Abstract ：

In comparison with the prevalent 2D material-supported single atom catalysts (SACs), the design and fabrication of SACs with single molecule substrates are still challenging. Here we introduce a new type of SAC in which a recently identified all-boron fullerene B40is employed as the support and its catalytic performance toward the nitrogen reduction reaction (NRR) process is explored in theory. Taking advantage of the novel heptagonal ring substructure on the sphere and the electron-deficient nature of boron, the atomic metals are facile to reside on B40to form atomically dispersed η7-B40M exohedral complexes. Among a series of candidates, originating from the proper metal-adsorbate interactions, the atomic tungsten-decorated B40W is screened out as the most feasible catalyst for the NRR with a low over-potential and high selectivity to passivate the competitive hydrogen evolution process. © the Owner Societies 2021.

Keyword ：

Atoms Boron Catalyst selectivity Nitrogen Substrates Tungsten

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Abstract ：

Y2C2@C(82)series (as well as Y-2@C(84)series) and the parent C(82)cages were investigated by density functional theory in conjunction with statistical thermodynamic analyses. C-2(39717)-C(82)is the most stable isomer of pristine C(82)cages, and Y-2@D-2d(51591)-C(84)is the most low-lying isomer of Y(2)C(84)series. At the temperature range of fullerene formation, C-2(39712)-C-82, C-s(39713)-C-82, and C-3v(39717)-C(82)are the three most abundant C(82)isomers, and Y2C2@C-s(39715)-C-82, Y2C2@C-3v(39717)-C-82, and Y2C2@C-2v(39718)-C(82)are the three only abundant Y(2)C(84)isomers. However, mole fraction of Y-2@D-2d(51591)-C(84)turns to be very low at the high temperature range. Further statistical thermodynamic analyses revealed that vibrational frequencies are the underlying reason for high abundances of Y2C2@C-s(39715)-C-82, Y2C2@C-3v(39717)-C-82, and Y2C2@C-2v(39718)-C(82)and low abundance of Y-2@D-2d(51591)-C(82)at high temperature range. The statistical thermodynamic analysis approach to separately consider energy, rotation and vibration partition functions can be used to investigate other endohedral metallofullerenes.

Keyword ：

Computational Chemistry Density Functional Theory Endohedral Metallofullerene Fullerenes Thermodynamic Stability

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Abstract ：

Four-electron transfer from U to the fullerene cage commonly exists in U@C-2n, (2n < 82) so far, while four- and three-electron transfers, which depend on the cage isomers, simultaneously occur in U@C-82. Herein, detailed quantum-chemicaI methods combined with statistical thermodynamic analysis were applied to deeply probe into U@C-84, which is detected in the mass spectra without any further exploration. With triplet ground states, novel isomers including isolated-pentagon-rule U@C-2(51579)-C-84 and U@D-2(51573) -C-84 as well as nonisolated-pentagon-rule U@C-5(51365)-C-84 were identified as thermodynamically optimal. Surprisingly, there were unexpected three-electron transfers, which directly led to one unpaired electron on the cage, in all of the three isomers. Significant covalent interactions between the cage and U successively weakened for U@D-2(51573)-C-84, U@C-2(51579)-C-84, and U@C-5(51365)-C-84. Besides, the IR absorption spectra were simulated as a reference for further structural identification in the experiment. Last but not least, the potential reaction sites were predicted to facilitate further functionalization and thus achieve promising applications for U@C-84.

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Abstract ：

The title reaction is theoretically investigated in detail using density functional theory. Three possible routes starting from keto-or enol-type vinylcyclopropylketone are considered in this work. Results indicate that phosphine catalyst would first attack at the three-membered ring (C3 position) rather than the terminal of alkene (C1 position) in vinylcyclopropylketone. It is found that the two-stage mechanism would be responsible for the title reaction. The first stage is the S(N)2'-type ring-opening of the keto-type vinylcyclopropylketone with phosphine catalyst. After the proton-transfer tautomerisms in the zwitterionic intermediates, the second stage is associated with the 7-endo-trig S(N)2'-type ring closure of keto- or enol-type zwitterions to furnish seven-membered cyclic products and recover the catalyst. Moreover, it turns out that 7-endo-trig S(N)2'-type ring closure would be highly asynchronous and could be well described as an addition/elimination process where the ring closure already finishes before the cleavage of the C-P bond. Computational results provide a deep insight into experimental observations.

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Nonclassical fullerene is a new member of the fullerene family. In the present work, a systematic investigation on LaxSc3-xN@C-80 (x = 0-3) covering both classical and nonclassical C80 cages was performed utilizing density functional theory combined with statistical mechanics. At absolute zero, LaSc2N@Hept(6)-C-s(2)-C-80 with a heptagon-containing nonclassical carbon is the second most stable isomer, whereas at the temperature range of endohedral metallofullerene (EMF) formation, due to the large vibrational frequencies, LaSc2N@Hept(6)-C-s(2)-C-80 is the third most abundant isomer, and its mole fraction is very low, accounting for the low experimental yield of LaSc2N@Hept(6)-C-s(2)-C-80; La2ScN@Hept(6)-C-s(2)-C-80, and La3N@Hept(6)-C-s(2)-C-80 are the overwhelming isomers of the corresponding series, but compared with the cases of Sc3N@C-80 and LaSc2N@C-80, La2ScN and La3N clusters suffer much larger constraints from the C-80 cages, perhaps preventing the synthesis of La2ScN@C-80 and La3N@C-80 species. Because of the large mole fractions and large electron donation and back-donation of La2ScN@Hept(6)-C(2)-C-80 and La3N@Hept(6)-C-s(2)-C-80, it can be inferred that La2ScN and La3N clusters may be used to stabilize some other larger nonclassical fullerene cages. This work will provide useful insights into the origins of stabilization of nonclassical fullerene cages by endohedral derivation and guidelines for synthesis EMF with nonclassical cages.

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A MSc2N@C-70 (M = Sc, Y, Dy) family has been systematically investigated by density functional calculations in conjunction with statistical thermodynamic analyses for the first time. The results revealed that C-2 nu(7854)-C-70 is the most predominant carbon cage when encapsulating DySc2N, YSc2N, and Sc3N clusters. In addition, endohedral structures based on C-1(7852)-C-70 and C-1(7851)-C-70 are also stable with large concentrations in the temperature region of fullerene formation. All these three isomers are non-IPR structures with three pentagon adjacencies (PA) and related by Stole-Wales transformation. The interaction energies (INT) of MSc2N@C-2 nu(7854)-C-70, MSc2N@C-1 (7852)-C-70, and MSc2N@C-1(7851)-C-70 are much more negative than those of the IPR structures MSc2N@D-sh(8149)-C-70, revealing a stabilizing effect of the MSc2N (M = Sc, Y, Dy) clusters toward the PAs. On the basis of the ionic model of (MSc2N)(6+)@C-70(6-), which is confirmed by the frontier orbital analyses, the electron back-donation from C-70(6-) to (MSc2N)(6+) increases in the order of Sc3N@C-70 < YSc2N@C-70 < DySc2N@C-70. Therefore, the INT value increases in the order of Sc3N@C-70 < YSc2N@C-70 < DySc2N@C-70, suggesting that the stabilizing effect of the endohedral cluster is weakened by Y and Dy. Moreover, the UV-vis-NIR spectra of MSc2N@C-2 (7854)-C-70 (M = Sc, Y, Dy) coincide with the experimental characterizations well, and simulations for other isomers will be helpful for further identification of those metal nitride clusterfullerenes.

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The successful synthesis and isolation of cyclo-C-18 in experiments is a ground-breaking development in carbon rings. Herein, we studied the thermodynamic stabilities of cyclo-C-n (4 <= n <= 34) with hybrid density functional theory. When n = 4N + 2 (N is an integer), cyclo-C-n were thermodynamically stable. In particular, cyclo-C-10 and cyclo-C-14 were more thermodynamically, kinetically, dynamically, and optically stable compared with the acknowledged cyclo-C-18, and were potential candidates for zero-dimensional carbon rings. Cyclo-C-n (n = 10 and 14) show similar molecular semiconductor characteristics to the acknowledged cyclo-C-18. The carbon atoms were sp hybridized in cyclo-C-10, cyclo-C-14, and cyclo-C-18. Cyclo-C-14 and cyclo-C-18 had alternating abnormal single and triple bonds, but cyclo-C-10 had equal bonds. Cyclo-C-10, cyclo-C-14, and cyclo-C-18 with large aromaticities had out-of-plane and in-plane pi systems, which were perpendicular to each other. The number of pi electrons in the out-of-plane and in-plane pi systems, respectively, followed the standard Huckel aromaticity rule. Simulated UV-vis-NIR spectra indicated similar electronic structures of cyclo-C-14 and cyclo-C-18.

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The detailed mechanism and origins of gold-catalyzed domino cyclization to indoloazocines by density functional theory are systematically studied. The energy profiles for [Au(PMe3)](+)and [Au(PMe3)SbF6] were investigated. Specifically, the gold-counterion dual catalysis mechanism was the most plausible mechanism for domino cyclization to spiroindolines because of its periplanar cooperation, small activation energy, and hydrogen bonding interactions in the transition states (TS) and intermediates. Based on the Curtin-Hammett principle, the calculated activation energy of 21.0 kcal mol(-1)was the rate-determining step for the overall reaction. Besides, the energy profiles for three different models,i.e.catalysts with OTf(-)counterion, BF(4)(-)counterion, and THF solvent, were investigated to confirm the role of hydrogen bonding interactions in the cooperative dual catalysis mechanism. Thus, the obtained theoretical results not only well rationalize the experimental results but also provide insights into the details of the domino cyclization.

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Abstract ：

Fullerenes are important zero-dimensional materials in photoelectric, antioxidant, pharmaceutical, and single-molecular-magnet fields, but the fullerene- formation mechanism has been elusive since the discovery of C-#1812(60)_ I-h in 1985 because of the missing key links and low yield. Therefore, experimental and theoretical research is required to explore some fundamental questions of the fullerene-formation mechanism. Considering the temperature, here we carried out two fullerene-formation models, bottom-up and top-down, for C-2n (50 <= 2n <= 70) containing optical enantiomers, heptagons, and tetragons via density functional and transition-state theories. The thermodynamically and kinetically preferred pathway for C-2n (so <= 2n <= 70) was the bottom-up model instead of the top-down model. Furthermore, this is the first time revealing that the enantiomer and enthalpy play key roles in forming fullerenes C-2n (50 <= 2n <<= 70). Especially, the effect of the enantiomer on the fullerene-formation mechanism had been neglected in previous research.

Keyword ：

competitive relationship between the top-down and bottom-up models density functional theory enantiomer and enthalpy key roles in the top-down model thermodynamic and kinetic fullerene formationmechanisms

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Thermodynamically stable La@C-2v(24 107)-C-78, La@D-3h(24 109)-C-78, La@C-1(22 595)-C-78, Ce@D-3h(24 109)-C-78, Sm@C-2v(24 107)-C-78, and Sm@D-3h(24 109)-C(78)based on density functional theory and statistical thermodynamic analysis are studied in theory.C-1(22 595)-C-78, violating the isolated pentagon rule, is a second novel isomer stabilized by encaging a La atom. In addition, three- and two-electron transfers occur in M@C-78(M = La and Ce) and Sm@C-78, respectively. Although there are two electrons transferred from Sm to C-78, these electrons transferred to the surface ofC(2v)(24 107)-C(78)are unpaired. Thus, the surface of the endohedral metallofullerene, Sm@C-2v(24 107)-C-78, firstly displays diradical characteristics. Notably, the spin states of the two electrons transferred from Sm toD(3h)(24 109)-C(78)are different from those onC(2v)(24 107)-C-78, leading to different spin ground states. Furthermore, the natural bond orders and bond critical point analyses on thermodynamically stable M@C-78(M = La, Ce, and Sm) reveal that the distance between the metal and carbon atom plays an important role in the covalent interaction between the inner metal atoms and C-78. Because of the strong ionic interaction, the studies on the magnetic character of M@C-78(M = La, Ce, and Sm) show that Sm@C(78)is a promising candidate for single-molecule magnets with high isotropic susceptibility. The infrared spectra were simulated to facilitate further experimental study on the stable M@C-78(M = La, Ce, and Sm). We believe that this work will provide good guidance and assistance for the further study of mono-metallofullerenes and coordination compounds in both experiment and theory.

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