Computational characterization and modeling of buckyball tweezers: density functional study of concave-convex pi center dot center dot center dot pi interactions

The geometries and binding energies of a recent buckyball tweezers (C60H28) and its supramolecular complexes are investigated using recently developed density functionals (M06-L and M06-2X) that include an accurate treatment of medium-range correlation energy. The pincer part of the tweezers, corannulene, has a strong attractive interaction with C-60. However, due to the entropy penalty, the calculated gas-phase free energy of association of the C-60@ corannulene supramolecule is positive 3.5 kcal mol(-1); and this entropy penalty explains why it is difficult to observe C-60@ corannulene supramolecule experimentally. By using a pi-extended tetrathiafulvalene (TTF), in particular 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ or C20H10S4), as the pincer part, we modeled a new buckyball tweezers. The geometries and binding energies of the new buckyball tweezers and its supramolecular complexes are also calculated. Due to fact that the attractive interaction between TTFAQ and C-60 is weaker than that between corannulene and C-60, the gas-phase binding free energy in the C-60@ C60H S-32(8) supramolecular complex is smaller than that in the C-60@C60H28 supramolecule. We also discuss solvent effects.