The reaction mechanism underlying the hypergolic reaction of pure monomethylhydrazine (MMH) with 1-chloro-1,1-dinitro-2-(N-chloroamidino)ethane (CDNCE) was theoretically investigated with the density functional theory method. We identified two key atomistic level factors that affect ignition delay: (1) exothermicity for the formation of aerosol mCDNCE·nMMH complexes (m, n = 1, 2). The most cost-effective form was found to be 2CDNCE·MMH with the highest energy release (releasing energy: 23.4 kcal/mol), indicating that the oxidizer-rich form is favorable. These complexes contributed the most to heat gathering and temperature increases in the system at the beginning of all reactions. (2) For the initial reaction of MMH with CDNCE, the SN2 mechanism was preferred. The activation barrier of the primary reactions was calculated to be 27.4 kcal/mol, which is also the rate-limiting step of this path. Because the rate of formation of NO2 was four orders of magnitude lower than the SN2 reaction at room temperature, the effect of MMH with NO2 was less significant at temperatures below 800 K. Thus, we consider the ignition reaction of MMH with CDNCE to be well characterized.

•A transient model for passive DMFC is developed to study cell orientation effect.•Vertical orientation has higher energy density than horizontal except high current.•Roles of AMPL and CMPL are different with different cell orientations.•Horizontal orientation is more sensitive to methanol crossover.A transient model for passive direct methanol fuel cell (DMFC) is developed to investigate the effect of cell orientation and operating condition. The results show that the passive DMFC with vertical orientation has better performance than the horizontal one, except the case of high current density, because a large amount of water produced in cathode is hard to be removed in vertical orientation, which is easier for horizontal orientation due to gravity. The passive DMFC with horizontal orientation is sensitive to methanol crossover, and moderate current density or voltage is necessary to ensure high energy efficiency. The anode micro-porous layer (MPL) plays an important role in reducing the rate of methanol crossover by providing flow resistance. The MPL in cathode has a significant effect on water transport by enhancing the water back-flow from cathode to anode, which prevents water removal. Therefore, the anode MPL and cathode MPL have different effects on horizontal orientation and vertical orientation. Additionally, the size of fuel tank can improve the energy density by providing more fuel, and the effect on fuel efficiency and energy efficiency is a bit obvious in vertical orientation than horizontal orientation.

Fluorination has been instrumental for tuning the properties of several two-dimensional (2D) materials, including graphene, h-BN, and MoS2. However, its potential application has not yet been explored in 2D silicon carbide (SiC), a promising material for nanoelectronic devices. We investigate the structural, electronic, and magnetic properties of fully and partially fluorinated 2D SiC sheets and nanoribbons by means of density functional theory combined with cluster expansion calculations. We find that fully fluorinated 2D SiC exhibits chair configurations and a nonmagnetic semiconducting behavior. Fluorination is shown to be an efficient approach for tuning the band gap. Four ground states of partially fluorinated SiC, SiCF2x with x = 0.0625, 0.25, 0.5, 0.75, are obtained by cluster expansion calculations. All of them exhibit nanoroad patterns, with the x = 0.5 structure identified as the most stable one. The x = 0.0625 structure is a nonmagnetic metal, while the other three are all ferromagnetic half-metals, whose properties are not affected by the edge states. We propose an effective approach for modulating the electronic and magnetic behavior of 2D SiC, paving the way to applications of SiC nanostructures in integrated multifunctional and spintronic nanodevices.

The charge-transport parameters in three 4,10-dihalogenated anthanthrones (AAOs) are investigated by means of density functional theory (DFT) and molecular dynamics (MD) calculations. Our calculations point to similar hole and electron reorganization energies for each molecule. Significant electronic couplings and bandwidths (particularly for electron transport) are found along the parallel π–π stacking directions in all the dihalogenated AAO crystals. The calculated effective masses are small or moderate for both holes and electrons. Especially for the iodinated AAO crystals, remarkable ambipolar charge transport can be anticipated due to the smallest and similar effective masses for holes and electrons (both are around 1.0 m0). In addition, due to the presence of two small effective masses, two-dimensional charge transport would take place for electrons in the chlorinated AAO crystal and for both holes and electrons in the iodinated AAO crystal. Also, our calculations reveal large nonlocal electron–phonon couplings along the π-stacks in the brominated AAO and, in particular, the chlorinated AAO crystals, which can further improve the balance in transport of holes and electrons.

•A comprehensive multiphase model for passive DMFC is developed.•Variable contact angle effect of electrode due fabrication is studied.•Increasing contact angle along flow direction of methanol reduces crossover.•DL/MPL and MPL/CL interfacial transport resistance is critical.•Results shed light on development of novel electrode with variable contact angle.In this study, a multiphase passive direct methanol fuel cell (DMFC) model is developed to study the effect of micro porous layer (MPL) insertion, and the variable contact angle effects due to the different fabrication processes of diffusion layer (DL) and MPL are also investigated in details. It is found that with the contact angle increasing along the flow direction of methanol in anode DL (ADL), the liquid always needs to flow from a more hydrophilic region to a more hydrophobic region, leading to less methanol crossover. A higher ADL contact angle generally leads to more methanol crossover, although it increases the flow resistance at the inlet, the mass transport resistance at the DL/MPL interface is reduced, and the capillary driven flow is also enhanced inside the DL. However, since MPL is often a very thin layer compared with GDL, it could act as a mass transfer barrier mainly because of the contact angle differences across the MPL/DL and MPL/CL interfaces, which is the dominating factor determining the MPL function. The results also shed the light on the development of novel electrode with variable contact angle based on different fabrication processes.

•A transient multiphase model for passive DMFC is developed.•Effects of current, voltage, MPL and methanol feeding condition are investigated.•Voltage needs to be moderate to ensure energy efficiency and density.•AMPL and CMPL can all reduce methanol crossover, but AMPL is more important.•Fuel tank size has considerable effect on energy density, but not energy efficiency.By developing a transient multiphase model for passive direct methanol fuel cell (DMFC), the effects of operating current density, voltage, micro-porous layer (MPL) and methanol feeding condition are comprehensively investigated for the whole operating processes (fuel tank from full to empty). It is found that for all the operating conditions, it is necessary to operate at moderate current density or voltage to limit the methanol crossover and ensure the energy conversion efficiency. The MPL in anode is needed to provide sufficient flow resistance at the MPL/gas diffusion layer (GDL) interface to improve the fuel efficiency. Although the cathode MPL can strengthen the convective transport of methanol from cathode to anode, its effect on reducing methanol crossover is less significant than the anode MPL. If the energy density is the most important factor, it is suggested to operate with sufficiently high methanol feeding concentration; and if the fuel and energy efficiencies have the priority, the methanol feeding concentration needs to be moderate. Increasing the size of fuel tank generally improves the energy density, but has negligible effect on the fuel and energy efficiencies.

Bidentate directing group (DG) strategy is a promising way to achieve sp2 and more inert sp3 C–H bond activations in transition metal (TM) catalysis. In this work, we systematically explored the assisting effects exerted by bidentate DGs in the C–H bond activations. Through DFT calculations and well-defined comparative analysis, we for the first time unified the rationale of the reactivity promoted by bidentate DG in sp2 and sp3 C–H activations, which are generally consistent with available experimental discoveries about the C–H activation reactivity up to date. In addition to the general rationale of the reactivity, the assisting effects of several typical bidentate DGs were also quantitatively evaluated and compared to reveal their relative promoting ability for C–H activation reactivity. Finally, the effect of the ligating group charge and the position of the ligating group charge in bidentate DGs were also investigated, based on which new types of DGs were designed and proposed to be potentially effective in C–H activation. The deeper understanding and new insight about the bidentate DG strategy gained in this work would help to enhance its further experimental development in sp2 and sp3 C–H bond activations.

Structures and nonlinear optical(NLO) properties of eleven new Lin-Pm(n=1–5) species were investigated in detail with the help of ab initio computation, in which one to the maximum five Li atoms are doped over the polycyclic π-conjugated pentacene. These Li-doped pentacene systems exhibit large adsorption energies(ca. 107.0–141.3 kJ/mol) and considerable first hyperpolarizabilities(even up to 4.1×104 a.u.), where the number of Li atoms, the doping site, and the distance between the neighboring Li atoms have important impacts on the β0 value. In the doped pentacene systems with less Li atoms(one or two), the improvement of β0 value can be attributed to the simple transfer of the charge from Li atom to pentacene. Differently, doped more Li atoms(three to five) can cause not only charge transfer but also excess electron, and this cooperation can endow the doped systems with the much larger first hyperpolarizabilities. These fascinating findings are advantageous for the design of new NLO materials based on the intriguing polycyclic π-conjugated systems.

DFT calculations have been carried out to study the mechanism of Cu(AcO)2-catalyzed N-alkylation of amino derivatives with primary alcohols. The calculations indicate that tBuOK is necessary for the generation of the active catalyst from Cu(AcO)2 and that the catalytic cycle involves three sequential steps: (1) Cu-catalyzed alcohol oxidation to give the corresponding aldehyde and copper hydride, (2) aldehyde-amine condensation to generate an imine, (3) imine reduction to yield the expected N-alkylation secondary amine product and to regenerate the active catalyst. Based on the comparison of different reaction pathways, we conclude that the outer-sphere hydrogen transfer in a stepwise manner is the most favorable pathway for both alcohol oxidation and imine reduction. Thermodynamically, alcohol oxidation and imine formation are all uphill, but imine reduction is downhill significantly, which is the driving force for the catalytic transformation. Using the energetic span model, we find that the turnover frequency-determining transition state (TDTS) and the turnover frequency-determining intermediate (TDI) are the hydride transfer transition state for imine reduction and the active catalyst, respectively. The calculated turnover frequency (TOF) roughly agrees with the experimental observation and, therefore, further supports the validity of the proposed hydrogen transfer mechanism.Keywords: amino derivatives; Cu(AcO)2; DFT calculations; hydrogen transfer mechanism; N-alkylation reaction; primary alcohols; tBuOK

The strategy using N,N-bidentate directing groups is a promising way to achieve selective C(sp2)–H activation inaccessible by that of monodentate directing groups. Herein, through theoretical calculations, we present a rationale behind this strategy, which deciphers its key roles in C–H activation promoted by Ni, Pd, Ru, and Cu. The calculations reveal two key points: (a) Between the two coordination sites of the N,N-bidentate directing group, the proximal one influences more the C–H activation barrier ΔG‡, whereas the distal site affects more the free energy change ΔG relevant to the substrate coordination. (b) Enlarging/shrinking the chelation ring can exert different effects on the reactivity, depending on the metal identity and the ring size. Importantly, our computational results are in full agreement with previous experimental findings concerning reactivity. Furthermore, a prediction about the unprecedented reactivity from our theory is confirmed by our experiments, lending more credence to the rationale and insights gained in this study.Keywords: C(sp2)−H activation; coordination free energy; density functional theory; N,N-bidentate directing group; reaction barrier; transition metal

Based on (6, 0) zigzag carbon nanotubes (ZCNTs), a Stone–Wales defect ring ([5.7]3) is constructed at one end of the ZCNTs, forming a novel nanostructure [5.7]3ZCNT. The introduction of [5.7]3 breaks the centrosymmetry of the nanotube and remarkably changes electronic and magnetic properties of the nanotube. Unlike the (6, 0)ZCNT which has an open-shell singlet ground state, the [5.7]3ZCNT has a closed-shell singlet ground state with a large dipole moment, polarizability, and first hyperpolarizability. Interestingly, the [5.7]3ZCNT itself has a donor–π–acceptor framework, in which the Stone–Wales defect ring serves as an electron donor (D) while the zigzag nanotube works as an electron acceptor (A) and a conjugated bridge (π). Moreover, increasing both the tube diameter and tube length could enhance second-order nonlinear optical (NLO) responses, with the former being more effective than the latter.

Developing efficient dehydrogenation is critical to understanding organic hydride hydrogen storage. The catalytic mechanism of the pH-dependent acceptorless-alcohol-dehydrogenation in aqueous solution catalyzed by a novel [C,N] cyclometalated Cp*Ir-complex, [IrIII(Cp*)-(4-(1H-pyrazol-1-yl-κN2)benzoic acid-κC3)(H2O)]2SO4, has been investigated using density functional theory (DFT) with the M06 dispersion-corrected functional. Using water as the solvent with liberation of dihydrogen represents a safe and clean process for such oxidations. The overall catalytic cycle has been fully characterized. The pre-catalyst AIr first reacts with the ethanol in basic solution to generate an active hydride complex DIrvia an inner-sphere mechanism, involving the hemi-decoordination of [C,N] ligand followed by the β-H elimination. Subsequently, the complex DIr interacts with the protons in acid solution to generate H2 molecules, which is a downhill process nearly without an energy barrier. The present theoretical results have shown that both the hydroxyl in basic solution and the proton in acidic solution play a crucial role in promoting the whole catalytic cycle. Therefore, our results theoretically demonstrated a significant dependence of the reaction system studied on pH value. The present study also predicts that the FIr (at the first triplet excited state, T1) formed from DIr under laser excitation can catalyze the dehydrogenation of ethanol. Remarkably, the replacement of Ir by Ru may yield an efficient catalyst in the present system.

Using cinchona alkaloid-derived primary amine as catalyst and benzoic acid as co-catalyst, Michael-type addition reactions between enolizable carbonyl compounds and nitroalkenes have been extensively studied; however, our understanding of the mechanism is far from complete. In this paper, a theoretical study is presented for the Michael addition reaction between trans-1-nitro-2-phenylethylene and 2-methylpropionaldehyde catalyzed by 9-epi-QDA and benzoic acid. By performing DFT and ab initio calculations, we have identified a detailed mechanism. The calculations indicated that four continuous steps are involved in the overall reaction: (1) the formation of an iminium intermediate, (2) an addition reaction between the iminium and trans-1-nitro-2-phenylethylene, (3) the proton transfer process, and (4) hydrolysis and regeneration of the catalyst. The rate-determining step is the second proton transfer from the amine group to β-carbon of trans-1-nitro-2-phenylethylene, and the enantioselectivity is also controlled by this step. The calculated results provide a general model that explains the mechanism and enantioselectivity of the title reaction.

A range of novel octahedral iron(IV)–nitrido complexes with the TMC ligand (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) in the equatorial plane and one axial ligand trans to the nitrido have been designed theoretically, and a systematic comparative study of their geometries, electronic properties, and reactivities in hydrogen atom abstraction reactions regarding the iron(IV)–oxo and −sulfido counterparts has been performed using density-functional theory methods. Further, the relative importance of the axial ligands on the reactivity of the iron(IV)–nitrido systems is probed by sampling the reactions of CH4 with [FeIV═N(TMC)(Lax)]n+, (Lax = none, CH3CN, CF3CO2–, N3–, Cl–, NC–, and SR–). As we find, one hydrogen atom is abstracted from the methane by the iron(IV)–nitrido species, leading to an FeIII(N)–H moiety together with a carbon radical, similar to the cases by the iron(IV)–oxo and −sulfido compounds. DFT calculations show that, unlike the well-known iron(IV)–oxo species with the S = 1 ground state where two-state reactivity (TSR) was postulated to involve, the iron(IV)–nitrido and −sulfido complexes stabilize in a high-spin (S = 2) quintet ground state, and they appear to proceed on the single-state reactivity via a dominantly and energetically favorable low-lying quintet spin surface in the H-abstraction reaction that enjoys the exchange-enhanced reactivity. It is further demonstrated that the iron(IV)–nitrido complexes are capable of hydroxylating C–H bond of methane, and potential reactivities as good as the iron(IV)–oxo and −sulfido species have been observed. Additionally, analysis of the axial ligand effect reveals that the reactivity of iron(IV)–nitrido oxidants in the quintet state toward C–H bond activation enhances as the electron-donating ability of the axial ligand weakens.

The triplet δ-mechanism different from the previously reported ones, i.e., the π-channel with the unoccupied π*xz/yz (FeO) orbital and the σ-channel involving the unoccupied α-spin Fe-σ*z2 orbital, has been theoretically described for the methane hydroxylation by [FeIV = O(TMC)(SR)]+ and its derivative [FeIV = O(TMC)(OH)]+ complex for the first time, and we have undertaken a detailed DFT study on the nature of this state by probing its geometry, electronic property and reactivity in comparison to all other possibilities. DFT calculations indicate that the electron transfer for the 3δ-channel from the σC–H orbital of the substrate to the final acceptor σ*x2−y2 orbital of the catalyst occurs through a complex mechanism, which is initiated by the original α-spin electron transfer from the π* orbital of the catalyst to the σ*x2−y2 orbital, where the α-spin electron from the σC–H orbital of the substrate shifts to the just empty α-spin π* orbital of the catalyst via the O-px/y based π*xz/yz-orbital concomitantly. It is also found that the electron-donating ability of the axial ligand could influence the reaction channels, evident by the distinction that the electron-deficient F− and CF3CO2− ligands react via the 3σ-channel, whereas the electron-rich SR− and OH− ligands proceed by the 3δ-channel. With respect to reactivity, the 3δ-pathway has a comparable barrier to the 3π and 5π-pathways, which may offer a new approach for the specific control of C–H bond activation by the iron(IV)-oxo species.

•The original and interesting concept of octupolar electride (Li@36Adz) is first proposed for nonlinear optics.•Li@36Adz has a very large first hyperpolarizability, up to 1787×10-30 esu at the restricted open-shell second-order Møller–Plesset (ROMP2) level.•Due to the low ionization potential (1.84 eV), Li@36Adz can be seen as superalkalies.Based on the synthesized H@36Adz (36Adz = 36 adamanzane), a new class of three-dimensional (3D) octupolar molecule Li@36Adz with electride characteristics is first designed and studied with theoretical tools, in which the electron of the encapsulated Li atom is extruded from the cage of 36Adz forming diffused excess electron. Due to S4 symmetry, Li@36Adz only has the octupolar hyperpolarizability (βJ=3) up to 1787 × 10−30 esu at the restricted open-shell second-order Møller–Plesset (ROMP2) level, whose β is about 1787 times more than that (1 × 10−30 esu) of its analogue (H@36Adz). Interestingly, we find that both Li@36Adz has a very low ionization potential (1.84 eV) which can be seen as superalkalies. The present investigations will enrich the concept of 3D octupolar molecules for high-performance NLO materials and offer a method to construct superalkalies.The original and interesting concept of octupolar electride (Li@36Adz) is proposed for nonlinear optics. And this class of molecules exhibits giant first hyperpolarizability.

Friedel–Crasfts alkylation reactions of α,β-unsaturated butyric aldehydes with N,N-dimethyl-3-anisidine catalyzed by a (2S,5S)-5-benzyl-2-tert-butyl-3-methylimidazolidin-4-one HCl salt have been carried out at the PCM(CH2Cl2)/B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level. Three reaction processes have been characterized: (I) the formation of an iminium ion intermediate; (II) the 1,4-iminium addition of the iminium ion; and (III) the hydrolysis of the addition product. Moreover, Path 1-1 is the favorable channel in the formation of the iminium ion. From the point of view of energy, the enantioselectivity is controlled by the carbon–carbon bond formation step that is involved in both the intermediate M4 and the transition state TS4. The highest energy barrier of the reaction is the H2 proton transfer from the O10 atom of a water molecule to the N1 atom of the catalyst in the hydrolysis process, which is 23.4 kcal/mol. The presented calculated results may be helpful in understanding the experimental product distribution for the title reaction, and provide a general model to help explain the mechanisms of similar reactions.

The conversion of benzene to phenol by high-valent bare FeO2+ was comprehensively explored using a density functional theory method. The conductor-like screen model (COSMO) was used to mimic the role of solvent effect with acetonitrile chosen as the solvent. Two radical mechanisms and one oxygen insertion mechanism were tested for this conversion. The first radical mechanism can also be named as the concerted mechanism in which the hydrogen-atom abstraction process is accomplished via a four-centered transition state. The second radical mechanism is initiated by a direct hydrogen-atom abstraction with a collinear C–H–O transition structure. It is actually the same as the well-accepted rebound mechanism for the C–H bond activation by heme and nonheme iron-oxo catalysts. The third is an oxygen insertion mechanism which is essentially an aromatic electrophilic attack leading to an arenium σ-complex intermediate. The formation of a precomplex with an η4 coordinate environment in the first radical mechanism is energetically more favorable. However, the relatively lower activation energy barrier of the oxygen insertion mechanism compared to the radical ones makes it highly competitive if the FeO2+ collides with benzene in the proper orientation. The detailed potential energy surfaces also indicate that the second radical mechanism, i.e., the benzene C–H bond activation through the rebound mechanism, is less favorable. This thorough theoretical study, especially the electronic structure analysis, may offer very important clues for understanding and studying C–H bond activation by iron-based catalysts and enzymatic reactions in protein active pockets.

Comprehensive density functional theory computations on substrate hydroxylation by a range of nonheme iron(IV)–oxo model systems [FeIV(O)(NH3)4L]+ (where L = CF3CO2−, F−, Cl−, N3−, NCS−, NC−, OH−) have been investigated to establish the effects of axial ligands with different degrees of electron donor ability on the reactivity of the distinct reaction channels. The results show that the electron-pushing capability of the axial ligand can exert a considerable influence on the different reaction channels. The σ-pathway reactivity decreases as the electron-donating ability of the axial ligand strengthens, while the π-pathway reactivity follows an opposite trend. Moreover, the apparently antielectrophilic trend observed for the energy gap between the triplet π- and quintet σ-channel (ΔG(T–Q)) stems from the fact that the reaction reactivity can be fine-controlled by the interplay between the exchange-stabilization benefiting from the 5TSH relative to the 3TSH by most nonheme enzymes and the destabilization effect of the orbital by the anionic axial ligand. When the former counteracts the latter, the quintet σ-pathway will be more effective than the other alternatives. Nevertheless, when the dramatic destabilization effect of the orbital by a strong binding axial σ-donor ligand like OH− counteracts but does not override the exchange-stabilization, the barrier in the quintet σ-pathway will remain identical to the triplet π-pathway barrier. Indeed, the axial ligand does not change the intrinsic reaction mechanism in its respective pathway; however, it can affect the energy barriers of different reaction channels for C–H activation. As such, the tuning of the reactivity of the different reaction channels can be realised by increasing/decreasing the electron pushing ability.

Molecular dynamics (MD) simulations were carried out to study the behavior of human receptor molecule in the hemagglutinin (HA) of 1918 and 2009 H1N1 influenza viruses respectively. The 2009 HA model was obtained by virtually mutating the 1918 HA crystal structure based on A/Mexico City/MCIG01/2009(H1N1) segment 4 sequence. We found that human receptor molecule has no binding preference between the 2009 HA and the 1918 HA. In addition, among the four sugar moieties in the human receptor molecule, sialic acid contributes the most to the electrostatic and non-polar interaction energy during binding. Furthermore, the hydrogen bonds between sialic acid and the surrounding residues in 1918 HA are preserved in 2009 HA. We also found that the mutated residues contribute to a more favorable binding of hemagglutinin to the human receptor molecule.

The MP2 frequency-dependent β values are estimated by using the multiplicative approximation. The frequency dispersion is found to be strong. For the MP2 frequency-dependent β values, the more pronounced dependence on the petal number (n) of β (−2ω; ω, ω) and β (−ω; ω, 0) are shown.

•A transient model for passive vapor-feed DMFC is developed.•Cathode water recovery is critical when neat methanol vapor is supplied.•Cathode MPL is beneficial to water recovery from cathode to anode.•Increasing current and membrane thickness help reduce methanol crossover.•Decreasing vaporizer open ratio generally has positive impact.A transient model is presented to investigate the transport phenomena for passive vapor-feed direct methanol fuel cell (DMFC). The pervaporation membrane and vapor transport layer are considered for the formation and transport of methanol vapor, respectively. We attempt to provide insight into the transient mass transport characteristics of DMFCs by testing different operation conditions, including current density, open area ratio of the vaporizer, and membrane thickness. The results show that the methanol crossover rate and water transport from the cathode to the anode are the key factors for improving the cell performance, and indicate that fuel efficiency, energy efficiency and energy density of the DMFCs are improved by increasing current density, decreasing open ratio of the vaporizer or increasing membrane thickness due to the reduced methanol crossover rate. The cathode micro-porous layer (MPL) is useful in enhancing water recovery flux and decreasing water losses.

The charge-transport parameters in three 4,10-dihalogenated anthanthrones (AAOs) are investigated by means of density functional theory (DFT) and molecular dynamics (MD) calculations. Our calculations point to similar hole and electron reorganization energies for each molecule. Significant electronic couplings and bandwidths (particularly for electron transport) are found along the parallel π–π stacking directions in all the dihalogenated AAO crystals. The calculated effective masses are small or moderate for both holes and electrons. Especially for the iodinated AAO crystals, remarkable ambipolar charge transport can be anticipated due to the smallest and similar effective masses for holes and electrons (both are around 1.0 m0). In addition, due to the presence of two small effective masses, two-dimensional charge transport would take place for electrons in the chlorinated AAO crystal and for both holes and electrons in the iodinated AAO crystal. Also, our calculations reveal large nonlocal electron–phonon couplings along the π-stacks in the brominated AAO and, in particular, the chlorinated AAO crystals, which can further improve the balance in transport of holes and electrons.

The conversion of benzene to phenol by high-valent bare FeO2+ was comprehensively explored using a density functional theory method. The conductor-like screen model (COSMO) was used to mimic the role of solvent effect with acetonitrile chosen as the solvent. Two radical mechanisms and one oxygen insertion mechanism were tested for this conversion. The first radical mechanism can also be named as the concerted mechanism in which the hydrogen-atom abstraction process is accomplished via a four-centered transition state. The second radical mechanism is initiated by a direct hydrogen-atom abstraction with a collinear C–H–O transition structure. It is actually the same as the well-accepted rebound mechanism for the C–H bond activation by heme and nonheme iron-oxo catalysts. The third is an oxygen insertion mechanism which is essentially an aromatic electrophilic attack leading to an arenium σ-complex intermediate. The formation of a precomplex with an η4 coordinate environment in the first radical mechanism is energetically more favorable. However, the relatively lower activation energy barrier of the oxygen insertion mechanism compared to the radical ones makes it highly competitive if the FeO2+ collides with benzene in the proper orientation. The detailed potential energy surfaces also indicate that the second radical mechanism, i.e., the benzene C–H bond activation through the rebound mechanism, is less favorable. This thorough theoretical study, especially the electronic structure analysis, may offer very important clues for understanding and studying C–H bond activation by iron-based catalysts and enzymatic reactions in protein active pockets.

Based on (6, 0) zigzag carbon nanotubes (ZCNTs), a Stone–Wales defect ring ([5.7]3) is constructed at one end of the ZCNTs, forming a novel nanostructure [5.7]3ZCNT. The introduction of [5.7]3 breaks the centrosymmetry of the nanotube and remarkably changes electronic and magnetic properties of the nanotube. Unlike the (6, 0)ZCNT which has an open-shell singlet ground state, the [5.7]3ZCNT has a closed-shell singlet ground state with a large dipole moment, polarizability, and first hyperpolarizability. Interestingly, the [5.7]3ZCNT itself has a donor–π–acceptor framework, in which the Stone–Wales defect ring serves as an electron donor (D) while the zigzag nanotube works as an electron acceptor (A) and a conjugated bridge (π). Moreover, increasing both the tube diameter and tube length could enhance second-order nonlinear optical (NLO) responses, with the former being more effective than the latter.

Comprehensive density functional theory computations on substrate hydroxylation by a range of nonheme iron(IV)–oxo model systems [FeIV(O)(NH3)4L]+ (where L = CF3CO2−, F−, Cl−, N3−, NCS−, NC−, OH−) have been investigated to establish the effects of axial ligands with different degrees of electron donor ability on the reactivity of the distinct reaction channels. The results show that the electron-pushing capability of the axial ligand can exert a considerable influence on the different reaction channels. The σ-pathway reactivity decreases as the electron-donating ability of the axial ligand strengthens, while the π-pathway reactivity follows an opposite trend. Moreover, the apparently antielectrophilic trend observed for the energy gap between the triplet π- and quintet σ-channel (ΔG(T–Q)) stems from the fact that the reaction reactivity can be fine-controlled by the interplay between the exchange-stabilization benefiting from the 5TSH relative to the 3TSH by most nonheme enzymes and the destabilization effect of the orbital by the anionic axial ligand. When the former counteracts the latter, the quintet σ-pathway will be more effective than the other alternatives. Nevertheless, when the dramatic destabilization effect of the orbital by a strong binding axial σ-donor ligand like OH− counteracts but does not override the exchange-stabilization, the barrier in the quintet σ-pathway will remain identical to the triplet π-pathway barrier. Indeed, the axial ligand does not change the intrinsic reaction mechanism in its respective pathway; however, it can affect the energy barriers of different reaction channels for C–H activation. As such, the tuning of the reactivity of the different reaction channels can be realised by increasing/decreasing the electron pushing ability.

The triplet δ-mechanism different from the previously reported ones, i.e., the π-channel with the unoccupied π*xz/yz (FeO) orbital and the σ-channel involving the unoccupied α-spin Fe-σ*z2 orbital, has been theoretically described for the methane hydroxylation by [FeIV = O(TMC)(SR)]+ and its derivative [FeIV = O(TMC)(OH)]+ complex for the first time, and we have undertaken a detailed DFT study on the nature of this state by probing its geometry, electronic property and reactivity in comparison to all other possibilities. DFT calculations indicate that the electron transfer for the 3δ-channel from the σC–H orbital of the substrate to the final acceptor σ*x2−y2 orbital of the catalyst occurs through a complex mechanism, which is initiated by the original α-spin electron transfer from the π* orbital of the catalyst to the σ*x2−y2 orbital, where the α-spin electron from the σC–H orbital of the substrate shifts to the just empty α-spin π* orbital of the catalyst via the O-px/y based π*xz/yz-orbital concomitantly. It is also found that the electron-donating ability of the axial ligand could influence the reaction channels, evident by the distinction that the electron-deficient F− and CF3CO2− ligands react via the 3σ-channel, whereas the electron-rich SR− and OH− ligands proceed by the 3δ-channel. With respect to reactivity, the 3δ-pathway has a comparable barrier to the 3π and 5π-pathways, which may offer a new approach for the specific control of C–H bond activation by the iron(IV)-oxo species.