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2018 Volume 34 Issue 3
2018, 34(3): 227-228
doi: 10.3866/PKU.WHXB201708011
Abstract:
2018, 34(3): 229-230
doi: 10.3866/PKU.WHXB201708282
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2018, 34(3): 231-232
doi: 10.3866/PKU.WHXB201708012
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2018, 34(3): 233-234
doi: 10.3866/PKU.WHXB201708301
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2018, 34(3): 235-236
doi: 10.3866/PKU.WHXB201709041
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2018, 34(3): 237-246
doi: 10.3866/PKU.WHXB201708281
Abstract:
White LEDs are considered the next-generation light source as they are environmentally friendly and have high efficiencies. Therefore, researches are being conducted to meet the performance requirements of phosphors, which are the crucial components of white LEDs. Eu2+ and Eu3+ ions have different electronic structures, which lead to distinct photoluminescence properties. The characteristic emissions of Eu2+ and Eu3+ originate from the 4f-4f and 4f-5d transitions, respectively. In order to combine their respective features, the research of mixed-valence Eu ions into single-phase phosphors has become a hot research topic in recent years. The mixed-valence Eu ion-doped phosphors have tunable luminescence properties because they possess the respective properties of Eu2+ and Eu3+. From their respective characters of Eu2+ and Eu3+, this paper mainly reviews the progress of mixed valence Eu(+2, +3) ion-activated single-component luminescent materials in recent years from three aspects: unbalanced substitution, crystal field regulation, and other systems. In addition, the respective photoluminescence properties of Eu2+ and Eu3+ and the luminescence performances and mechanisms of the mixed-valence Eu ion-activated phosphors have been summarized. The luminescence performances and mechanisms have been summarized as well. All the research works carried out in this field provide inspiration for the investigation of new phosphors.
White LEDs are considered the next-generation light source as they are environmentally friendly and have high efficiencies. Therefore, researches are being conducted to meet the performance requirements of phosphors, which are the crucial components of white LEDs. Eu2+ and Eu3+ ions have different electronic structures, which lead to distinct photoluminescence properties. The characteristic emissions of Eu2+ and Eu3+ originate from the 4f-4f and 4f-5d transitions, respectively. In order to combine their respective features, the research of mixed-valence Eu ions into single-phase phosphors has become a hot research topic in recent years. The mixed-valence Eu ion-doped phosphors have tunable luminescence properties because they possess the respective properties of Eu2+ and Eu3+. From their respective characters of Eu2+ and Eu3+, this paper mainly reviews the progress of mixed valence Eu(+2, +3) ion-activated single-component luminescent materials in recent years from three aspects: unbalanced substitution, crystal field regulation, and other systems. In addition, the respective photoluminescence properties of Eu2+ and Eu3+ and the luminescence performances and mechanisms of the mixed-valence Eu ion-activated phosphors have been summarized. The luminescence performances and mechanisms have been summarized as well. All the research works carried out in this field provide inspiration for the investigation of new phosphors.
2018, 34(3): 247-255
doi: 10.3866/PKU.WHXB201708171
Abstract:
Nitriles are very important for the synthesis of fine chemicals and medicines. However, many nitriles are not widely available, as their synthesis processes pose a serious risk to the environment. Herein, we report that a spontaneous CH3OH/NH3 coupling reaction can directly synthesize N, N-dimethyl cyanamide[(CH3)2NCN], amino acetonitrile [NH2CH2CN], and N, N-dimethyl amino acetonitrile [(CH3)2NCH2CN], when a mixture of methanol and ammonia is transferred into the plasma state via a dielectric barrier discharge. The effects of the plasma reactor configuration, discharge conditions, reaction conditions, and packing materials on the methanol conversion as well as the product selectivity were systematically investigated. Experimental results indicate that, under optimized conditions, a nitrile compound selectivity of 22.1% with a methanol conversion of 51.5% could be achieved. Analysis by optical emission spectroscopy indicates that the C≡N species in CH3OH/NH3 plasma could be a key reactive intermediate aiding in the synthesis of nitrile compounds. The CH3OH/NH3 plasma coupling reaction process is an environment-friendly methodology for the synthesis of (CH3)2NCN, NH2CH2CN, and (CH3)2NCH2CN, and is a potential novel pathway for the synthesis of fine chemicals like methanol and ammonia.
Nitriles are very important for the synthesis of fine chemicals and medicines. However, many nitriles are not widely available, as their synthesis processes pose a serious risk to the environment. Herein, we report that a spontaneous CH3OH/NH3 coupling reaction can directly synthesize N, N-dimethyl cyanamide[(CH3)2NCN], amino acetonitrile [NH2CH2CN], and N, N-dimethyl amino acetonitrile [(CH3)2NCH2CN], when a mixture of methanol and ammonia is transferred into the plasma state via a dielectric barrier discharge. The effects of the plasma reactor configuration, discharge conditions, reaction conditions, and packing materials on the methanol conversion as well as the product selectivity were systematically investigated. Experimental results indicate that, under optimized conditions, a nitrile compound selectivity of 22.1% with a methanol conversion of 51.5% could be achieved. Analysis by optical emission spectroscopy indicates that the C≡N species in CH3OH/NH3 plasma could be a key reactive intermediate aiding in the synthesis of nitrile compounds. The CH3OH/NH3 plasma coupling reaction process is an environment-friendly methodology for the synthesis of (CH3)2NCN, NH2CH2CN, and (CH3)2NCH2CN, and is a potential novel pathway for the synthesis of fine chemicals like methanol and ammonia.
2018, 34(3): 256-262
doi: 10.3866/PKU.WHXB201708071
Abstract:
A new isolated-pentagon-rule (IPR) C100(417)Cl28 has been captured, but its formation mechanism is still unclear. Herein we have used density functional theory (DFT) to study the possible reaction pathways, including Stone-Wales (SW) transformation, direct chlorination, and skeletal transformation for C100(417). The calculated results show that the major source of C100(417) is the skeletal transformation of C102(603), including chloride formation, C2 elimination, and SW transformation. The results satisfactorily explained the experimental observations, and provide useful guidance for the synthesis of fullerene chlorides.
A new isolated-pentagon-rule (IPR) C100(417)Cl28 has been captured, but its formation mechanism is still unclear. Herein we have used density functional theory (DFT) to study the possible reaction pathways, including Stone-Wales (SW) transformation, direct chlorination, and skeletal transformation for C100(417). The calculated results show that the major source of C100(417) is the skeletal transformation of C102(603), including chloride formation, C2 elimination, and SW transformation. The results satisfactorily explained the experimental observations, and provide useful guidance for the synthesis of fullerene chlorides.
2018, 34(3): 270-277
doi: 10.3866/PKU.WHXB201707071
Abstract:
Molecular geometries, electronic structure, and infrared spectroscopy of a series of polyoxometalate (POM)-supported single atom catalyst (SACs) (M1/POM (M = Ni, Pd, Pt, Cu, Ag, Au, POM = [PW12O40]3-) have been studied based on density factional theory (DFT) combined with natural bond orbital (NBO) analysis method. The results show that Pt1/POM has a higher reactivity for activation of N2 relevant to the others. The interaction between the isolated Pt atom and N2 arises from an orbital mixture, which is formed by the dxz and dyz orbital of Pt atom and the π* anti-bond orbit of N2 molecule. The electron transfer from Pt atom to the nitrogen molecule leads to a weakened N≡N bond. The N≡N bond distance increases when compared with the free N2 molecule. All results indicate an effective activation of the nitrogen molecules. For DFT-derived IR spectra, the four characteristic peaks of Keggin-type POM split into five because of introduction of the isolated metal atom.
Molecular geometries, electronic structure, and infrared spectroscopy of a series of polyoxometalate (POM)-supported single atom catalyst (SACs) (M1/POM (M = Ni, Pd, Pt, Cu, Ag, Au, POM = [PW12O40]3-) have been studied based on density factional theory (DFT) combined with natural bond orbital (NBO) analysis method. The results show that Pt1/POM has a higher reactivity for activation of N2 relevant to the others. The interaction between the isolated Pt atom and N2 arises from an orbital mixture, which is formed by the dxz and dyz orbital of Pt atom and the π* anti-bond orbit of N2 molecule. The electron transfer from Pt atom to the nitrogen molecule leads to a weakened N≡N bond. The N≡N bond distance increases when compared with the free N2 molecule. All results indicate an effective activation of the nitrogen molecules. For DFT-derived IR spectra, the four characteristic peaks of Keggin-type POM split into five because of introduction of the isolated metal atom.
2018, 34(3): 286-295
doi: 10.3866/PKU.WHXB201708172
Abstract:
The effect of inserting coordinatively unsaturated metal sites (CUS) into porous aromatic frameworks (PAFs) on their hydrogen storage capacity was investigated systematically by density functional theory and grand canonical Monte Carlo simulations. The results indicate that the maximum excess gravimetric uptake of hydrogen possible with PAF-302MgO2_PBE100 is 7.97% (w) at 77 K. The total uptakes of hydrogen by PAF-302 and PAF-303 functionalized with 100% magnesium alkoxide at 77 K and 10 MPa were determined to be 9.9% (w) (65.9 g∙L-1) and 15.0% (w) (50.5 g∙L-1), respectively. These uptake values are 80% (64.8%) and 173% (26.3%), respectively, more than the gravimetric and volumetric targets set by the Department of Energy (DOE) of USA. They also exceed the targets set by NU-1101, presenting the highest measured performance of 9.9% (w) (46.6 g∙L-1) under the same conditions. Even at 243 K and 10 MPa, the total gravimetric and volumetric uptakes of hydrogen in the former are up to 5.13% (w) and 34.19 g∙L-1, which are about 93.3% and 85.5% of the targets set by DOE, respectively. By analyzing the isosteric heat of adsorption (Qst), radial distribution function, and mass center probability density, it is found that increasing the length of the organic linkers of PAFs incorporated with CUS will result in decreasing volumetric surface areas in spite of the increase in void fractions, which is the root of trade-offs between the total gravimetric and volumetric H2 uptake in porous materials. Additionally, CUS incorporation improves the affinity of PAF materials to H2 molecules, resulting in an enhancement of the volumetric hydrogen storage capacity.
The effect of inserting coordinatively unsaturated metal sites (CUS) into porous aromatic frameworks (PAFs) on their hydrogen storage capacity was investigated systematically by density functional theory and grand canonical Monte Carlo simulations. The results indicate that the maximum excess gravimetric uptake of hydrogen possible with PAF-302MgO2_PBE100 is 7.97% (w) at 77 K. The total uptakes of hydrogen by PAF-302 and PAF-303 functionalized with 100% magnesium alkoxide at 77 K and 10 MPa were determined to be 9.9% (w) (65.9 g∙L-1) and 15.0% (w) (50.5 g∙L-1), respectively. These uptake values are 80% (64.8%) and 173% (26.3%), respectively, more than the gravimetric and volumetric targets set by the Department of Energy (DOE) of USA. They also exceed the targets set by NU-1101, presenting the highest measured performance of 9.9% (w) (46.6 g∙L-1) under the same conditions. Even at 243 K and 10 MPa, the total gravimetric and volumetric uptakes of hydrogen in the former are up to 5.13% (w) and 34.19 g∙L-1, which are about 93.3% and 85.5% of the targets set by DOE, respectively. By analyzing the isosteric heat of adsorption (Qst), radial distribution function, and mass center probability density, it is found that increasing the length of the organic linkers of PAFs incorporated with CUS will result in decreasing volumetric surface areas in spite of the increase in void fractions, which is the root of trade-offs between the total gravimetric and volumetric H2 uptake in porous materials. Additionally, CUS incorporation improves the affinity of PAF materials to H2 molecules, resulting in an enhancement of the volumetric hydrogen storage capacity.
2018, 34(3): 296-302
doi: 10.3866/PKU.WHXB201708241
Abstract:
In this work, a monocrystalline silicon-like material, C40H16Si2, was designed by structural modification based on the tetrahedral bonding features of silicon. The electronic, mechanical, and optical properties of this material were explored by first-principles calculations. The obtained results revealed that this material shows high thermodynamic stability and mechanical stability. The bandgap for Si(C≡C–C6H4–C≡C)4 was calculated to be 3.32 eV, and its valence and conduction bands were located at the Gamma point, indicating that this material is a direct wide-bandgap semiconductor. The Vickers hardness and density of this material were very small, less than one-tenth of that of single-crystalline silicon. The novel compound is a flexible and porous material with low density, and its strong absorption in the UV region makes it a promising semiconductor for blue and green light-emitting diodes.
In this work, a monocrystalline silicon-like material, C40H16Si2, was designed by structural modification based on the tetrahedral bonding features of silicon. The electronic, mechanical, and optical properties of this material were explored by first-principles calculations. The obtained results revealed that this material shows high thermodynamic stability and mechanical stability. The bandgap for Si(C≡C–C6H4–C≡C)4 was calculated to be 3.32 eV, and its valence and conduction bands were located at the Gamma point, indicating that this material is a direct wide-bandgap semiconductor. The Vickers hardness and density of this material were very small, less than one-tenth of that of single-crystalline silicon. The novel compound is a flexible and porous material with low density, and its strong absorption in the UV region makes it a promising semiconductor for blue and green light-emitting diodes.
2018, 34(3): 314-322
doi: 10.3866/PKU.WHXB201709042
Abstract:
Following the exceptional success of density functional theory (DFT) in the realm of quantum chemistry, the conceptual DFT (CDFT) method has been widely used for describing the dynamic reactivity index of reactive chemicals in recent years. Reactive chemicals refer to those that bind covalently to biological macromolecules; in other words, the binding of the ligand with the receptor or enzyme involved with the breakage of the old bond and the process of formation of the new bond. Organophosphorus AChE irreversible inhibitors are reactive chemicals. In the present work, we calculated the reactivity descriptors for AChE irreversible inhibitors (organophosphate compounds), including some pesticides and chemical warfare agents, by the CDFT method at the B3LYP/6-311++G(2d, 3p)/gas, B3LYP/6-311++G(2d, 3p)/CPCM/water, MP2/6-311++G(2d, 3p)/gas, MP2/6-311++G(2d, 3p)/CPCM/water levels, in order to analyze their reactivity and determine the optimal parameters for calculation. Reactivity descriptors such as chemical potential (μ), vertical ionization energy (I), vertical electronic affinity (A), molecular absolute hardness (η), electrophilicity (ω), condensed atomic Fukui function, and varied natural bond orbital (NBO) bond order, were used to identify changes in the reactivity of these compounds in the gas and aqueous phases with the conductor-like polarizable continuum model (CPCM) model. The values of the reactivity descriptors and quantitative structure-property relationship (QSPR) models indicated that: the center of the phosphor atom (P) was the nucleophilic reaction site with AChE for most of selected compounds; substituted tertiaryamine protonization in organophosphorus compounds greatly enhanced the electrophilic attackingability of the P reaction center; and as a whole, conformation did not have a significant effect on the reactivity for theDFT/B3LYP method, with an exception for the MP2 method which showed a comparative instability in results. The initial QSPR model in training sets of pLD50 with stepwise regression analysis shows that the B3LYP/6-311++G(2d, 3p)/gas level can provide a better result than the MP2 level and in the water phase, and provides a good representation of the molecular structure-toxicity relationship. These predictions for the compounds surpass those obtained by conventional QSPR equations, which do not consider electron transfer in the phosphorylated or aged process, thereby providing unreliable predictions. The proposed reactivity concept using the CDFT principle possesses a definite physical meaning, reflects the dynamic reactivity from the ground state of the molecular structure, and can be applied to toxicity predictions for AChE irreversible inhibitors with greater precision and stability.
Following the exceptional success of density functional theory (DFT) in the realm of quantum chemistry, the conceptual DFT (CDFT) method has been widely used for describing the dynamic reactivity index of reactive chemicals in recent years. Reactive chemicals refer to those that bind covalently to biological macromolecules; in other words, the binding of the ligand with the receptor or enzyme involved with the breakage of the old bond and the process of formation of the new bond. Organophosphorus AChE irreversible inhibitors are reactive chemicals. In the present work, we calculated the reactivity descriptors for AChE irreversible inhibitors (organophosphate compounds), including some pesticides and chemical warfare agents, by the CDFT method at the B3LYP/6-311++G(2d, 3p)/gas, B3LYP/6-311++G(2d, 3p)/CPCM/water, MP2/6-311++G(2d, 3p)/gas, MP2/6-311++G(2d, 3p)/CPCM/water levels, in order to analyze their reactivity and determine the optimal parameters for calculation. Reactivity descriptors such as chemical potential (μ), vertical ionization energy (I), vertical electronic affinity (A), molecular absolute hardness (η), electrophilicity (ω), condensed atomic Fukui function, and varied natural bond orbital (NBO) bond order, were used to identify changes in the reactivity of these compounds in the gas and aqueous phases with the conductor-like polarizable continuum model (CPCM) model. The values of the reactivity descriptors and quantitative structure-property relationship (QSPR) models indicated that: the center of the phosphor atom (P) was the nucleophilic reaction site with AChE for most of selected compounds; substituted tertiaryamine protonization in organophosphorus compounds greatly enhanced the electrophilic attackingability of the P reaction center; and as a whole, conformation did not have a significant effect on the reactivity for theDFT/B3LYP method, with an exception for the MP2 method which showed a comparative instability in results. The initial QSPR model in training sets of pLD50 with stepwise regression analysis shows that the B3LYP/6-311++G(2d, 3p)/gas level can provide a better result than the MP2 level and in the water phase, and provides a good representation of the molecular structure-toxicity relationship. These predictions for the compounds surpass those obtained by conventional QSPR equations, which do not consider electron transfer in the phosphorylated or aged process, thereby providing unreliable predictions. The proposed reactivity concept using the CDFT principle possesses a definite physical meaning, reflects the dynamic reactivity from the ground state of the molecular structure, and can be applied to toxicity predictions for AChE irreversible inhibitors with greater precision and stability.
2018, 34(3): 263-269
doi: 10.3866/PKU.WHXB201708173
Abstract:
In this work, the Fukui functions of the two 2P resonance states of Be-, a 2P resonance state of Mg-, and a 2D resonance state of Ca- have been determined. The trajectories of these resonance states, in conjunction with the complex rotation of the Hamiltonian, were used to determine their wave functions. The electron densities, Fukui functions, and values of the hyper-radius < r2 > were computed from these wave functions. The Fukui functions have negative regions in the valence shell in addition to the inner shell regions, indicating screening effects of the outer temporary electron. Selected configuration interactions with up to quadruple excitations were used along the trajectories and for computing the final wave function. Based on this data, the densities, Fukui functions, and < r2 > were calculated.
In this work, the Fukui functions of the two 2P resonance states of Be-, a 2P resonance state of Mg-, and a 2D resonance state of Ca- have been determined. The trajectories of these resonance states, in conjunction with the complex rotation of the Hamiltonian, were used to determine their wave functions. The electron densities, Fukui functions, and values of the hyper-radius < r2 > were computed from these wave functions. The Fukui functions have negative regions in the valence shell in addition to the inner shell regions, indicating screening effects of the outer temporary electron. Selected configuration interactions with up to quadruple excitations were used along the trajectories and for computing the final wave function. Based on this data, the densities, Fukui functions, and < r2 > were calculated.
2018, 34(3): 278-285
doi: 10.3866/PKU.WHXB201708174
Abstract:
The concept of resonance-assisted hydrogen bonds (RAHBs) highlights the synergistic interplay between the π-resonance and hydrogen bonding interactions. This concept has been well-accepted in academia and is widely used in practice. However, it has been argued that the seemingly enhanced intramolecular hydrogen bonding (IMHB) in unsaturated compounds may simply be a result of the constraints imposed by the σ-skeleton framework. Thus, it is crucial to estimate the strength of IMHBs. In this work, we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone. One approach is the block-localized wavefunction (BLW) method, which is a variant of the ab initio valence bond (VB) theory. Using this approach, it is possible to derive the geometries and energetics with resonance shut down. The other approach is Edmiston's truncated localized molecular orbital (TLMO) technique, which monitors the energy changes by removing the delocalization tails from localized molecular orbitals. The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced by π-resonance, and that this enhancement is not a result of σ constraints.
The concept of resonance-assisted hydrogen bonds (RAHBs) highlights the synergistic interplay between the π-resonance and hydrogen bonding interactions. This concept has been well-accepted in academia and is widely used in practice. However, it has been argued that the seemingly enhanced intramolecular hydrogen bonding (IMHB) in unsaturated compounds may simply be a result of the constraints imposed by the σ-skeleton framework. Thus, it is crucial to estimate the strength of IMHBs. In this work, we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone. One approach is the block-localized wavefunction (BLW) method, which is a variant of the ab initio valence bond (VB) theory. Using this approach, it is possible to derive the geometries and energetics with resonance shut down. The other approach is Edmiston's truncated localized molecular orbital (TLMO) technique, which monitors the energy changes by removing the delocalization tails from localized molecular orbitals. The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced by π-resonance, and that this enhancement is not a result of σ constraints.
2018, 34(3): 303-313
doi: 10.3866/PKU.WHXB201708302
Abstract:
A unified explanation for the relative stability of linear and branched alkanes is still lacking, and research in this direction is ongoing. Unlike the conventional orbital-based description, we have employed the density functional theory (DFT) based on the total energy and its components as well as a newly proposed energy partitioning scheme [Liu, S. B. J. Chem. Phys. 2007, 126, 244103]. Taking monosubstituted hydrocarbons CnH2n+1―R (n = 3, 4, 5, 6; R = OH, OCH3, NH2, NO2, F, Cl, CN, CHO) as examples, we have investigated the molecular origin and nature within the framework of the DFT. Our computational results revealed that no such a single energy component that dictates the transformation of the mono-substituted alkane derivatives. By the binary fit of the electrostatic potential and steric hindrance from the new energy decomposition scheme, we unraveled that isomerization is mainly governed by the electrostatic potential, while the steric effect has a minor influence. Moreover, we established a linear relationship between the Shannon entropy difference and the Fisher information difference, which is accordance with previous findings. Further, there was no linear relationship between Ee and the Fisher information or Shannon entropy.
A unified explanation for the relative stability of linear and branched alkanes is still lacking, and research in this direction is ongoing. Unlike the conventional orbital-based description, we have employed the density functional theory (DFT) based on the total energy and its components as well as a newly proposed energy partitioning scheme [Liu, S. B. J. Chem. Phys. 2007, 126, 244103]. Taking monosubstituted hydrocarbons CnH2n+1―R (n = 3, 4, 5, 6; R = OH, OCH3, NH2, NO2, F, Cl, CN, CHO) as examples, we have investigated the molecular origin and nature within the framework of the DFT. Our computational results revealed that no such a single energy component that dictates the transformation of the mono-substituted alkane derivatives. By the binary fit of the electrostatic potential and steric hindrance from the new energy decomposition scheme, we unraveled that isomerization is mainly governed by the electrostatic potential, while the steric effect has a minor influence. Moreover, we established a linear relationship between the Shannon entropy difference and the Fisher information difference, which is accordance with previous findings. Further, there was no linear relationship between Ee and the Fisher information or Shannon entropy.
