The nanoscale host-guest interactions between [n]cycloparaphenylene ([n]CPP; n = 10, 8 and 9) nano-ring and fullerene C60 were explored theoretically. It is found that relatively small variations in the sizes of the [n]CPP host lead to very significant changes in encapsulation property toward the fullerene C60 guest. Expectedly, one stable inclusion-configuration of [10]CPP⊃C60 and one floating-configuration of [8]CPP⊃C60 are located on the potential surfaces of the two complexes, respectively. Unexpectedly, besides a floating-configuration (F-[9]CPP⊃C60), another stable inclusion-configuration (I-[9]CPP⊃C60) is also located on the potential surface of [9]CPP⊃C60 host-guest complex. Interaction energies and natural steric analysis show that these complexes are stabilized by balancing concave-convex π-π attractive and steric repulsive host-guest interactions. In contrast, the steric repulsive energy (Es) between host and guest of I-[9]CPP⊃C60 is as high as 233.12 kJ mol(-1), which is much larger than those in other complexes. The movements of C60 guest through the cavities of [n]CPP host (n = 10, 8 and 9) are simulated by calculating the energy profile, and the results interestingly reveal that the encapsulation of C60 by [10]CPP is in the manner of a single-potential well, by [8]CPP in the manner of a double-potential well, and by [9]CPP in the special manner of a three-potential well. We predict that the movement of C60 guest through the cavity of [9]CPP host should be experimentally observable owing to the relatively low energy barrier (<50 kJ mol(-1), M06-2X/6-31G(d)). Charge population analysis shows that an obvious charge transfer between host and guest takes place during the formation of I-[9]CPP⊃C60, which is different from those during the formation of [8]CPP⊃C60, [10]CPP⊃C60 and F-[9]CPP⊃C60. Additionally, the host-guest interaction regions were detected and visualized in real space based on the electron density and reduced density gradient.

With a combined methodology of quantum chemistry and statistical mechanics, two Yb@C 76 isomers are disclosed to possess novel fullerene structures which contain one pair of adjacent pentagons and are related by a single Stone-Wales transformation.Fullerenes synthesized to date satisfy the isolated-pentagon rule (IPR), which states that each pentagon on a fullerene cage should be surrounded by hexagons in a stable fullerene isomer. 1,2 However, non-IPR fullerene cages with abutting pentagons are also attractive not only because of their unique structures, but also owing to their unusual properties resulting from the high curvatures around the adjacent pentagons. 3 These pure-carbon non-IPR fullerenes are always unstable and synthetically unattainable in the experiments, due to enhanced steric strain (steric effect) and resonance destabilization pertaining to the pentalene-type 8p-electron system (electronic effect). 4 Fortunately, through exohedral derivatization or endohedral metal-doping, such non-IPR fullerene cages can be successfully synthesized and isolated. 5,6 These fullerenes with endohedral metaldoping are commonly called endohedral metallofullerenes (EMFs).Since the cage 19150:D 2 -C 76 was identified as the first higher fullerene except C 60 and C 70 , C 76 fullerenes are viewed as a peculiar species and have attracted lots of interest. 2,7 Among 19151 classical fullerene isomers of C 76 , there are only two IPR-satisfying structures available. One IPR cage (19150:D 2 ) 2 is a small chiral IPR fullerene which can be obtained as the pristine fullerene as well as in the form of Sc 2 @C 76 . 7 Another IPR cage (19151:T d ) is the higher symmetry fullerene cage which can be generated and stabilized as Lu 2 @C 76 because electrons transfer from the lutetium atoms to the fullerene cage when encapsulating two Lu atoms. 8 The only non-IPR cage example of C 76 -based EMFs is the mixed metal nitride cluster fullerene, DySc 2 N@C 76 , which was predicted to possess the 17490:C s cage with two pairs of pentagon adjacencies. 9 On the other hand, several species of C 76 -based mono-EMFs, M@C 76 , with divalent M (M ¼ Ca, Sr, Sm, Yb) have been synthesized and isolated. 10 These mono-EMFs usually have more than one isomer, which provides additional opportunities for investigating the metal-cage interactions, physical and chemical properties, and potential applications of EMFs. 11 The diverse isomerism of the divalent EMFs also makes it possible to study the effect of the cage on the electronic structures and properties of the EMFs. However, to our best knowledge, neither experimental nor theoretical effort has been paid upon the cage structures of C 76 -based monoEMFs up to now.Here we report that by combined quantum chemical and statistical thermodynamic methods, two new Yb@C 76 isomers are disclosed to possess non-IPR cage structures, both of them have one pair of pentagon adjacencies and are related by a single Stone-Wales transformation. Moreover, the electronic structures, ionization energies, electron affinitie...

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