BN-Doped Fullerenes: An NICS Characterization

Effects of orbital angles on the modeling of conjugated systems with curvature

Models with angle corrections give well predictions of both neutral and charged fullerenes. The integrals of nonparallel orbitals explain why angle features of designed and deep-learning models are necessary to describe conjugated systems.

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto-Enol Tautomerization Process of α- and β-Cyclodiones

We have explored the effect of ring size on keto-enol tautomerization of α- and β-cyclodiones using the M062X-SMD_aq/6-31+G(d,p)//M062X/6-31+G(d,p) level of theory. The calculated results show that the activation free energy barrier for the keto-enol tautomerization process of α-cyclopropanedione (1) is 54.9 kcal/mol, which is lower compared to that of the other cyclic diketo systems studied here. The four-membered α- and β-cyclobutanedione (2 and 6) do not favor keto-enol tautomerization unlike other studied cyclic systems because of the ring strain developed in the transition-state geometries and their corresponding products. Water-assisted keto-enol tautomerization with one molecule reveals that the free energy activation barriers reduce almost half compared to those for the uncatalyzed systems. The two-water-assisted process is favorable as the activation free energy barriers lowered by ∼10 kcal/mol compared to those of the one-water-assisted process. The ion-pair formation seems to govern the lowering of activation barriers of α- and β-cyclodiones with two water molecules during the keto-enol tautomerization process, which however also overcomes the favorable aromatization in the three-membered ring system. The free energy activation barriers calculated with the M062X-SMD_aq/6-31+G(d,p) level predicted that the keto-enol tautomerization process for the α-cyclodiones follows the following trend: 2 > 3 > 4 > 5 > 1. Water-assisted tautomerization of α-cyclodiones also predicted 1-W and 1-2W as the most favored processes; however, 5-W and 5-2W were found to be disfavored in this case. The β-cyclodione systems also showed similar trends as obtained with α-diketone systems. The influence of bulk solvent on the keto-enol tautomerization process favors the formation of the enol form in a more polar solvent medium even under mixed solvent conditions in acetonitrile and hexane at M062X-SMD_acetonitrile/6-31+G(d,p) and M062X-SMD_hexane/6-31+G(d,p) levels of theory.

Electrochemical Properties of Boron-Doped Fullerene Derivatives for Lithium-Ion Battery Applications

The high electron affinity of fullerene C₆₀ coupled with the rich chemistry of carbon makes it a promising material for cathode applications in lithium-ion batteries. Since boron has one electron less than carbon, the presence of boron on C₆₀ cages is expected to generate electron deficiency in C₆₀ , and thereby to enhance its electron affinity. By using density functional theory (DFT), we studied the redox potentials and electronic properties of C₆₀ and C₅₉ B. We have found that doping C₆₀ with one boron atom results in a substantial increase in redox potential from 2.462 V to 3.709 V, which was attributed to the formation of an open shell system. We also investigated the redox and electronic properties of C₅₉ B functionalized with various redox-active oxygen containing functional groups (OCFGs). For the combination of functionalization with OCFGs and boron doping, it is found that the enhancement of redox potential is reduced, which is mainly attributed to the open shell structure being changed to a closed-shell one. Nevertheless, the redox potentials are still higher than that of pristine C₆₀ . From the observation that the lowest unoccupied molecular orbital of closed-shell OCFG- functionalized C₅₉ B is correlated well with the redox potential, it was confirmed that the spin state is crucial to be considered to understand the relationship between electronic structure and redox properties.

Endohedral pnicogen and triel bonds in doped C60 fullerenes

Encapsulation of H_nYF_3−n in C₃₀X₁₅Y₁₅ (X = B, Al and Y = N, P and n = 1, 2) and characterization of the endohedral pnicogen and triel bonds.

The role of aromaticity in determining the molecular structure and reactivity of (endohedral metallo)fullerenes

The molecular structure and chemical reactivity of endohedral metallofullerenes can be greatly predicted and rationalized by their local and global aromaticity.

B-N as a C-C substitute in aromatic systems

The substitution of isoelectronic B–N units for C–C units in aromatic hydrocarbons produces novel heterocycles with structural similarities to the all-carbon frameworks, but with fundamentally altered electronic properties and chemistry. Since the pioneering work of Dewar some 50 years ago, the relationship between B–N and C–C and the wealth of parent all-carbon aromatics has captured the imagination of organic, inorganic, materials, and computational chemists alike, particularly in recent years. New applications in biological chemistry, new materials, and novel ligands for transition-metal complexes have emerged from these studies. This review is aimed at surveying activity in the area in the past couple of decades. Its organization is based on ring size and type of the all-carbon or heterocyclic subunit that the B–N analog is derived from. Structural aspects pertaining to the retention of aromaticity are emphasized, along with delineation of significant differences in physical properties of the B–N compound as compared to the C–C parent.Key words: boron-nitrogen heterocycles, aromaticity, organic materials, main-group chemistry.

Time-Dependent Density Functional Theoretical Study of the Absorption Properties of BN-Substituted C60Fullerenes

Time-dependent density functional theoretical calculations using the B3LYP functional and 6-31G* basis set for a series of BN-substituted C60 fullerenes reveal that, unlike C60, these molecules would absorb in the visible region and that the optical and electronic properties of fullerenes can be fine-tuned with proper BN substitution.

Endohedral Chemistry of C60-Based Fullerene Cages

Fullerenes have unique chemistry owing to their cage structure, their richness in pi-electrons, and their large polarizabilities. They can trap atoms and small molecules to generate endohedral complexes as superconductors, drug carriers, molecular reactors, and ferroelectric materials. An important goal is to develop effective methods that can affect the behavior of the atoms and small molecules trapped inside the cage. In this paper, the quantum chemical density functional theory was employed to demonstrate that the stability and position of a guest molecule inside the C60 cage can be changed, and its orientation controlled, by modifying the C60 cage shell. The outside attachment of two hydrogen atoms to two adjacent carbon atoms located between two six-membered rings of the C60 cage affects the orientation of the LiF molecule inside and increases the stability of LiF inside the cage by 45%. In contrast, when 60 hydrogen atoms were attached to the outside surface of the C60 cage, thus transforming all C=C double bonds into single bonds, the stability of the LiF inside was reduced by 34%. If two adjacent carbon atoms were removed from C60, the stability of LiF inside this defect C60 was reduced by 41%.

Structures and magnetic properties of mono-doped fullerenes C59Xn and C59X(6mn)m (X=Bm, N+, P+, As+, Si): isoelectronic analogues of C60 and C60(6m)

Structures of mono-doped fullerenes, C59Xn and C59X(6mn)m (X=Bm, N+, P+, As+, Si), the isoelectronic analogues to C60 and C606m with 60 and 66 pi-electrons, have been investigated at the B3LYP/6-31G* level of density functional theory. On the basis of the computed nucleus independent chemical shifts (NICS) at the cage center and also at the center of individual rings as magnetic criteria, heterofullerenes with 60 pi-electrons are as aromatic as the parent C60, while those with 66 pi-electrons are much less aromatic than C606m. The very distinct endohedral chemical shifts of the 66 pi-electron systems may be useful to identify the heterofullerenes through their endohedral 3He NMR chemical shifts.