Capdevila-Cortada Marçal, Miller Joel S, Novoa Juan J
Departament de Química Física and IQTCUB, Facultat de Química, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona (Spain).
Chemistry. 2014 Jun 16;20(25):7784-95. doi: 10.1002/chem.201402256. Epub 2014 May 26.
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+).
开展了一项计算研究，以确定包含在葫芦[8]脲（CB[8]）分子空腔中的功能化π-[R-TTF]2(2+)二聚体（TTF = 四硫富瓦烯；R = (CH2OCH2)5CH2OH）在水溶液中室温稳定性的来源。纯水中的π-[R-TTF]2(2+)二聚体稳定性较弱，在室温下大多解离。向π-[R-TTF]2(2+)水溶液中加入CB[8]后，会形成(π-[R-TTF]2⊂CB[8])(2+)包合物。在CB[8]分子中依次包合两个R-TTF单体后也能得到相同的配合物。这两个过程在热力学和动力学上都是可行的。溶解在纯水中的π-[R-TTF]2(2+)二聚体呈现出TTF⋅⋅⋅TTF长程多中心键，类似于已在溶解于有机溶剂中的π-[TTF]2(2+)二聚体中鉴定出的那种键。当它们被包合在CB[8]中时，TTF⋅⋅⋅TTF长程多中心键的强度和其他特征得以保留。结果表明，包含在CB[8]中的π-[R-TTF]2(2+)二聚体的室温稳定性源于π-[R-TTF]2(2+)⋅⋅⋅CB[8]相互作用，其强度来自强吸引性的静电成分和色散成分。这种占主导地位的静电项是由CB[8]中强烈极化的电荷分布、π-[R-TTF]2(2+)与CB[8]几何形状的几何互补性以及π-[R-TTF]2(2+)中2+电荷的放大效应引起的。
