Dual modification to stabilize Non-IPR C72 fullerene: A new theoretical strategy

The stabilization of non-IPR fullerenes for their isolation and characterization is an area of recent interest. In the present study, we have explored the stabilization techniques of C₇₂ isomers via endo and exo-modifications and finally approached dual modification. A total of four isomers of C₇₂ have been considered in this study; among them, one is IPR derivative (1), and the rest are non-IPR derivatives with one (2) and two (3 and 4) fused pentagon rings. First, we have studied the endohedral modification by encapsulating one and two La atoms in the C₇₂ cavity. Secondly, we have exohedrally modified the C₇₂ isomers via chlorination by adding four and eight chlorides, respectively. Our final approach is to study the dual modification, where we have implemented both endo exo-modifications together. This dual modification can be achieved in two ways: exo followed by endo and endo followed by exo. For each modification, the relative stability of every modified C₇₂ derivative has been checked by calculating the relative energy with respect to the most stable modified analogue. To find out whether these modifications are energetically feasible or not, we have calculated the binding energy of each modified C₇₂ isomer. The binding energy calculation reveals that the encapsulation and exo-modification techniques are good enough to stabilize the non-IPR C₇₂ derivatives. Moreover, the effectiveness of dual modification has also been established from the enhanced binding energy compared to either endo- or exo-modification. We have also studied the NPA charges on the encapsulated La atoms for each endo- and dual-modified C₇₂ derivative. Furthermore, the AIM study has also been perceived to find out the interaction between the La atom and the fullerene cages for both mono- and di-encapsulated fullerene derivatives and also between La-La centres for di-encapsulated derivatives. Overall, the present theoretical study will provide an idea about the stability of the modified C₇₂ derivatives, which will help the experimentalists to design new strategies for synthesizing modified non-IPR fullerene derivatives that have vast applications in the medicinal and industrial fields.

Dehydrogenation of ammonia-borane to functionalize neutral and Li+-encapsulated C60, C70 and C36 fullerene cages: a DFT approach

Mechanistic investigations into the functionalization of three fullerene cages, viz. C₆₀, C₇₀, and C₃₆ through dehydrogenation of ammonia-borane (AB) have been conducted using Density Functional Theory (DFT). In this process of functionalization, different ring fusions, namely (6-6), (6-5) positions for C₆₀ and C₇₀, and an additional (5-5) for C₃₆ fullerene have been investigated. The optimized geometries of all the complexes and transition states have been characterized using the M06-2X functional in conjunction with the 6-31G(d) basis set. The effect of Li⁺-encapsulation on the energetics and activation barriers of H₂ attachment has also been examined. Although the process of functionalization of neutral fullerenes proceeds extensively through concerted pathways, a step-wise route has been observed for the encapsulated systems. NPA charge analysis and Wiberg bond index (WBI) have been used in order to detect the change in the nature of participating hydrogen atoms and validate the variation in the bond order of the C-C connectivity respectively upon hydrogenation. GCRD parameters have also been calculated to explicate the electronic properties of the hydrogenated products. The (6-6) hydrogenation is observed to be favoured thermodynamically and kinetically for both neutral and Li⁺-encapsulated C₆₀ and C₇₀, while (5-5) is found to be the most preferred site for C₃₆ systems. Our theoretical exploration suggests that the covalent functionalization of the fullerene cages can be done successfully viaAB resulting in the stabilization of these systems. In short, the present work will provide a general idea about the detailed mechanism related to the functionalization of fullerene cages, which will further motivate researchers in fullerene chemistry.

Covalent interactions depend on the distances between metals and fullerenes for thermodynamically stable M@C78 (M = La, Ce, and Sm)

Thermodynamic selectivity occurs between fullerenes and metals in M@C₇₈ (M = La, Ce, Sm), including non-IPR C₁(22 595)-C₇₈; the different number of electrons transferred from metals to C₇₈ leads to the first EMF with diradical features.

Strain Release of Fused Pentagons in Fullerene Cages by Chemical Functionalization

According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused-pentagon-containing (i.e. non-IPR) fullerenes through an exhaustive review of all the types of fused-pentagon-containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in-depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.

The inner-induced effects of YCN in C76 on the structures and nonlinear optical properties

Very recently, an unprecedented novel monometallic cluster of fullerenes entrapping a yttrium cyanide (YCN) cluster inside a popular C82 cage YCN@Cs(6)-C82 was synthesized and characterized. Inspired by this investigation, four non-IPR YCN@C1(17459)-C76, YCN@C2v(19138)-C76, YCN@C2(17646)-C76, and YCN@C1(17894)-C76 (1, 2, 3, and 4) containing a pair of adjacent pentagons are designed to explore the encapsulated molecular effect on their interaction energies and nonlinear optical properties. The interaction energy (E int) values of 1, 2, 3, and 4 are -481.35 (1), -477.91 (2), -482.04 (3), -482.69 (4) kcal mol(-1), respectively, which shows that the E int value of 4 is the largest. Furthermore, the electron-transfer is mainly from the YCN to C76 cage. When YCN is encapsulated into C76 cage, we can find that the α0 values of the four molecules are very close, ranging from 6.50 × 10(2) to 6.65 × 10(2) au. Significantly, the first hyperpolarizabilities are in relation to the encapsulated molecular: 1.63 × 10(3) (1) > 8.03 × 10(2) (2) > 7.76 × 10(2) (4) > 4.86 × 10(2) au (3), the results show that the βtot value of 1 is the largest. Besides this, the encapsulation of the YCN to C76 cage brings some distinctive changes in its UV-vis spectra along with its other electronic properties that might be used by the experimentalists to develop the potential nonlinear optical nanomaterials based on endohedral metallofullerenes.

Theoretical Insight into the Ambiguous Endohedral Metallofullerene Er3C74: Covalent Interactions among Three Lanthanide Atoms

All of C74-based endohedral metallofullerenes (EMFs) are found to be monometallofullerenes with the same D3h(14246)-C74 cage so far. An opening question is whether other C74 cages could survive during the production of some novel C74-EMFs. Theoretically, we studied the trimetallic endohedral fullerene Er3C74, the existence of which had been proven without any further characterizations. Two thermodynamically stable Er3C74 isomers were obtained, both of which could be expressed as Er3@C74, meaning that previously synthesized Er3C74 is indeed an endohedral trierbium fullerene. Besides the isomer with well-known D3h(14246)-C74 cage which obeys isolated pentagon rule (IPR), another one possesses the C1(13771)-C74 cage with two adjacent pentagons. Notably, it is the first time an endohedral metallofullerene containing the C1(13771)-C74 cage has been reported. Frontier orbitals analysis, bonding analysis in terms of quantum theory of atoms-in-molecule (QTAIM) and Mayer bond order, together with two-dimensional maps of electron localization function (ELF) and Laplacian of electron density of Er3@D3h(14246)-C74 and Er3@C1(13771)-C74 show obvious covalent interactions not only between metallic atoms and carbon cage but also among three erbium atoms. Finally, simulated IR spectra of Er3@D3h(14246)-C74 and Er3@C1(13771)-C74 were simulated, which should be useful to distinguish those two isomers.

Regioselective chlorine-addition reaction toward C54Cl8 and role of chlorine atoms in Stone-Wales rearrangement

By means of density functional theory, detailed studies of regioselective chlorine-addition reactions of two C(54)Cl(8) isomers disclose a highly competitive advantage of (#540)C(54)Cl(8) in the chlorofullerene formation process. The regioselectivity of the addition pattern in (#540)C(54)Cl(8) is found to be dependent on both local and general factors. Special structural relationships reveal that the pristine cage of (#540)C(54)Cl(8) can transform to that of (#864)C(56)Cl(10) and (#913)C(56)Cl(12) through both C(2) addition and Stone-Wales rearrangement. It is found that Stone-Wales rearrangement, which is believed to be a high energy barrier reaction, can be facilitated remarkably well if chlorine atoms participate in the rearrangement process. Furthermore, investigation into the electronic properties of C(54) exohedral fullerenes reveal the different impacts of halogen and hydrogen atoms.

C₇₄ endohedral metallofullerenes violating the isolated pentagon rule: a density functional theory study

Precise studies on M(2)@C(74) (M = Sc, La) series by means of DFT methods have disclosed that certain non-IPR isomers are more stable than the IPR structure. M(2)@C(2)(13295)-C(74) and M(2)@C(2)(13333)-C(74), both of which have two pentagon adjacencies (PA), present excellent thermodynamic stability with very small energy differences. Statistical mechanics calculations on the M(2)@C(74) series reveal that M(2)@C(2)(13295)-C(74) and M(2)@C(2)(13333)-C(74) are quite favoured by entropy effects below 3000 K. Sc(2)@C(74) and La(2)@C(74) series are found to have similar electronic transfer but different electronic structures due to the distinct properties of scandium and lanthanum elements according to Natural Bond Orbital (NBO) analysis in conjunction with orbital interaction diagrams. Investigations of bonding energies reflect quite different influences of the two types of metal atoms to C(74) metallo-fullerenes. Further examinations on C(74) metallo-fullerenes uncover significant stabilization effects of metal atoms acting on PA fragments. Geometrical structures of certain non-IPR cages (from C(72) to C(76)), which exhibit splendid stabilities when encapsulating metallo-clusters, are found to be related by Stone-Wales transformation and C(2) addition. Furthermore, IR spectra and (13)C NMR spectra of M(2)@C(2)(13295)-C(74) and M(2)@C(2)(13333)-C(74) have been simulated to assist further experimental characterization.