Search Results (8)

Calculations are presented for the encapsulation of two CO₂ molecules in the most common C₈₄ fullerenes, producing (CO₂)₂@$D_2$(22)-C₈₄ and (CO₂)₂@$D_{2d}$(23)-C₈₄. The calculations are performed at the DFT M06-2X/6-31+G* level with the BSSE correction. The encapsulation energy for (CO₂)₂@$D_2$(22)-C₈₄ and (CO₂)₂@$D_{2d}$(23)-C₈₄ is calculated as −4.9 and −5.6 kcal/mol, respectively. The encapsulation of two CO₂ molecules is attractive, though the energy gain is, owing to a steric hindrance, smaller than previously found for the encapsulation of one CO₂. The IR vibrational spectra are presented, too. Full article

This article presents computational studies of non-metal fullerene endohedrals, which are useful for understanding and interpreting experimental results. The encapsulated non-metal species are simple molecules like H₂, N₂, CO, HF, NH₃, H₂O₂, H₂O, and their aggregates. Predictions of thermodynamic stability and reaction populations are reviewed, based on quantum-chemical and statistical–thermodynamic treatments. As fullerene syntheses are performed at high temperatures, some of the calculations are based on both the encapsulation potential energy and the encapsulation Gibbs energy changes. Full article

Encapsulations of carbon dioxide into $D_2$(22)-${\mathrm{C}}_{84}$ and $D_{2d}$(23)-$C_{84}$ fullerenes are evaluated. The encapsulation energy is computed with the DFT M06-2X/6-31+${\mathrm{G}}^{*}$ approach corrected for the basis set superposition error evaluated by the counterpoise method. The resulting encapsulation energy for ${\mathrm{CO}}_2$@$D_2$(22)-${\mathrm{C}}_{84}$ and ${\mathrm{CO}}_2$@$D_{2d}$(23)-${\mathrm{C}}_{84}$ amounts to substantial values of −14.5 and −13.9 kcal/mol, respectively. The energy gain is slightly larger than for CO@${\mathrm{C}}_{60}$, already synthesized with a high-temperature and high-pressure treatment—so that a similar preparation of ${\mathrm{CO}}_2{@\mathrm{C}}_{84}$ could be possible. The calculated rotational constants and IR vibrational spectra are presented for possible use in detection. The stability of ${\left({\mathrm{CO}}_2\right)}_2$${@\mathrm{C}}_{84}$ is also briefly discussed. Full article

The recently synthetically prepared endohedral CH₄@C₆₀ was characterized here using calculations—namely its structure, energetics, thermodynamics, and vibrational spectrum. The calculations were carried out with DFT (density-functional theory) methods, namely by the DFT M06-2X functional and MP2, as well as B2PLYPD advanced correlated, treatments with the standard 6-31++G** and 6-311++G** basis sets, corrected for the basis set superposition error evaluated using the approximative Boys–Bernardi counterpoise method. The symmetry of the endohedral obtained in the geometry optimizations was tetrahedral T. The energetics of CH₄ encapsulation into C₆₀ was attractive (i.e., with a negative encapsulation-energy term), producing a substantial energy gain of −13.94 kcal/mol at the most advanced computational level, B2PLYPD/6-311++G**. The encapsulation equilibrium constants for CH₄@C₆₀ were somewhat higher than previously found with the CO@C₆₀ system. For example at 500 K, the encapsulation equilibrium constant for CH₄@C₆₀ had a value one order of magnitude larger than for CO@C₆₀. The encapsulation thermodynamic characteristics suggest that high-pressure and high-temperature synthesis could in principle also be possible for CH₄@C₆₀. Full article

Metal cyanide clusterfullerenes (CYCFs) are formed via the encapsulation of a single metal atom and a cyanide unit inside fullerene cages, endowing them with excellent properties in various applications. In this work, we report the synthesis, isolation, and characterizations of the first cases of thulium (Tm)-based CYCFs with the popular C₈₂ carbon cages. The structural elucidation of the two TmCN@C₈₂ isomers was achieved via diverse analytical techniques, including mass spectrometry, Vis-NIR spectroscopy, single-crystal X-ray crystallography, and cyclic voltammetry. The crystallographic analyses unambiguously confirmed the molecular structures of the two TmCN@C₈₂ isomers as TmCN@C_s(6)-C₈₂ and TmCN@C_2v(9)-C₈₂. Both TmCN clusters adopt a well-established triangular configuration, with the Tm ion located on the symmetrical plane of the carbon cages. The electronic structures of both TmCN@C₈₂ isomers adopt a Tm³⁺(CN)⁻@(C₈₂)²⁻ configuration, exhibiting characteristic spectral and electrochemical properties reminiscent of divalent endohedral metallofullerenes (EMFs). Intriguingly, unlike the divalent Tm²⁺ ion observed in the mono-metallofullerenes Tm@C_2n, a higher oxidation state of Tm³⁺ is identified in the monometallic TmCN cluster due to bonding with the cyanide anion. This result provides valuable insight into the essential role of the non-metallic endo-units in governing the oxidation state of the metal ion and the electronic behaviors of EMFs. Full article

Electronic and nonlinear optical properties of endohedral metallofullerenes are presented. The endohedral metallofullerenes contain transition metal encapsulated in inorganic fullerenes X₁₂Y₁₂ (X = B, Al & Y = N, P). The endohedral metallofullerenes (endo-TM@X₁₂Y₁₂) possess quite interesting geometric and electronic properties, which are the function of the nature of the atom and the size of fullerene. NBO charge and frontier molecular orbital analyses reveal that the transition metal encapsulated Al₁₂N₁₂ fullerenes (endo-TM@Al₁₂N₁₂) are true metalides when the transition metals are Ni, Cu and Zn. Endo-Cr@Al₁₂N₁₂ and endo-Co@Al₁₂N₁₂ are at the borderline between metalides and electrides with predominantly electride characteristics. The other members of the series are excess electron systems, which offer interesting electronic and nonlinear optical properties. The diversity of nature possessed by endo-TM@Al₁₂N₁₂ is not prevalent for other fullerenes. Endo-TM@Al₁₂P₁₂ are true metalides when the transition metals are (Cr-Zn). HOMO-LUMO gaps (E_H-L) are reduced significantly for these endohedral metallofullerenes, with a maximum percent decrease in E_H-L of up to 70%. Many complexes show odd–even oscillating behavior for E_H-L and dipole moments. Odd electron species contain large dipole moments and small E_H-L, whereas even electron systems have the opposite behavior. Despite the decrease in E_H-L, these systems show high kinetic and thermodynamic stabilities. The encapsulation of transition metals is a highly exergonic process. These endo-TM@X₁₂Y₁₂ possess remarkable nonlinear optical response in which the first hyperpolarizability reaches up to 2.79 × 10⁵ au for endo-V@Al₁₂N₁₂. This study helps in the comparative analysis of the potential nonlinear optical responses of electrides, metalides and other excess electron systems. In general, the potential nonlinear optical response of electrides is higher than metalides but lower than those of simple excess electron compounds. The higher non-linear optical response and interesting electronic characteristics of endo-TM@Al₁₂N₁₂ complexes may be promising contenders for potential NLO applications. Full article

This report deals with the quantum-chemical evaluation of the energetics and thermodynamics of the simultaneous encapsulation of HF and H${}_2$O by the IPR (isolated pentagon rule) C${}_{70}$ fullerene cage, yielding ${\mathrm{H}}_2\mathrm{O}·\mathrm{HF}@{\mathrm{C}}_{70}$ species which were synthesized and characterized recently, thus further expanding the family of fullerene endohedrals with non-metallic encapsulates. The structures were optimized at the DFT (density functional theory) M06-2X/6-31++G** level. The encapsulation energetics were further refined by the advanced B2PLYPD/6-31++G** and B2PLYPD/6-311++G** methods. After enhancement of the B2PLYPD/6-311++G** encapsulation energy for the BSSE and steric corrections, the encapsulation energy gain was obtained, as 26 kcal/mol. The equilibrium encapsulation thermodynamics were described using the M06-2X/6-31++G** partition functions. The results correspond to our previous evaluations for the water dimer encapsulation by C${}_{84}$ cages. Full article

Endohedral metal fullerene are potential nanopharmaceuticals for MRI; thus, it is important to study their effect on reactive oxygen species (ROS) homeostasis. Superoxide anion radical is one of the key ROS. The reactivity of aqueous dispersions of pristine (non-functionalized) fullerenes and Gd@C₈₂ endofullerene have been studied with respect to superoxide in the xanthine/xanthine oxidase chemiluminescence system. It was found that C₆₀ and C₇₀ in aqueous dispersions react with superoxide as scavengers by a similar mechanism; differences in activity are determined by cluster parameters, primarily the concentration of available, acting molecules at the surface. Gd endofullerene is characterized by a significantly (one-and-a-half to two orders of magnitude) higher reactivity with respect to C₆₀ and C₇₀ and is likely to exhibit nanozyme (SOD-mimic) properties, which can be accounted for by the nonuniform distribution of electron density of the fullerene cage due to the presence of the endohedral atom; however, in the cell model, Gd@C₈₂ showed the lowest activity compared to C₆₀ and C₇₀, which can be accounted for by its higher affinity for the lipid phase. Full article