Exohedral functionalization of C60 by [4+2] cycloaddition of multiple anthracenes

By using density functional theory, we have investigated [4+2] cycloaddition of one to four anthracene (ANT) molecules to a C₆₀ fullerene which has been already studied by experimentalists. It was found that the reaction is regioselective and the ANT molecule prefers to be adsorbed atop a C–C bond of the C₆₀ which is shared between two hexagons with reaction energy of ?25.2 kcal/mol (for one ANT). The HOMO of the ANT interacts with the LUMO of the C₆₀ via a cycloaddition reaction. Also five regioisomeric bis-adducts of ANT/C₆₀ complexes were compared from stand point of stability. Increasing the number of attached ANTs, the reaction energy becomes less negative. The HOMO–LUMO energy gap of C₆₀ is slightly changed and the potential barrier of the field electron emission from its surface may be reduced upon the reaction.     

A density functional theory study on acetylene-functionalized BN nanotubes

Covalent functionalization of a zigzag boron nitride nanotube (BNNT) with acetylene has been investigated by density functional theory in terms of energetic, geometric, and electronic properties. It has been found that the most stable functionalized BNNT is the one in which the acetylene is diffused into the tube wall so that two heptagonal and two pentagonal rings are formed, releasing energy of 1.54 eV. In addition, the effect of substituting the hydrogen atoms of C₂H₂ by different functional groups including –F, –CH₂F, –CN, and –OCH₃ on the geometric and electronic properties of the BNNT has been investigated. The reaction energies are found to be in the range of ?1.03 to ?3.13 eV so that their relative magnitude order is as follows: C₂F₂ > (OCH₃)₂C₂ > C₂H₂ > (CH₂F)₂C₂ > (CN)₂C₂, suggesting that the functionalization energy is increased by increasing the electron donating character of the functional groups. Overall, chemical modification of BNNT by the studied groups results in little changes in electronic properties of the tube and may be an effective way for the purification of BNNTs.     

A theoretical study on surface modification of a nanosized BC3 tube using C2H4 and its derivatives

Chemical functionalization of a BC₃ nanotube (BC₃NT) with C₂X₄ (X = –H, –F, –CH₂F, –CN, –NH₂, –NO₂, –CH₃, and –OCH₃) was investigated by density functional theory calculations. It was found that C₂H₄ prefers to be added to a B–C bond of the tube wall. The interaction energies are calculated to be ranging from ?0.03 to ?40.32 kcal/mol, and their relative magnitude order is found to be as follows: C₂F₄ > C₂(NH₂)₄ > C₂H₄ > C₂(NO₂)₄ > C₂(OCH₃)₄ > C₂(CN₄)₂ > C₂(CH₃)₄ > C₂(CH₂F)₄. For chemically modified BC₃NTs with various functional groups, the functionalization energy can be correlated with the trend of relative electron-withdrawing or electron-donating capability of the adsorbates. The calculated density of states shows that the functionalization of BC₃NT with these functional groups (except C₂(NO₂)₄) can be generally classified as a certain type of “electronically harmless modification”. We believe that the preservation of electronic properties of BC₃NTs coupled with the enhancement of solubility may render the chemical modification to be an effective way for the purification of BC₃NTs. The insight provided by this theoretical study may also assist future development of BC₃NTs with targeted chemoselectivity through chemical functionalization.     

Ab initio molecular dynamics study for C–Br dissociation within BrH<Subscript>2</Subscript>C–C≡C<Subscript>(ads)</Subscript> adsorbed on an Ag(111) surface: a short-time Fourier transform approach

The reaction dynamics for C–Br dissociation within BrH₂C–C≡CH_(ads) adsorbed on an Ag(111) surface has been investigated by combining density functional theory-based molecular dynamics simulations with short-time Fourier transform (STFT) analysis of the dipole moment autocorrelation function. Two possible reaction pathways for C–Br scission within BrH₂C–C≡CH_(ads) have been proposed on the basis of different initial structural models. Firstly, the initial perpendicular orientation of adsorbed BrH₂C–C≡CH_(ads) with a stronger C–Br bond will undergo dynamic rotation leading to the final parallel orientation of BrH₂C–C≡CH_(ads) to cause the C–Br scission, namely, an indirect dissociation pathway. Secondly, the initial parallel orientation of adsorbed BrH₂C–C≡C_(ads) with a weaker C–Br bond will directly cause the C–Br scission within BrH₂C–C≡CH_(ads), namely, a direct dissociation pathway. To further investigate the evolution of different vibrational modes of BrH₂C–C≡CH_(ads) along these two reaction pathways, the STFT analysis is performed to illustrate that the infrared (IR) active peaks of BrH₂C–C≡CH_(ads) such as vCH₂ [2956 cm^?1(s) and 3020 cm^?1(as)], v≡CH (3320 cm^?1) and vC≡C (2150 cm^?1) gradually vanish as the rupture of C–Br bond occurs and then the resulting IR active peaks such as C=C=C (1812 cm^?1), ω-CH₂ (780 cm^?1) and δ-CH (894 cm^?1) appear due to the formation of H₂C=C=CH_(ads) which are in a good agreement with experimental reflection adsorption infrared spectrum (RAIRS) at temperatures of 110 and 200 K, respectively. Finally, the total energy profiles indicate that the reaction barriers for the scission of C–Br within BrH₂C–C≡CH_(ads) along both direct and indirect dissociation pathways are very close due to a similar rupture of C–Br bond leading to a similar transition state.     

Covalent Functionalization of Zn12O12 Nanocluster with Thiophene

Covalent functionalization of a ZnO nanocluster with thiophene molecule was studied by means of density functional theory calculations. The obtained results show that the molecule is physically adsorbed on the surface of nanocluster with adsorption energies in the range of ?0.33 to ?0.42 eV. In this study, ²η-C₄H₄S–Zn₁₂O₁₂ cluster is the most stable adsorption among all thiophene adsorption configurations. Accordingly, HOMO–LUMO energy gap of the nano-cluster is changed about 0.24 to 0.72 % using the DFT calculations. The values of charge transfer shows that π-back bonding exists for ²η and ⁵η bonding modes. Present results might be helpful to provide an effective way to modify the Zn₁₂O₁₂ properties for further applications such as generation of the new hybrid compounds.     

Computational study on the reaction mechanism of atmospheric oxidation of ethanol with ozone

The reaction of C₂H₅OH and O₃ on the singlet potential energy surface is carried out using the MP2 and CCSD(T)//MP2 theoretical approaches in connection with the 6-311++G(d,p) basis set. Three pre-reactive complexes C1, C2, and C3 are formed between ethanol and ozone at atmospheric pressure and 298.15 K temperature. With variety of the complexes, seven types of product are obtained which four types of them have enough thermodynamic stability. In thermodynamic approach, the most favor product begins with the formation of pre-reactive C2 complex and produces the CH₃CH(OH)₂ + O₂ as final adduct in a process that is computed to be exothermic by ?53.759 kcal/mol and spontaneous reaction by ?51.833 kcal/mol in Gibbs free energy. In kinetic viewpoint, the formation of CH₃COH + cis-H₂O₃ as a final adducts is the most favor path.     

Optical properties of (Z)‐2‐(2‐phenylhydrazinylidene)acenaphthen‐1(2H)‐one: a potential electron donor in organic solar cells

Electron‐donating molecules play an important role in the development of organic solar cells. (Z )‐2‐(2‐Phenylhydrazinylidene)acenaphthen‐1(2H )‐one (PDAK), C₁₈H₁₂N₂O, was synthesized by a Schiff base reaction. The crystal structure shows that the molecules are planar and are linked together forming `face‐to‐face' assemblies held together by intermolecular C—H…O, π–π and C—H…π interactions. PDAK exhibits a broadband UV–Vis absorption (200–648 nm) and a low HOMO–LUMO energy gap (1.91 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital), while fluorescence quenching experiments provide evidence for electron transfer from the excited state of PDAK to C₆₀. This suggests that the title molecule may be a suitable donor for use in organic solar cells.     

Rate constants and vibrational distributions for water-forming reactions of OH and OD radicals with thioacetic acid, 1,2-ethanedithiol and tert-butanethiol

Reactions of OH and OD radicals with CH₃C(O)SH, HSCH₂CH₂SH, and (CH₃)₃CSH were studied at 298 K in a fast-flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + CH₃C(O)SH reaction and (3.8 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + HSCH₂CH₂SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H₂S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C₂H₅)₂S reference reaction, the rate constant for the OD + (CH₃)₃CSH reaction was estimated to be (3.6 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Vibrational distributions of the H₂O and HOD molecules from the title reactions are typical for H-atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.     

Density functional study on the functionalization of BN nanotubes with nitramide

Chemical functionalization of a boron nitride nanotube (BNNT) with nitramide molecule (H₂NNO₂) has been investigated using density functional theory. It was found that the molecule prefers to be adsorbed and dissociated on a diagonal B-N bond of the tube surface so that the -NH₂ and -NO₂ groups are attached on B and N atoms, releasing energy of 0.50 eV. The results show that the functionalized BNNT is more soluble than the pristine one which may render the chemical modification process to be an effective way for purification of the BNNTs. Depending on the cleavage behavior of nitramide on the tube, HOMO/LUMO gap of the system can be either decreased or increased while the chemically modified BNNT is still a semiconductor. Furthermore, the chemical functionalization results in hindered field emission in the tube by raising the potential barrier of the electron emission.     

N2O reduction over hexagonal BN nanosheet: effects of Stone–Wales defect and carbon pair doping

Nitrous oxide (N₂O) adsorption on the pristine and Stone–Wales (SW)-defected hexagonal BN nanosheets were investigated using density functional calculations including dispersion correction. It was found that N₂O is weakly adsorbed on the pristine sheet (h-BN) through van der Waals interaction with adsorption energy of ?1.2 kcal/mol. SW-defected sheet was found to be more reactive toward N₂O molecule having no significant change in electronic properties. However, the formation of B–B and N–N bond pairs in SW-defected sheet can be avoided, if there is a C–C pair doped in sheet (C₂-SW-h-BN). In this case, a strong adsorption is found due to large adsorption energy (?23.7 kcal/mol) and short bond length compared to the SW-h-BN complex. Interestingly, it was indicated that the N₂O molecule could be reduced into the N₂ on the C₂-SW-h-BN.     

Theoretical mechanistic study on the radical-molecule reaction of CH2Br/CHBrCl with NO2

The radical-molecule reaction mechanisms of CH₂Br and CHBrCl with NO₂ have been explored theoretically at the UB3LYP/6-311G(d, p) level. The single-point energies were calculated using UCCSD(T) and UQCISD(T) methods. The results show that the title reactions are more favorable on the singlet potential energy surface than on the triplet one. For the singlet potential energy surface of CH₂Br + NO₂ reaction, the association of CH₂Br with NO₂ is found to be a barrierless carbon-to-oxygen attack forming the adduct IM1 (H₂BrCONO-trans), which can isomerize to IM2 (H₂BrCNO₂), and IM3 (H₂BrCONO-cis), respectively. The most feasible pathway is the 1, 3-Br shift with C–Br and O–N bonds cleavage along with the N–Br bond formation of IM1 lead to the product P1 (CH₂O + BrNO) which can further dissociate to give P4 (CH₂O + Br + NO). The competitive pathway is the 1, 3-H-shift associated with O–N bond rupture of IM1 to form P2 (CHBrO + HNO). For the singlet potential energy surface of CHBrCl + NO₂ reaction, there are three important reaction pathways, all of which may have comparable contribution to the reaction of CHBrCl with NO₂. The theoretically obtained major products CH₂O and CHClO for CH₂Br + NO₂ and CHBrCl + NO₂ reactions, respectively, are in good agreement with the kinetic detection in experiment.     

Theoretical study of model elementary reactions of dissociative addition of light hydrocarbons to the Ti-doped aluminide cluster Al<Subscript>12</Subscript>Ti

The potential energy surfaces (PES), energies E, and activation barriers h of elementary reactions of dissociative addition of CH₄ and C₂H₆ molecules to the Al₁₂Ti cluster with a marquee structure in the singlet and triplet states were calculated within the B3LYP approximation of the density functional theory using the 6-31G* basis set. The first stage of the reaction Al₁₂Ti + CH₄ leads to the adsorption complex CH₄ · Al₁₂Ti with the R(TiC) distance of ～2.4 Å. The methane molecule is coordinated as a tridentate ligand the singlet state and as a bidentate ligand in the triplet state, although both coordination modes are close in energy. In the transition state, the CH₄ molecule is coordinated through its active C-H bond to an inclined Ti-Al edge of the cluster, and the C-H bond is significantly elongated and weakened. The activation barrier height h referenced to the CH₄ complex is ～9 and ～19 kcal/mol for the singlet and triplet, respectively, and that referenced to the primary products Al₁₂Ti(CH₃)(H) is ～21 kcal/mol. The barrier to migration of the CH₃ group around the metal cluster is estimated at ～10 kcal/mol. At the initial stage of the reaction Al₁₂Ti + C₂H₆, two types of C₂H₆ · Al₁₂Ti adsorption complexes are formed. In one of them, the ethane molecule is coordinated through a methyl group (as the methane molecule); and in the other type, the coordination is through the C-C bond. This reaction can proceed through two paths by means of insertion into C-H or C-C bonds to give Al₁₂Ti(C₂H₅)(H) or Al₁₂Ti(CH₃)₂, respectively. The second path is impeded by a high barrier (～30 kcal/mol) and is possible, if at all, only at high temperatures. Conversely, the insertion into a C-H bond in ethane is somewhat more favorable than in methane. Analogously, the PES of addition of the second methane molecule to Al₁₂Ti(CH₃)(H) was calculated. The second molecule is adsorbed and dissociates by the same mechanism as the first CH₄ molecule, but with somewhat lower barriers and energy effect of formation of Al₁₂Ti(CH₃)₂(H)₂. The addition of propane and longer hydrocarbons is briefly considered. The results are compared with the results of previous analogous calculations of the PES of related reactions of dissociative adsorption of dihydrogen on the Al₁₂Ti cluster, which are more exothermic, have lower barriers, and can occur under milder conditions.     

Direct Formation of Cycloadducts Between Fullerenes and Amino Acids Through Electron-Transfer Processes

Abstract

The reactions of [60]fullerene and amino acids in the absence of aldehyde in o-dichlorobenzene (ODCB) at 150 °C have been investigated. Fulleropyrrolidines 1 [C₆₀(CH₂N(CH₃)CHC₆H₂(NO₂)₃)], 2 [C₆₀(CH₂N(CH₃)CH₂)], 3 [C₆₀(CH₂NHCH₂)], and 5a–b [C₆₀(RCHNHCHR), R?CH₃ (5a), R?CH₂Ph (5b)] were obtained in moderate yields from the reactions of C₆₀ and corresponding amino acids. The reaction of C₇₀ and N-methylglycine in the absence of aldehyde was also studied and was found to give the positional isomers of N-methyl[70]fulleropyrrolidines 6 (1,9-isomer) and 7(7,8-isomer). All products were fully characterized by ultraviolet–visible, Fourier transform–infrared (FT-IR), NMR, and mass spectrometry. The reactions were also carried out in the dark to exclude the possible interference of the photoinduced reactions, and almost the same yields of products were obtained.     

Rehybridization of C2H2 chemisorbed on W(110)

Chemisorption of C₂H₂ on W(110) has been studied by high resolution electron energy low spectroscopy. At low coverages the molecule dissociates, while at thigh coverage C₂H₂ is di-σ adsorbed with a CC bond order of 0.25 and a CH bond angle of. ≈ 103°.     

Constructing a novel nonlinear optical materials: substituents and heteroatoms in π-π systems effect on the first hyperpolarizability

By doping π-π systems with Li atom, a series of Li@sandwich configuration and Li@T-shaped configuration compounds have been theoretically designed and investigated using density functional theory. It is revealed that energy gaps (E _gap) between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of all compounds are in a range of 0.4–0.9 ev. When Li atom is introduced into different sandwich configuration π-π systems (C₆₀-toluene, C₆₀-fluorobenzene, C₆₀-phenol, C₆₀-benzonitrile), Li@C₆₀-benzonitrile exhibits considerable first hyperpolarizability as large as 19,759 au, which is larger by about 18,372–18,664 au than those of other compounds. When Li atom is introduced into different T-shaped configuration π-π systems (C₆₀-pyridine, C₆₀-pyrazine, C₆₀-1, 3, 5-triazine, C₆₀-pyridazine), Li@C₆₀-pyridazine is found to present largest first hyperpolarizability up to 67,945 au in all compounds. All compounds are transparency in the deep ultraviolet spectrum range. We hope that this study could provide a new idea for designing nonlinear optical materials using π-π systems as building blocks.     

Theoretical study on the gas phase reaction mechanism of acetylene with nitrous oxide

The reaction mechanism of C₂H₂ and N₂O on the singlet potential energy surface is investigated in this study, at the B3LYP/6-311++G(3df,3pd), MP2/6-311++G(d,p), and CCSD(T) levels of theory. We have obtained three kinds of products in both methods, B3LYP and MP2, which have enough thermodynamic stability. The results reveal that the product P1, CH₂CO + N₂, is spontaneous and exothermic with ?86.176 and ?83.149 kcal/mol in Gibbs free energy and enthalpy of reaction at the MP2 level, respectively. Hence, the product P1 is thermodynamically the most favored adduct of the C₂H₂ + N₂O gas phase reaction at atmospheric pressure and 298.15 K temperature.     

DFT study on the adsorption and dissociation of hydrogen sulfide on MgO nanotube

The adsorption of a H₂S molecule on the surface of an MgO nanotube was investigated using density functional theory. It was found that H₂S molecule can be associatively adsorbed on the tube surface without any energy barrier or it can be dissociated into –H and –SH species overcoming energy barrier of 4.03–7.77 kcal/mol. The associative adsorption is site selective so that the molecule is oriented in such a way that the sulfur atom was linked to an Mg atom. The HOMO–LUMO energy gap of the tube has slightly changed upon associative adsorption, while they were significantly influenced by dissociation process. Especially, the highest occupied molecular orbital of the tube shifts to higher energies which can facilitate electron emission current from the tube surface. Also, energy gap of the tube dramatically decreased by about 0.93–1.05 eV which influences the electrical conductivity of the tube.     

Theoretical investigation of carboranylpyrrole structures and the thermal resistance and conducting properties of carboranylpyrrole polymers

The carboranylpyrrole polymers are functional materials with superior thermal resistance and conducting performances. The carboranylpyrrole structures and Laplacian bond order (LBO) of carborane moiety, as well as the thermal resistance and conducting properties of carboranylpyrrole dimers or polymers, were investigated theoretically. The ¹¹B NMR chemical shifts of 3-(2-methyl-o-carboranyl)alkyl-1H-pyrrole monomers (CP-1 to CP-5) were calculated and analyzed. The average LBO values of some characteristic chemical bonds in the carborane cages of CP-1 to CP-5 molecules were calculated. It is found that the average LBO values of carborane moieties change slightly with the increase in alkyl chain length. The temperature resulting in about 15–20 % weight loss for CP-1, CP-3, CP-4 and CP-5 polymers is predicted to be more than 700 °C. Apart from the C–C bonds in carborane moieties of 3-(2-R-o-carboranyl)propyl-1H-pyrrole (R = CH₂OH, CH₂OCH₃, CN, COCl, Ph) substituents, the LBO values of other bonds in these cages change slightly relative to that in the molecule of 3-(2-methyl-o-carboranyl)propyl-1H-pyrrole (CP-3). The C–C bond LBO values in the carborane cages of these substituents with electron-donating groups (R = CH₂OH, CH₂OCH₃) are bigger than that in CP-3, while those values in those substituents with electron-withdrawing groups (R = CN, COCl, Ph) are smaller than that in CP-3. The polymerization activity calculated for CP-1 to CP-5 monomers increases with the increase in alkyl chain length. The calculated orbital energy gap (?E _LUMO?HOMO) of CP-1 to CP-5 dimers decreases with the increase in alkyl chain length, and accordingly, the electronic conductivity has the potential to increase. In addition, the calculated band gaps of CP-1 to CP-5 dimers cell models also decrease with the increase in alkyl chain length.     

Chlorination of charged buckyballs: reactions of C60x+ cations (x = 1–3) with Cl2, CCl4, CDCl3, CH2Cl2, and CH3Cl

The chlorination of singly and multiply charged C₆₀ cations has been investigated with the selected-ion flow tube technique. Observations are reported for the reactions of C₆₀^·+, C₆₀²⁺ and C₆₀^·3+ with Cl₂, CCl₄, CDCl₃, CH₂Cl₂ and CH₃Cl at room temperature (295 ± 2 K) in helium at a total pressure of 0.35 ± 0.02 Torr. C₆₀^·+ and C₆₀²⁺ were observed not to chlorinate, or react in any other way, with these five molecules. Chlorine also did not react with C₆₀^·3+, but bimolecular chloride transfer and electron transfer reactions, reactions that result in charge reduction/charge separation, were observed to occur with CCl₄, CDCl₃, CH₂Cl₂ and CH₃Cl. Chloride transfer was the predominant channel seen with CCl₄, CDCl₃ and CH₂Cl₂ while electron transfer dominates the reaction with CH₃Cl. These results are consistent with trends in chloride affinity and ionization energy. The reluctant chlorination of the first two charge states of C₆₀ is attributed to the energy required to distort the carbon cage upon bond formation, while the observed chloride transfer to C₆₀^·3+ is attributed to the greater electrostatic interactions with this ion.     

Theoretical study on the gas phase reaction of acrylonitrile with atomic hydrogen

The complex potential energy surface of the H + CH₂=CHCN reaction has been investigated at the BMC-CCSD level based on the geometric parameters optimized at the BHandHLYP/6-311++G(d,p) level. This reaction is revealed to be one of the significant loss processes of acrylonitrile. The BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism confirms that H can attack on the C=C double bond or C and N atom of –CN group to form the chemically activated adducts IM1 (CH₃CHCN), IM2 (CH₂CH₂CN), IM3′ (CH₂=CHCHN) and IM5 (CH₂=CHCNH), and direct H-abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been carried out using Rice–Ramsperger–Kassel–Marcus theory with tunneling correction. IM1 (CH₃CHCN) formed by collisional stabilization is the major product at the 760 Torr pressure of H₂ and in the temperature range (200–1,600 K); whereas the production of IM2 (CH₂CH₂CN) is the main channel at 1,600–3,000 K. The calculated rate constants are in good agreement with the experimental data.