NBO Charge Analysis Research Articles

Cyclic Carbonate Formation from Epoxides and CO2 Catalyzed by Sustainable Alkali Halide-Glycol Complexes: A DFT Study to Elucidate Reaction Mechanism and Catalytic Activity.

We provide a comprehensive DFT investigation of the mechanistic details of CO2 fixation into styrene oxide to form styrene carbonate, catalyzed by potassium iodide–tetraethylene glycol complex. A detailed view on the intermediate steps of the overall reaction clarifies the role of hydroxyl substances as co-catalysts for the alkali halide-catalyzed cycloaddition. The increase of iodide nucleophilicity in presence of tetraethylene glycol is examined and rationalized by NBO and Hirshfeld charge analysis, and bond distances. We explore how different alkali metal salts and glycols affect the catalytic performance. Our results provide important hints on the synthesis of cyclic carbonates from CO2 and epoxides promoted by alkali halides and glycol complexes, allowing the development of more efficient catalysts.

Silver-graphene quantum dots based electrochemical sensor for trinitrotoluene and p-nitrophenol

Abstract Silver cluster decorated graphene quantum dots act as efficient electrochemical sensors for the detection of nitroaromatic compounds due to their unique electronic properties. Herein, we report the first detailed theoretical study about the sensing ability of silver-graphene composites for the electrochemical detection of trinitrotoluene (TNT) & p-nitrophenol (p-NP). The complexes of TNT and p-NP with silver-graphene composite are quite stable as evident from their higher interaction energies (−15.64 to −70.07 kcal mol−1). The NBO charge analysis, DOS analysis, frontier molecular orbital analysis, UV–visible analysis, non-covalent interactions (NCI) & charge decomposition analysis (CDA) supported the interaction mechanism in TNT@Ag6-coronene & p-NP@Ag6-coronene complexes. NBO charge analysis results reveal that the charge is transferred from substrates to analytes except in p-NP@coronene and p-NP@coronene-Ag6 complexes. The generation of new energy states in DOS spectra reflect the chemical sensitivity of the system. Frontier molecular orbital analysis results validate a substantial decrease in the H-Lgap of silver-coronene composite on interaction with analytes. The shifting (red & blue) of λmax during interactions of analytes with silver-coronene is affirmed from excited state analysis. The NCI plots show that some steric repulsion is also there along with strong non-covalent electrostatic (M…O) & unusual van der Waals (M…H) interactions. The evaluated results of CDA validate the charge transfer interactions between various fragment pairs of complexes. The precedent results distinctly show the better sensing performance of silver-graphene composites towards TNT & p-NP.

Volatile organic compounds sensing by Li/Ti doped ethylene complex

First principles calculations and atom centered density matrix propagation (ADMP) molecular dynamics (MD) simulations are performed to study the adsorption of small volatile organic compounds (VOCs) like HCHO, CH4, CHF3 and CH3OH on Li/Ti metal doped ethylene complex (C2H4M, M = Li, Ti). The sensitivity of C2H4M complex upon VOCs adsorption is examined through change in structural parameters and electronic properties of a complex. The NBO charge analysis is carried out to measure charge transfer during adsorption process. The interaction between VOCs and C2H4M complex is analysed in detail with the help of PDOS plot and frontier molecular orbital analysis. Effect of VOCs adsorption on binding energy of Li/Ti metal atom to C2H4 substrate in C2H4M complex is also studied. The operating temperature and pressure of sensor is determined by calculating temperature and pressure dependent Gibbs free energy corrected adsorption energies and confirmed through ADMP–MD simulations. Quantum mechanical stability of VOCs adsorbed complexes is confirmed by vibrational frequency analysis. This study suggests potential application of C2H4M complex as a VOC gas sensing material for HCHO, CH4, CHF3 and CH3OH compounds.

Donor→acceptor coordination interactions in 1,3-bis(NHC)triazenyl Cations: An electronic structure analysis.

Donor→acceptor coordination interactions (L → N) between ligands and nitrogen center as in L → N⊕ ← L were reported in the recent past. This article describes the possibility of L → N coordination interactions in triazenyl cation species L → N3 ⊕ ← L. A few 1,3-bis(NHC)triazenyl cation species were experimentally known, the electronic structure analysis reported in this work reveals the presence of L → N (donor→acceptor) interactions in these species. Molecular orbital analysis, NBO charge analysis, energy decomposition analysis, and so forth, confirm the possibility of L → N coordination bond character. Ten molecules with the general formula L → N3 ⊕ ← L have been designed carrying L → N3 ⊕ ← L interactions. © 2019 Wiley Periodicals, Inc.

A theoretical study on the mechanism and kinetics of toxic PCDD destruction by OH radicals

The mechanism and kinetics of toxic PCDDs destruction by OH radicals is investigated in detail by employing quantum chemistry. Results show that the OH radical degrades toxic PCDDs via substituting chlorine at the 2, 3, 7, 8 positions. The kinetic parameters are calculated by adopting transition state theory. The rate constant of OCDD destruction by OH is in agreement with the experimental result, especially at 298 K. The rate constants of 2, 3, 7, 8-TCDD destruction are obviously lower than those of other toxic PCDDs. The reason is discussed by using the NBO charge analysis. Owing to the activation effect of Cl atoms at 1, 4, 6, 9 positions, C atoms at 2, 3, 7, 8 positions have more negative charge. At aromatic rings, if the carbon has more negative charge, the carbon is more easily attacked by OH and the adjacent Cl is more easily substituted.

Organolithium complex as a gas sensing material for oxides from ab initio calculations and molecular dynamics simulations

AbstractGas sensing study of C2H4Li complex toward oxides viz. CO, CO2, NO, NO2, SO, and SO2 gas molecules has been carried out using ab initio method. Different possible configurations of gas molecule adsorption on C2H4Li complex are considered. The structural parameters of most stable configuration of gas molecule adsorbed complexes are thoroughly analysed. Electronic properties are studied using total density of states (DOS) plot. Charge transferred between the gas molecule and the substrate is studied using NBO charge analysis. Gas sensing of all the six gas molecules is possible at ambient conditions. Atom centred density matrix propagation (ADMP) molecular dynamics simulations confirmed that all the gas molecules remain adsorbed on C2H4Li complex at room temperature during the simulation. This study suggests that the C2H4Li complex acts as a novel gas sensing material for CO, CO2, NO, NO2, SO, and SO2 gas molecules at ambient conditions, below room temperature as well as at high pressure.

Crystal structure, spectroscopic, electronic, luminescent and nonlinear optical properties of (S)-4-Amino-5-(1-hydroxy-ethyl)-2,4-dihydro-[1,2,4]triazole-3-thione: A combined experimental and DFT study

4-Amino-5-(1-hydroxy-ethyl)-2,4-dihydro-[1,2,4]triazole-3-thione was synthesized and characterized by single crystal x-ray analysis. Thermodynamic calculations at B3LYP/6-31+G(d,p) level of theory proved that 4-Amino-5-(1-hydroxy-ethyl)-2,4-dihydro-[1,2,4]triazole-3-thione is the most stable tautomer in comparison with (S)-1-(4-Amino-5-mercapto-4H-[1,2,4]triazol-3-yl)-ethanol and (S)-4-Amino-5-(1-hydroxy-ethyl)-4,5-dihydro-[1,2,4] triazole-3-thione respectively. The title compound has been analyzed for its photophysical properties through vibration, absorption and photoluminescence spectroscopy. Theoretical calculations of the title compound were performed at B3LYP/6-31+G(d,p) level of theory in order to gain insight into the geometric, electronic and non-linear optical properties. Theoretical 1H and 13C NMR spectra calculated through GIAO formalism at B3LYP/6-311+G(2d,p) level in DMSO solvent showed excellent correlation with the experimental spectra. The experimental solid state photoluminescence spectrum was studied for the title compound. NBO charge analysis has also been performed to study charge transfer. Nonlinear optical properties analysis of the title compound reveals that the first static hyperpolarizability of 4-Amino-5-(1-hydroxy-ethyl)-2,4-dihydro-[1,2,4]triazole-3-thione is 9 times higher than urea (a commercial NLO material).

Boron/nitrogen substituted the staggered hetero-dimers: Fascinating intermolecular charge-transfer and large NLO responses

Recently, the structure-property relationships of an attractive isomeric radical 1 (Phys. Chem. Chem. Phys., 2016, 18, 29041–29044) with famous phenalenyl (PLY) was investigated. Can PLY and 1 form stable π-dimers? The single point energy scan result shows that the staggered π-dimer (2) has the lowest energy. In order to explore intermolecular charge-transfer and nonlinear optical property, two π-dimers (2a and 2b by boron and nitrogen atoms substituting the central carbon atoms of 2) are designed. 2 has smaller intermolecular charge-transfer (0.020) and the first hyperpolarizability (βtot, 3.18 × 102 au). However, boron and nitrogen substitution effect can greatly enhance intermolecular charge-transfer (0.215 for 2a and 0.181 for 2b) and the βtot values (6.32 × 103 for 2a and 6.80 × 103 for 2b). Interestingly, the βtot values of 2a and 2b are close to each other, but their βz components and the NBO charge analysis show that 2a and 2b have opposite direction of charge transfer, which can be well explained by the difference of the dipole moment component (Δμz) between the ground and the excited states. Further, the first hyperpolarizability density study clearly substantiates the difference in their βzzz values: negative contribution for 2a is much larger than positive contribution, while the first hyperpolarizability density for 2b shows much larger positive contribution. Thus, the primary component of βzzz is negative value for 2a and βzzz is positive value for 2b. Combining with the frontier molecular orbital (FMO) and the electron density difference map (EDDM), intermolecular charge-transfer transition from B substituted fragment to N substituted fragment for 2a and 2b is concluded. The significant structure-property relationships in present π-dimers are beneficial for further theoretical and experimental investigations of high-performance nonlinear optical materials.

Insight into the excited-state intramolecular double-proton transfer of the 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol: one-step or stepwise mechanism?

The excited-state double-proton transfer mechanism of 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol has been theoretically investigated based on the methods of density functional theory and time-dependent density functional theory. Geometric structure comparison and infrared vibrational spectra analysis confirm that the strengthening of the intramolecular hydrogen bond in the first excited state (S1) has facilitated the proton transfer process. The frontier molecular orbitals analysis illustrates that the nature of the hydrogen bond enhancement lies in the charge redistribution upon photo-excitation, which is further confirmed by NBO charge analysis quantitatively. The reduced dimensionality (two-dimensional) potential energy surfaces have been scanned for both the ground state (S0) and the first electronic excited state to reveal the mechanism and pathway of the two protons being transferred. Compared with the concerted path of proton transfer, the stepwise path with one proton being transferred first and then a second one followed exhibits a relatively mild energy barrier and seems to be more rational and favorable.

Molecular structures, charge distributions, and vibrational analyses of the tetracoordinate Cu(II), Zn(II), Cd(II), and Hg(II) bromide complexes of p-toluidine investigated by density functional theory in comparison with experiments

The Cu(II), Zn(II), Cd(II), and Hg(II) bromide complexes of p-toluidine have been studied with B3LYP calculations by using def2-TZVP basis set at the metal atoms and using def2-TZVP and 6-311G+(d,p) basis sets at the remaining atoms. Both basis set combinations give analogous results, which validate the use of quickly converging 6-311G+(d,p) basis set in future studies. The molecular structures, atomic charge and spin distributions, and harmonic vibrational frequencies of the complexes have been calculated. The Zn, Cd and Hg complexes have been found to have distorted tetrahedral environments around the metal atoms whereas Cu complex has a square planar geometry. The NBO charge analysis have been found more accurate and less misleading compared with the Mulliken scheme. The present vibrational spectra calculations allow accurate assignment of the vibrational bands, which otherwise assigned tentatively in previous experimental-only studies.

Application of carbon nanostructures toward SO2 and SO3 adsorption: a comparison between pristine graphene and N-doped graphene by DFT calculations

We studied the adsorption of SOx (x = 2,3) molecules on the surface of pristine graphene (PG) and N-doped graphene (NDG) by density functional theory (DFT) calculations at the B3LYP/6-31G(d) level. We used Mulliken and NBO charge analysis to calculate the net charge transfer of adsorbed SOx on pristine and defected graphene systems. Our calculations reveal much higher adsorption energy and higher net charge transfer by using NDG instead of pristine graphene. Furthermore, the density of state (DOS) graphs point to major orbital hybridization between the SOx and NDG, while there is no evidence of hybridization by using pristine graphene. Based on our results, it is found that SO2 and SO3 molecules can be adsorbed on the surface of NDG physically and chemically with adsorption energies (Eads) of −27.5 and 65.2 kJ mol−1 (19.6 and 51.4 kJ mol−1 BSSE), respectively, while low adsorption energies were calculated in the case of using pristine graphene. So we introduced NDG as a sensitive adsorbent/sensor for detection of SO2 and SO3.

Noble-Gas-Inserted Fluoro(sulphido)boron (FNgBS, Ng = Ar, Kr, and Xe): A Theoretical Prediction.

The possibility of the existence of a new series of neutral noble gas compound, FNgBS (where Ng = Ar, Kr, Xe), is explored theoretically through the insertion of a Ng atom into the fluoroborosulfide molecule (FBS). Second-order Møller-Plesset perturbation theory, density functional theory, and coupled cluster theory based methods have been employed to predict the structure, stability, harmonic vibrational frequencies, and charge distribution of FNgBS molecules. Through energetics study, it has been found that the molecules could dissociate into global minima products (Ng + FBS) on the respective singlet potential energy surface via a unimolecular dissociation channel; however, the sufficiently large activation energy barriers provide enough kinetic stability to the predicted molecules, which, in turn, prevent them from dissociating into the global minima products. Moreover, the FNgBS species are thermodynamically stable, owing to very high positive energies with respect to other two two-body dissociation channels, leading to FNg + BS and F(-) + NgBS(+), and two three-body dissociation channels, corresponding to the dissociation into F + Ng + BS and F(-) + Ng + BS(+). Furthermore, the Mulliken and NBO charge analysis together with the AIM results reveal that the Ng-B bond is more of covalent in nature, whereas the F-Ng bond is predominantly ionic in character. Thus, these compounds can be better represented as F(-)[NgBS](+). This fact is also supported by the detail analysis of bond length, bond dissociation energy, and stretching force constant values. All of the calculated results reported in this work clearly indicate that it might be possible to prepare and characterize the FNgBS molecules in cryogenic environment through matrix isolation technique by using a mixture of OCS/BF3 in the presence of large quantity of noble gas under suitable experimental conditions.

Spectral investigations, DFT computations and molecular docking studies of the antimicrobial 5-nitroisatin dimer

5-Nitroisatin is used for the treatment of fungal and bacterial strains exploring antimicrobial activity. Structural and vibrational spectroscopic studies were carried out by using FT-IR, FT Raman, UV and NMR spectral analysis together with DFT method using Gaussian’09 software. Assignments of vibrational spectra have been carried out with the aid of NCA. NBO analysis, Charge Analysis, HOMO LUMO, ESP, aromaticity and thermodynamic properties have been analyzed. Thermal stability has been analyzed by TG/DTA method. 5NI has been screened for its antimicrobial activity and found to exhibit antifungal and antibacterial effects. Docking simulation has been performed.

Theoretical insights into the reaction mechanism and solvation effect of conjugate addition of dimethyl propanedioate to 1-nitroprop-1-ene catalyzed by cinchona alkaloids

The conjugate addition reaction of dimethyl propanedioate to 1-nitroprop-1-ene catalyzed by cinchona alkaloid derivatives (QD-R″) is investigated using density functional theory calculations in this paper. The geometry optimizations and frequency calculations were carried out at the B3LYP/6-31G(d,p) level, and the accurate energetic parameters were obtained by the B3LYP/6-311++G(2df,2p) method. Our calculations find that cinchona alkaloids with –NCONHPh and –NH electron-withdrawing substituents in the quinuclidine show stronger activation on the system than that with –CH2 electron-donating substituent. The NBO charge analysis for the tertiary amine nitrogen of the quinuclidine affirms that the electron-withdrawing substituents decrease the negative charges on the tertiary amine nitrogen atom, which is favorable for the second proton transfer from the catalyst to α-carbon of 1-nitroprop-1-ene. As a result, the calculations show that the charge distribution of the tertiary amine nitrogen affects the catalytic efficiency of the system. Furthermore, a detailed analysis of the effects of the solvent on the system further revealed the regularity.

Mechanistic DFT Study on Ethylene Trimerization of Chromium Catalysts Supported by a Versatile Pyrrole Ligand System

To elucidate fundamental mechanistic aspects of the landmark Chevron–Phillips ethylene trimerization system, a detailed theoretical study has been carried out by DFT methods on an aluminum pyrrolyl chromium catalyst. Reaction pathways for selective ethylene oligomerization have been successfully located on the basis of the metallacycle mechanism. Consistent with experimental results, for the model system ethylene trimerization was proven to be energetically preferred in comparison to ethylene dimerization or further ring expansion toward the formation of higher α-olefins. The Cr(I/III) redox couple was found to be the most likely for the catalytic ethylene trimerization. A careful electronic configuration analysis has been conducted, and the ground state of all active species involved in the catalytic cycle is identified to be S = 3/2 except for the bare active species, which favors a high spin state of S = 5/2. The role of a pendant chlorine functionality has been investigated as well. Variable Cr–Cl bond distance and NBO charge analysis of every intermediate clearly exhibit the hemilabile behavior of the chlorine. This unique hemilability is considered to be a key factor for the selectivity toward 1-hexene formation.

Reducing polyaromatic hydrocarbons: the capability and capacity of lithium

Materials which are extensively and effectively reduced by lithium atoms are of outstanding importance in the lithium battery industry and carbonaceous materials show great promise in this area. Benzene (B), naphthalene (N), anthracene (A) and tetracene (T) are considered as prototypical carbonaceous materials, which mimic sp2 allotropical forms of carbon such as graphene, graphite, carbon nanotubes (CNT) and fullerenes. We have studied lithium adsorption in these carbonaceous materials and analyzed the reduction capability of lithium by different approaches. We observed that the binding energy of these polycyclic aromatic hydrocarbon (PAH)–lithium complexes highly depends on the positioning of the lithium atoms and the size of the PAH. The sequential binding energy data show that the adsorption of the second Li atom is more facile in nature as indicated by its higher binding strengths. The NBO charge analysis also reflects that neutral lithium acquires fractional positive charges which vary from 0.4 a.u. to 2.81 a.u upon interaction with the PAH, which is a clear indication of the ability of the lithium atoms to reduce the PAH molecules. A good correlation has been obtained between the extent of charge transfer, binding and deformation energies. The current study provides the first systematic and exhaustive analysis of the sequential addition of Li atoms to carbonaceous materials and computationally estimates the reduction abilities of this class of materials.

DFT Study of Polyaniline NH3, CO2, and CO Gas Sensors: Comparison with Recent Experimental Data

Density functional theory studies (DFT) have been carried out to evaluate the ability of polyaniline emeraldine salt (PANI ES) from 2 to 8 phenyl rings as sensor for NH3, CO2, and CO. The sensitivity and selectivity of nPANI ES among NH3, CO2, and CO are studied at UB3LYP/6-31G(d) level of theory. Interaction of nPANI ES with CO is studied from both O (CO(1)) and C (CO(2)) sides of CO. Interaction energy, NBO, and Mulliken charge analysis were used to evaluate the sensing ability of PANI ES for different analytes. Interaction energies are calculated and corrected for BSSE. Large forces of attraction in nPANI ES-NH3 complexes are observed compared to nPANI ES–CO2, nPANI ES-CO(1), and nPANI ES-CO(2) complexes. The inertness of +C≡O– in nPANI ES-CO(1) and nPANI ES-CO(2) complexes are also discussed. Frontier molecular orbitals and energies indicate that NH3 changes the orbital energy of nPANI ES to a greater extent compared to CO2, CO(1), and CO(2). Peaks in UV–vis and UV–vis–near-IR spectra of nPANI ES are ...

The structures of neutral transition metal doped silicon clusters, Sin X (n = 6−9; X = V, Mn)

We present a combined experimental and theoretical investigation of small neutral vanadium and manganese doped silicon clusters Si(n)X (n = 6-9, X = V, Mn). These species are studied by infrared multiple photon dissociation and mass spectrometry. Structural identification is achieved by comparison of the experimental data with computed infrared spectra of low-lying isomers using density functional theory at the B3P86∕6-311+G(d) level. The assigned structures of the neutral vanadium and manganese doped silicon clusters are compared with their cationic counterparts. In general, the neutral and cationic Si(n)V(0,+) and Si(n)Mn(0,+) clusters have similar structures, although the position of the capping atoms depends for certain sizes on the charge state. The influence of the charge state on the electronic properties of the clusters is also investigated by analysis of the density of states, the shapes of the molecular orbitals, and NBO charge analysis of the dopant atom.

Mechanism of Silver(I)‐Catalyzed Enantioselective Synthesis of Axially Chiral Allenes Based on Propargylamines

AbstractThe silver(I)‐catalyzed synthesis picture of axially chiral allenes based on propargylamines has been outlined using density functional theory (DFT) method for the first time. Our calculations find that, the coordination of silver(I) into triple bond of propargylamines at anti‐position of nitrogen shows a stronger activation on the triple bond than that at cis‐position, which is favorable for the subsequent hydrogen transfer. The NBO charge analysis for the hydrogen transfer affirms the experimental speculation that this step is a hydride transfer process. The energy barrier of the anti‐periplanar elimination of vinyl‐silver is 26.9 kJ·mol−1 lower than that of the syn‐periplanar elimination, supporting that (−)‐allene is the main product of this reaction. In a word, the most possible route for this reaction is that the silver(I) coordinates into the triple bond of propargylamines at anti‐position of nitrogen, then the formed silver(I) complex undergoes a hydride transfer to give a vinyl‐silver, finally the vinyl‐silver goes through an anti‐periplanar elimination to give (−)‐allene. The hydride transfer with the energy barrier of 44.8 kJ·mol−1 is the rate‐limiting step in whole catalytic process. This work provides insight into why this reaction has a very high enantioselectivity.

Selective fluorescent probes based on C [dbnd]N isomerization and intramolecular charge transfer (ICT) for zinc ions in aqueous solution

As the second most abundant transition-metal ion in the human body, Zn 2+ plays crucial roles in many important biological processes; while in the environment, an excessive concentration of Zn 2+ may reduce the soil microbial activity resulting in phytotoxic effects. Therefore, developing effective and sensitive detection method for Zn 2+ has become crucially important and necessary both in life and environment science. Two new fluorescence probes, 2-((2-hydroxynaphthalen-1-yl)methyleneamino)-3-(1H-imidazol-5-yl) propanoic acid ( 2) and 2-hydroxy-2-((2-hydroxynaphthalen-1-yl) methyleneamino) acetic acid ( 3), were easily prepared by a one step reaction between 2-hydroxy-1-naphthaldehyde with histidine and serine, respectively, in ethanol. The optical properties of them were investigated by fluorescence spectra, which displayed specific and sensitive recognition to Zn 2+ and especially avoided the interference of Cd 2+ when they were tested against a range of physiological and environmentally relevant metal ions in aqueous solution. The responsive mechanism of the two probes to Zn 2+ were involved both the C N isomerization and ICT, which were clarified by NBO charge analysis and the HOMO–LUMO energy gap calculation by using B3LYP/6-31G density functional theory.