title: The origin of the room-temperature stability of [TTF]˙⁺⋅⋅⋅[TTF]˙⁺ long, multicenter bonds found in functionalized π-[R-TTF]₂²⁺ dimers included in the cucurbit[8]uril cavity.
abstract: A computational study is performed to identify the origin of the room-temperature stability, in aqueous solution, of functionalized π-[R-TTF]2(2+) dimers (TTF=tetrathiafulvalene; R=(CH2OCH2)5CH2OH) included in the cavity of a cucurbit[8]uril (CB[8]) molecule. π-[R-TTF]2(2+) dimers in pure water are weakly stable, and are mostly dissociated at room temperature. Upon addition of CB[8] to an aqueous π-[R-TTF]2(2+) solution, a (π-[R-TTF]2⊂CB[8])(2+) inclusion complex is formed. The same complex is obtained after the sequential inclusion of two [R-TTF](.+) monomers in the CB[8] molecule. Both processes are thermodynamically and kinetically allowed. π-[R-TTF]2(2+) dimers dissolved in pure water present a [TTF](.+)⋅⋅⋅[TTF](.+) long, multicenter bond, similar to that already identified in π-[TTF]2(2+) dimers dissolved in organic solvents. Upon their inclusion in CB[8], the strength and other features of the [TTF](.+)⋅⋅⋅[TTF](.+) long, multicenter bond are preserved. The room temperature stability of the π-[R-TTF]2(2+) dimers included in CB[8] is shown to originate in the π-[R-TTF]2(2+)⋅⋅⋅CB[8] interaction, the strength of which comes from a strongly attractive electrostatic component and a dispersion component. Such a dominant electrostatic term is caused by the strongly polarized charge distribution in CB[8], the geometrical complementarity of the π-[R-TTF]2(2+) and CB[8] geometries, and the amplifying effect of the 2+ charge in π-[R-TTF]2(2+).
authors.affiliation: Departament de Química Física and IQTCUB, Facultat de Química, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona (Spain).
authors.forename: Marçal
authors.initials: M
authors.lastname: Capdevila-Cortada
authors.forename: Joel S
authors.initials: JS
authors.lastname: Miller
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Novoa
keywords: density functional calculations; dimerization; host-guest systems; inclusion compounds; supramolecular chemistry