Advanced buckyball joints: synthesis, complex formation and computational simulations of centrohexaindane-extended tribenzotriquinacene receptors for C60 fullerene.

The synthesis of a structurally optimized tribenzotriquinacene receptor 9 is described, which is extended by centrohexaindane moieties to give rise to a half-round concave ball bearing, with optimum shape complementarity towards C(60) fullerene. Spectroscopic investigations reveal that this novel host forms a 1 : 1 host-guest complex with C(60) with a complex stability constant of K(1) = 14,550 ± 867 M(-1), which is considerably higher than those reported for structurally related tribenzotriquinacene hosts reported previously. Both the suppression for binding of a second receptor (i.e. formation of a 2 : 1 host-guest complex) as well as the increase of complex stability of the 1 : 1 complex can be rationalized in terms of multiple additive van der Waals and π-π interactions between C(60) and the aromatic groups of the receptor, as revealed by DFT + D and force-field calculations. Combining results from spectroscopic and theoretical investigations leads to predictions in light of future receptor designs, which--apart from shape complementarity--will have to consider an optimized electronic match (i.e. partial charge transfer) between the receptor and the fullerene host.