" conductor can be readily understood with our 2:2 complexation model, corresponding to a parallel conductance pathway. Therefore, a 2:2 quaternary complex model grants a greater understanding of such supramolecular complexes, enabling the design of engineered, hierarchical structures and functional materials.
authors.affiliation: Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Guanglu
authors.initials: G
authors.lastname: Wu
authors.affiliation: Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Olesińska
authors.affiliation: Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Yuchao
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Dijana
authors.initials: D
authors.lastname: Matak-Vinkovic
authors.affiliation: Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Oren A
authors.identifier: 0000-0001-8032-7166
authors.initials: OA
authors.lastname: Scherman