Corannulenes surfaces

The partially hydrogenated ring of dihydtocorannulene constitutes a 1,3-cyclo-hexadiene ring, a system that has been well-studied with respect to its geometry and the conformational preferences of substituents. However, the curvature of the corannulene surface introduces an additional stereochemical factor that makes the conformational analysis especially interesting. 1,3-Cyclohexadiene (23) and 9,10-dihydrophenanthrene (24) serve as models they are structurally similar systems, and their stereochemistry and conformational preferences are well documented in the literature. In both cases, the reduced ring adopts a nonplanar, semi-chair conformation of symmetry. 

From the assemblies of fused five- and six-membered rings identifiable on the surface of 1, corannulene (8) is the smallest fragment that retains a bowl-shaped conformation. However, there are other known hydrocarbons that adopt bowl (or... 

The preceding section indicated the importance of corannulene as the smallest member of the family of bowl-shaped, polynuclear aromatic hydrocarbons modeling the surface of buckminsterfullerene. Surprisingly, despite its obvious significance in relationship to the theory of aromaticity, 8 had not attracted the attention of chemists prior to the first report of its synthesis in 1966." As Barth and Lawton noted ... to the time of our first report, it appears this structure had neither adoriied the jacket or end cover of any book nor served as a symbol of an international symposium. More than that, corannulene does not appear to have been suggested in the chemical literature prior to 1966. 

It is apparent from Table 1 that the cyclohexadiene ring in 1,2-dihydrocorannule-nes is significantly flatter than either 1,3-cyclohexadiene itself or 9,10-dihy-drophenanthrene due to the constriction imposed by the remainder of the bowl-shaped ring system. Nonetheless, the lack of planarity means that substituents at may adopt either pseudoaxial (pa) or pseudoequatorial (pe) positions. However, the surface of the corannulene system is curved, and, unlike 1,3-cyclohexadiene and 9,10-dihydrophenanthrene, neither the two pa positions nor the two pe positions are equivalent. Thus, substituents in 1 -/ -1,2-dihydrocorannulenes may be (1) endo-pseudoaxial (endo-pa), (2) e do-pseudoequatorial (e/ido-pe), (3) exo-pseudoaxial (exo-pa), and (4) exo-pseudoequatorial (exo-pe), where endo and exo are related to concave and convex orientations, respectively. 

Corannulene is the simplest example within the class of polynuclear aromatic compounds with curved surfaces that are related by carbon framework to the i fullerenes. These aromatic hydrocarbons possess bowl-shaped geometries, consist... 

In this article, we report solution ESR spectra of coronene monoanion, to compare with that of corannulene monoanion. Moreover, we present ab initio molecular orbital (MO) calculation on the JT potentials of monoanionic state of corannulene and coronene, and consider the temperature dependence of the ESR spectra based on these results. Furthermore, the analytical JT potential surfaces of corannulene monoanion and coronene monoanion are derived using group theory. 

To elucidate the difference between corannulene and coronene, we will consider JT potential surfaces in the Section 5.4. 

Figure 7 shows the JT surface on the Zs2( 16) mode of corannulene monoanion. Five equivalent minima and five equivalent saddle points can be seen on the surface, since the e2 configuration space has C5v/C = C5v symmetry. 

Fig. 7. (a) Lower Jahn-Teller potential surface of corannulene monoanion on the E2( 0) mode. The energy barrier between the minima is 7.9 meV. (b) The vibrational vectors of the E2 16) mode, the symmetric one (top) and the asymmetric one (bottom). 

Fig. 10. (a) Lower potential surface of corannulene monoanion using equation (24), (b) cross-section along 0 = 0.0, and (c) cross-section along p = 0.06. 

For the corannulene anion, the quadratic vibronic interaction is vanishing due to its symmetry, and it is necessary to include the fifth-order vibrational anharmonicity and fourth-order vibronic interaction to explain the five equivalent minima. For coronene, on the other hand, if the quadratic vibronic interaction is considered, the interaction gives rise to three minima on the JT surface of the coronene anion. However, this is not the case. It is necessary for the sixth-order vibrational anharmonicity and fourth-order nonlinear vibronic interaction to give rise to the six equivalent minima. 

The metastable, 2-D packing motif presented by some Pcs adsorbed on Ag(l 11) has also prompted the utilization of such ensembles as templates for the organization of complementary guest molecules such as fullerenes [193] or corannulenes [194], giving rise to the formation of two-component, 2-D architectures. More recently, a similar approach has been used to prepare a surface-supported, three-component system. In fact, the immersion of an Au substrate into a solution containing both a ZnPc and a Zn porphyrin led to the formation of a highly ordered, 2-D arrangement of both Pc and porphyrin which can act as a bimolecular chessboard toward the supramolecular assembly of a third component (i.e., C6o fullerene) which is selectively trapped in the open spaces (Fig. 25) [195],... 

The POAV pyramidalization angle of the carbon on the central five-membered ring (hub) in corannulene is 8.2°, in contrast to 11.6° for Ceo. The rim carbons are predicted to be only slightly pyramidalized with pyramidalization angles in the range of 1-2°. Unlike the crystal structures of pyrene and related aromatic compounds of comparable surface area, the crystal structure of 1 is void of any aromatic face-to-face or bowl stacking. However, a mixture of corannulene and fullerene Ceo forms cocrystals [l-Ceo] [66]. The shortest distances from Ceo to the concave surface of 1 and the convex surface of another 1 were determined to be 3.75 and 3.21 A, respectively. 

Transition-metal complex of n bowls have attracted much attention [12, 34, 35]. Controlled positioning of metal centers inside the bowls is expected to provide a direct route to the inclusion complexes of fiillerenes and nanotubes. On the other hand, the coordination of metal centers to the outside of the bowls should permit applications in the field of surface activation and functionalization of fiiUerenes and nanotubes. To date, some n bowl (mainly corannulene or its derivatives) complexes with several coordination modes have been synthesized [12, 34, 35]. In addition to the conventional liquid phase synthesis, a microscale gas-phase coordination method was introduced [36] to prepare and/or jj -binding complexes, which is based on co-deposition of volatile complementary building units such as Rh2(02CCF3)4, Ru2(02C(3,5-CF3)2C H3)2(C0)5, and Ru2(02CCF3)2(C0)4 under reduced pressure. 

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