Palladium-Catalyzed Reaction of [60]Fullerene with Aroyl Compounds via Enolate-Mediated sp2 C-H Bond Activation and Hydroxylation.

A convenient and highly efficient palladium-catalyzed reaction of [60]fullerene (C60) with aroyl compounds via enolate-mediated C-H activation and hydroxylation has been exploited for the first time to synthesize novel C60-fused dihydrofurans, and rare 1,4-fullerenols. Further functionalization including etherification, and esterification of synthesized 1,4-fullerenols provided efficient access to versatile fullerene derivatives. Moreover, a plausible reaction mechanism leading to the observed products is proposed.

Large-area snow-like MoSe2 monolayers: synthesis, growth mechanism, and efficient electrocatalyst application.

This study explores the large-area synthesis of controllable morphology, uniform, and high-quality monolayer. MoSe2 is essential for its potential application in optoelectronics, photocatalysis, and renewable energy sources. In this study, we successfully synthesized snow-like MoSe2 monolayers using a simple chemical vapor deposition method. Results reveal that snow-like MoSe2 is a single crystal with a hexagonal structure, a thickness of ∼0.9 nm, and a lateral dimension of up to 20 µm. The peak position of the photoluminescence spectra is ∼1.52 eV corresponding to MoSe2 monolayer. The growth mechanism of the snow-like MoSe2 monolayer was investigated and comprised a four-step process during growth. Finally, we demonstrate that the snow-like MoSe2 monolayers are ideal electrocatalysts for hydrogen evolution reactions (HERs), reflected by a low Tafel slope of ∼68 mV/decade. Compared with the triangular-shaped MoSe2 monolayer, the hexangular snow-like shape with plentiful edges is superior for perfect electrocatalysts for HERs or transmission devices of optoelectronic signals.

Synthesis of New Bis(3-hydroxy-4-pyridinone) Ligands as Chelating Agents for Uranyl Complexation.

Five new bis(3-hydroxy-4-pyridinone) tetradentate chelators were synthesized in this study. The structures of these tetradentate chelators were characterized by ¹H-NMR, (13)C-NMR, FT-IR, UV-vis, and mass spectral analyses. The binding abilities of these tetradentate chelators for uranyl ion at pH 7.4 were also determined by UV spectrophotometry in aqueous media. Results showed that the efficiencies of these chelating agents are dependent on the linker length. Ligand 4b is the best chelator and suitable for further studies.

An isomer of C60Cl10 free of skew-pentagonal-pyramidal C60Cl6 substructure.

Chlorination is an effective approach for understanding the feature of multiple additions on fullerene cages. The chlorofullerenes obtained are versatile synthons for further derivatization. However, chlorofullerenes used for chemical reaction studies are mainly based on the skew-pentagonal-pyramidal (SPP) C60Cl6. In this work, a new isomer of C60Cl10 that does not contain an SPP-C60Cl6 substructure was identified. Its electrochemical properties give it unexpected cyclic voltammetric behavior at more negative potentials relative to other chlorofullerenes. Friedel-Crafts arylation shows good reactivity of this compound. These new findings challenge opinions of fullerene addition patterns and will break the monopoly of C60Cl6 as a precursor for fullerene modifications.

Study on the thermal reactions of [60]fullerene with amino acids and amino acid esters.

Thermal reactions of [60]fullerene with a series of amino acids and amino acid esters under aerobic and dark conditions have been investigated. Fulleropyrrolidines can be obtained from these reactions although an aldehyde is not added purposely. Possible reaction mechanisms involving uncommon C-N bond cleavages have been proposed to generate aldehydes, which then react with amino acids and amino acid esters to provide azomethine ylides, followed by 1,3-dipolar cycloaddition to [60]fullerene affording fulleropyrrolidines. Control experiments support our proposed mechanisms, and elucidate the innate nature of C-N bond cleavages of amino acids and amino acid esters.

On the shock sensitivity of explosive compounds with small-scale gap test.

In this work an improved set of small-scale gap tests was applied to measure the shock sensitivity of 13 explosive compounds, and a Mn-Cu manometer was also employed to measure the output pressures of shock waves passed through aluminum gaps with different thicknesses to draw a standard curve. The critical initiation thicknesses of aluminum gaps of different explosive compounds (244 shots in total) were treated according to statistical method, and the Mulliken charges of nitro groups, bond dissociation energies of X-NO(2) (X = C, N), resonance energies, and ring strain energies of these explosive compounds were calculated with the means of DFT/BLYP/DNP calculations and homodesmotic reactions designs. Genetic function approximation was used to construct a relationship between the critical initiation thicknesses of aluminum gaps of different explosive compounds and their forementioned molecule structural parameters.

Theoretical investigation of an energetic fullerene derivative.

A self-consistent estimation method for the thermochemical properties of N-methyl-3-(2',4',6'-trinitrobenzene)-fulleropyrrolidine (MTNBFP) is presented. This method is based on enthalpy of formation (Delta(f)H(m)(minus sign in circle)) and enthalpy of combustion obtained from BLYP/DNP calculations of the total energies and frequencies for MTNBFP. The enthalpy of formation was calculated by an optimized set of isodesmic reactions given the available experimental Delta(f)H(m)(minus sign in circle) of relative compounds. MTNBFP has a high enthalpy of formation, 2782.2 kJ/mol. Detonation velocity and detonation pressure were also presented in terms of Kamlet and Jacobs equations. Drop hammer impact sensitivity tests and blasting point per 5 s tests indicate MTNBFP may be a potential candidate primary explosive. To understand the test results well, we proposed a series of chemical reaction mechanisms and interpreted the relationship between impact sensitivity and electronic structures from the viewpoint of nitro group charge, electrostatic potential, and vibrational modes.

Novel insensitive energetic-cocrystal-based BTO with good comprehensive properties.

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared a structurally unusual 1H,1'H-5,5'-bistetrazole-1,1'-diolate (BTO) based energetic cocrystal, which we also confirmed by single-crystal X-ray diffraction and powder-crystal X-ray diffraction. The obtained cocrystal crystallizes in a triclinic system, P-1 space group, with a density of 1.72 g cm-3. The properties including the thermal stability, sensitivity and detonation performance of the cocrystal were analyzed in detail. In addition, the thermal decomposition behavior of the cocrystal was studied by differential calorimetry and thermogravimetry tandem infrared spectroscopy. The results indicated that the cocrystal exhibits strong resistance to thermal decomposition up to 535.6 K. The cocrystal also demonstrates a sensitivity of >50 J. Moreover, its formation enthalpy was estimated to be 2312.0 kJ mol-1, whereas its detonation velocity and detonation pressure were predicted to be 8.213 km s-1 and 29.1 GPa, respectively, by applying K-J equations. Therefore, as expected, the obtained cocrystal shows a good comprehensive performance, which proves that a high degree of layer-by-layer stacking is essential for the structural density, thermal stability and sensitivity.

Synthesis, Characterization, Thermal Stability and Sensitivity Properties of New Energetic Polymers-PVTNP-g-GAPs Crosslinked Polymers.

A series of energetic polymers, poly(vinyl 2,4,6-trinitrophenylacetal)-g-polyglycidylazides (PVTNP-g-GAPs), were synthesized via cross-linking reactions of PVTNP with three different molecular weight GAPs using toluene diisocyanate as the cross-linking agent. The structures of these energetic polymers were characterized by ultraviolet visible spectra (UV⁻Vis), attenuated total reflectance-Fourier transform-infrared spectroscopy (ATR-FTIR), and nuclear magnetic resonance spectrometry (NMR). The glass-transition temperatures of these energetic polymers were measured with differential scanning calorimetry (DSC) method, and the results showed that all the measured energetic polymers have two distinct glass-transition temperatures. The thermal decomposition behaviors of these energetic polymers were evaluated by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and thermogravimetric analysis tandem infrared spectrum (TGA-IR). The results indicated that all the measured energetic polymers have excellent resistance to thermal decomposition up to 200 °C, and the initial thermal decomposition was attributed to the breakdown of azide group. Moreover, the sensitivity properties of these energetic polymers were measured with the national military standard methods and their compatibilities with the main energetic components of 2,4,6-trinitrotoluene (TNT)-based melt-cast explosive were evaluated by using the DTA method. The results indicate that these energetic polymers have feasible mechanical sensitivities and can be safely used with TNT, cyclotetramethylene tetranitramine (HMX), 1,1-diamino-2,2-dinitroethene (FOX-7), 3-nitro-1,2,4-triazol-5-one (NTO) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).

Ab initio molecular dynamics simulation on the formation process of He@C60 synthesized by explosion.

The applications of endohedral non-metallic fullerenes are limited by their low production rate. Recently, an explosive method developed in our group shows promise to prepare He@C60 at fairly high yield, but the mechanism of He inserting into C60 cage at explosive conditions was not clear. Here, ab initio molecular dynamics analysis has been used to simulate the collision between C60 molecules at high-temperature and high-pressure induced by explosion. The results show that defects formed on the fullerene cage by collidsion can effectively decrease the reaction barrier for the insertion of He into C60, and the self-healing capability of the defects was also observed.

An important factor in relation to shock-induced chemistry: resonance energy.

With density function theory BLYP/DNP method, together with homodesmotic reactions and isodesmic reactions, we calculated the resonance energies of some explosives, including eight nitro compounds which contains benzene rings, three nitro compounds which contains azaheterocycles (2,4-dinitroimidazole (2,4-DNI), 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) and 2,4,6-trinitro-1,3,5-triazine) and one nitrogen-rich energetic compound of 3,3'-azobis(6-amino-s-tetrazine) (DAAT). The results indicate that their resonance energies are in relation to their shock sensitivity which measuring their threshold pressures of initiation, that is, the lower the resonance energy is, the higher the shock sensitivity of the explosive behaves. And this measuring method according to resonance energy is based on the global property of the molecule instead of the local one, such as one nitro group in the molecule. It is meaningful to calculate resonance energies of these kind of compounds quickly and accurately because resonance structures exist widely in these organic compounds and resonance energies may play a significant role in determining their shock sensitivity, and it is helpful in the rational design or synthesis of high energy and insensitive materials.

The studies on the aromaticity of fullerenes and their holmium endohedral compounds.

Density functional theory BLYP/DNP was employed to optimize a series of fullerenes and their holmium endohedral compounds, including C(20), Ho@C(20), Ho(3+)@C(20), C(60), Ho@C(60), Ho(3+)@C(60),C(70), Ho@C(70), Ho(3+)@C(70) C(78), Ho@C(78), Ho(3+)@C(78), C(82),Ho@C(82) and Ho(3+)@C(82). DFT semi core pseudospot approximation was taken into consideration in the calculations of the element holmium because of its particular electronic structure. Fullerenes and their holmium endohedral compounds' aromaticity were studied in terms of structural criteria, energetic criteria, and reactivity criteria. The results indicate that the aromaticity of fullerenes was reduced when a holmium atom was introduced into the carbon cage, and the endohedral fullerenes' reactive activity enhance; but the aromaticity of the carbon cage increased when a Ho(3+) cation was encapsulated into a fullerene. Calculations of aromaticity and stability indicate that two paths can lead to the similar aim of preparing holmium endohedral fullerenes; that is, they can form from either a holmium atom or a holmium cation (Ho(3+)) reacting with fullerenes, respectively, and the latter is more favorable.

Two important factors influencing shock sensitivity of nitro compounds: Bond dissociation energy of X-NO2 (X = C, N, O) and Mulliken charges of nitro group.

DFT/BLYP/DNP is employed to calculate bond dissociation energy of X-NO(2) (X = C, N, O) and Mulliken charges of nitro group of 14 kinds of nitro compounds, and partial least squares approximation is applied to linearly fit their shock initiation pressure (p(90%,TMD)). It is found that the fitted values are in good agreement with the experimental shock initiation pressures. The fitted model is used to predict the shock initiation pressures of two kinds of explosives, TNB and TNETB. The predictive values are in accordance with experimental ones. It reflects that bond dissociation energy of X-NO(2) (X = C, N, O) and Mulliken charge of nitro groups may be the important factors influencing the shock sensitivity of nitro compounds. On the basis of the fitted model, bond dissociation energy of X-NO(2) (X = C) and Mulliken charges of nitro groups of another 14 kinds of heterocyclic nitro compounds are in consideration to predict shock sensitivity. This work is meaningful in further understanding the shock mechanism and helpful to the design and synthesis of novel energetic materials.