scholarly journals Unsaturated and Benzannulated N-Heterocyclic Carbene Complexes of Titanium and Hafnium: Impact on Catalysts Structure and Performance in Copolymerization of Cyclohexene Oxide with CO2

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4364
Author(s):  
Lakshmi Suresh ◽  
Ralte Lalrempuia ◽  
Jonas B. Ekeli ◽  
Francis Gillis-D’Hamers ◽  
Karl W. Törnroos ◽  
...  
Keyword(s):  
Density Functional ◽  
Lone Pair ◽  
Catalytic Performance ◽  
Nbo Analysis ◽  
Cyclohexene Oxide ◽  
Group 4 ◽  
Low Co2 ◽  
And Performance ◽  
High Yields ◽  
Oxygen Lone Pair

Tridentate, bis-phenolate N-heterocyclic carbenes (NHCs) are among the ligands giving the most selective and active group 4-based catalysts for the copolymerization of cyclohexene oxide (CHO) with CO2. In particular, ligands based on imidazolidin-2-ylidene (saturated NHC) moieties have given catalysts which exclusively form polycarbonate in moderate-to-high yields even under low CO2 pressure and at low copolymerization temperatures. Here, to evaluate the influence of the NHC moiety on the molecular structure of the catalyst and its performance in copolymerization, we extend this chemistry by synthesizing and characterizing titanium complexes bearing tridentate bis-phenolate imidazol-2-ylidene (unsaturated NHC) and benzimidazol-2-ylidene (benzannulated NHC) ligands. The electronic properties of the ligands and the nature of their bonds to titanium are studied using density functional theory (DFT) and natural bond orbital (NBO) analysis. The metal–NHC bond distances and bond strengths are governed by ligand-to-metal σ- and π-donation, whereas back-donation directly from the metal to the NHC ligand seems to be less important. The NHC π-acceptor orbitals are still involved in bonding, as they interact with THF and isopropoxide oxygen lone-pair donor orbitals. The new complexes are, when combined with [PPN]Cl co-catalyst, selective in polycarbonate formation. The highest activity, albeit lower than that of the previously reported Ti catalysts based on saturated NHC, was obtained with the benzannulated NHC-Ti catalyst. Attempts to synthesize unsaturated and benzannulated NHC analogues based on Hf invariably led, as in earlier work with Zr, to a mixture of products that include zwitterionic and homoleptic complexes. However, the benzannulated NHC-Hf complexes were obtained as the major products, allowing for isolation. Although these complexes selectively form polycarbonate, their catalytic performance is inferior to that of analogues based on saturated NHC.

Density Functional Theory (DFT) and Natural Bond Orbital (NBO) Investigation of Intra/Intermolecular Hydrogen Bond Interaction in Sulfonated Nata-De Coco-Water (NDCS-(H2O)n)

2020 ◽  
Vol 17 (6) ◽  
pp. 2812-2819
Author(s):  
Sitti Rahmawati ◽  
Cynthia Linaya Radiman ◽  
Muhamad Abdulkadir Martoprawiro ◽  
Siti Nuryanti
Keyword(s):  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Density Functional ◽  
Intermolecular Hydrogen Bond ◽  
Lone Pair ◽  
Dft Method ◽  
Nbo Analysis ◽  
Hydrogen Bond Interaction ◽  
Sulfonic Group ◽  
The One

This research aim to study the conformation, hydrogen bonding network, and stability of all possible molecular interactions between sulfonated nata-de-coco membranes with water (NDCS-(H2O)n), n = 1–5) as well as associate them with results of phosphorylated nata-de-coco reported previously, to determine the potential of proton transfer within both systems. The calculations used DFT method at the B3LYP/6-311G** level as well as NBO analysis. The strongest hydrogen bonds were found among sulfonic group in NDCS-(H2O)5 and the oxygen in the water molecules. The stabilization energy of NDCS-(H2O)5 is 98.9 kcal/mol, That is much greater than that found in NDCP-(H2O)5 This suggests that the NDCS was more easily to donate its lone pair and that the hydrogen bonds between sulfonic group and water molecule were stronger, so that it was easier to transfer protons to another sulfonic group than to NDCP. The energy profile showed that barrier energy was roughly 58.1 kcal/mol and 138.6 kcal/mol for NDCS-(H2O)5 and NDCP-(H2O)5 respectively. Proton transfer in NDCS-(H2O)5 generated a lower energy-barrier than the one in NDCP-(H2O)5

scholarly journals Water Adsorption on the β-Dicalcium Silicate Surface from DFT Simulations: a Dual Nucleophilic-Electrophilic Interaction

2018 ◽  
Author(s):  
Qianqian Wang ◽  
Hegoi Manzano ◽  
Iñigo López-Arbeloa ◽  
Xiadong Shen
Keyword(s):  
Density Functional ◽  
Structural Changes ◽  
Water Adsorption ◽  
Lone Pair ◽  
Dicalcium Silicate ◽  
Partial Density ◽  
Surface Sites ◽  
Key Factor ◽  
Charge Analysis ◽  
Oxygen Lone Pair

β-dicalcium silicate (β-Ca2SiO4, or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration speed would be the key point for developing environmentally friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β-C2S surface interactions. Therefore, in this work we aim to understand the water adsorption and dissociation mechanism on the β-C2S (100) surface using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption process takes place in several surface sites, with a broad range of adsorption energies (-0.78 to -1.24 eV), depending on the particular water conformation and surface site. To clarify the key factor governing the adsorption, the electronic properties of water at the surface sites were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with β-C2S (100) surface: a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms, and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms, being the first one the stronger interaction. Hence, we suggest that β-C2S hydration could be enhanced by introducing chemical or structural changes that increase both the electronegative/positive character of the surface.

AIM and NBO analyses on the interaction between SWCNT and cyclophosphamide as an anticancer drug: A density functional theory study

2015 ◽  
Vol 14 (03) ◽  
pp. 1550021 ◽  
Author(s):  
Zahra Felegari ◽  
Majid Monajjemi
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Density Functional ◽  
Energy Gap ◽  
Chemical Shift Anisotropy ◽  
Lone Pair ◽  
Covalent Bond ◽  
Nbo Analysis ◽  
Molecular Structures ◽  
The Stability

In this work, the molecular structures of single-walled carbon nanotube (SWCNT), cyclophosphamide and cyclophosphamide–SWCNT complex were optimized B3LYP/6–31G* level of theory. The nanotube used in this study was a (5,5) SWCNT including 150 C atoms. The NBO analysis showed that the transfer electron can be occurred from the lone pair of oxygen (donor atom) in the cyclophosphamide to the σ* or π* orbitals of the carbon atoms (acceptor atoms) in the SWCNT. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and energy gap (HOMO–LUMO) were calculated for the studied structures and the results indicated the stability of the complex. In addition, the calculated chemical shift isotropy (σ) and the chemical shift anisotropy (Δσ) confirmed the interaction between cyclophosphamide and SWCNT. Also, the results of the atoms in molecule (AIM) theory indicated that the H 145– O 164 bond is a partial covalent bond.

scholarly journals Visible Light-Induced Homolytic Cleavage of Perfluoroalkyl Iodides Mediated by Phosphines

Molecules ◽  
2020 ◽  
Vol 25 (7) ◽  
pp. 1606 ◽  
Author(s):  
Mario Bracker ◽  
Lucas Helmecke ◽  
Martin Kleinschmidt ◽  
Constantin Czekelius ◽  
Christel M. Marian
Keyword(s):  
Visible Light ◽  
Density Functional ◽  
Experimental Studies ◽  
Lone Pair ◽  
Functional Theory ◽  
Computational Evaluation ◽  
Light Region ◽  
Condon Factors ◽  
Oxygen Lone Pair ◽  
Franck Condon

In an effort to explain the experimentally observed variation of the photocatalytic activity of t Bu 3 P, n Bu 3 P and (MeO) 3 P in the blue-light regime [Helmecke et al., Org. Lett. 21 (2019) 7823], we have explored the absorption characteristics of several phosphine– and phosphite–IC 4 F 9 adducts by means of relativistic density functional theory and multireference configuration interaction methods. Based on the results of these computational and complementary experimental studies, we offer an explanation for the broad tailing of the absorption of t Bu 3 P-IC 4 F 9 and (MeO) 3 P-IC 4 F 9 into the visible-light region. Larger coordinate displacements of the ground and excited singlet potential energy wells in n Bu 3 P-IC 4 F 9 , in particular with regard to the P–I–C bending angle, reduce the Franck–Condon factors and thus the absorption probability compared to t Bu 3 P-IC 4 F 9 . Spectroscopic and computational evaluation of conformationally flexible and locked phosphites suggests that the reactivity of (MeO) 3 P may be the result of oxygen lone-pair participation and concomitant broadening of absorption. The proposed mechanism for the phosphine-catalyzed homolytic C–I cleavage of perfluorobutane iodide involves S1 ← S0 absorption of the adduct followed by intersystem crossing to the photochemically active T 1 state.

Electronic structure theory study of the reactivity and structural molecular properties of halo-substituted (F, Cl, Br) and heteroatom (N, O, S) doped cyclobutane

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Moses M. Edim ◽  
Hitler Louis ◽  
Emmanuel A. Bisong ◽  
Apebende G. Chioma ◽  
Obieze C. Enudi ◽  
...  
Keyword(s):  
Electrostatic Potential ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Molecular Electrostatic Potential ◽  
Population Analysis ◽  
Lone Pair ◽  
Nbo Analysis ◽  
Structure Theory ◽  
Potential Energy Distribution ◽  
Distribution Analysis

Abstract Cyclobutane and its halo-substituted derivatives and its heteroatom doped derivatives have been extensively investigated in this study because of the vast applications and interesting chemistry associated with them, the vibrational assignments, Natural Bond Orbital (NBO) analysis, Conceptual Density Functional Theory, Quantum Mechanical Descriptors and Molecular Electrostatic Potential (MEP) analysis have been explored in this study. The corresponding wavenumbers of the studied compounds have as well been assigned by Potential Energy Distribution analysis. Several inter and intramolecular hyperconjugative interactions within the studied compounds have been revealed by the NBO analysis with a confirmation of geometric hybridization and electronic occupancy. The compounds reactivity was observed to decrease down the halo group in manners such as the stability, both were observed to decrease from azetidine to thietane. The distribution of charge was observed to be affected by the ring substituent as observed from the charge population analysis; in addition, adjacent atoms are very much affected by the inherent properties of the substituted atoms. The NBO result suggests that the molecules are stabilized by lone pair delocalization of electrons from the substituted atoms and molecular electrostatic potential (MEP) studies revealed that substituted halogens and doped heteroatoms are important and most probable sites of electrostatic interactions.

scholarly journals Boron-Doped MXenes as Electrocatalysts for Nitrogen Reduction Reaction: A Theoretical Study

2021 ◽  
Vol 3 ◽  
Author(s):  
Yuan Wang ◽  
Xu Qian ◽  
Guokui Zheng ◽  
Ziqi Tian ◽  
Qiuju Zhang
Keyword(s):  
Triple Bond ◽  
Density Functional ◽  
Rational Design ◽  
Surface Composition ◽  
Lone Pair ◽  
Catalytic Performance ◽  
Reduction Reaction ◽  
Nitrogen Reduction ◽  
Boron Doped ◽  
Reduction Catalysts

Electrocatalytic nitrogen reduction reaction (NRR) is a promising and sustainable approach for ammonia production. Since boron as an active center possesses electronic structure similar to that of transition metals with d-orbitals (J. Am. Chem. Soc., 2019, 141 (7), 2884), it is supposed to be able to effectively activate the triple bond in N2. MXenes can be applied as substrates due to the large specific surface area, high conductivity, and tunable surface composition. In this work, the catalytic performance of a series of MXenes-supported single boron atom systems (labeled as B@MXenes) has been systematically studied by using density functional theory (DFT). B@Nb4C3O2, B@Ti4N3O2, and B@Ti3N2O2 were screened out owing to outstanding catalytic activity with limiting potentials of −0.26, −0.15, and −0.10 V, respectively. Further analysis shows that the unique property of boron that can intensely accept lone pair and back-donate the anti-bond of nitrogen contributes to the activation of inert triple bond. This work provides a new idea for the rational design of NRR catalyst and is of great significance for the future development of nitrogen reduction catalysts.

scholarly journals Water Adsorption on the β-Dicalcium Silicate Surface from DFT Simulations

Minerals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 386 ◽  
Author(s):  
Qianqian Wang ◽  
Hegoi Manzano ◽  
Iñigo López-Arbeloa ◽  
Xiaodong Shen
Keyword(s):  
Density Functional ◽  
Water Adsorption ◽  
Lone Pair ◽  
Dicalcium Silicate ◽  
Atomic Scale ◽  
Partial Density ◽  
Key Factor ◽  
Charge Analysis ◽  
Adsorption Energies ◽  
Oxygen Lone Pair

β-dicalcium silicate (β-Ca2SiO4 or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration rate would be the key point for developing environmentally-friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β-C2S surface interactions. In this work, we aim to evaluate the water adsorption on three β-C2S surfaces at the atomic scale using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption takes place in several surface sites with a broad range of adsorption energies (−0.78 to −1.48 eV) depending on the particular mineral surface and adsorption site. To clarify the key factor governing the adsorption of the electronic properties of water at the surface were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with a β-C2S (100) surface including a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms. Despite the elucidation of the adsorption mechanism, no correlation was found between the electronic structure and the adsorption energies.

Theoretical investigation on the structures and bonding properties of Pd(II), Pt(II) and Ni(II) complexes with tridentate CNC-pincer N-heterocyclic carbene ligands

2016 ◽  
Vol 15 (05) ◽  
pp. 1650037 ◽  
Author(s):  
Fen He ◽  
Xin Yang ◽  
Zhi-Yue Tian ◽  
Han-Guang Wang ◽  
Ying Xue
Keyword(s):  
Density Functional ◽  
Energy Levels ◽  
Lone Pair ◽  
Nbo Analysis ◽  
Central Metal ◽  
The Density Functional Theory ◽  
Bonding Properties ◽  
Group 10 Metals ◽  
Back Donation

The density functional theory (DFT) has been applied for the analysis of the bond between group 10 metals and N-heterocyclic carbene (NHC) in complexes (MCl(L-X): M [Formula: see text] Pd(II), Pt(II), and Ni(II), L-X[Formula: see text][2-(3-methylimidazolin-4,5-bisX-2-yliden-1-yl)-4-phenyl] amido, X [Formula: see text]H, Cl and CN). Full geometry optimizations have been performed for all the ligands (L-X[Formula: see text] anions), MCl[Formula: see text] cations, and the complexes. In the ligands, the energy levels of the carbon [Formula: see text] lone-pair orbitals suggest the trend L-H[Formula: see text] L-Cl[Formula: see text] L-CN[Formula: see text] for the donor strength. The role of the M–NHC interaction in complexes was investigated by natural bond orbital (NBO) analysis. The results show that the NHC–M bond consists of the components originating from the L[Formula: see text]M donation and the M[Formula: see text]Carbene C back-donation and the metal[Formula: see text]the ring of NHC back-donation. The transition-metal strongly affects the donation and back-donation. The interaction between the metal and the NHC ligand can be influenced by the central metal and the substituent on the ring of NHC.

scholarly journals Water Adsorption on the β-Dicalcium Silicate Surface from DFT Simulations

2018 ◽  
Author(s):  
Qianqian Wang ◽  
Hegoi Manzano ◽  
Iñigo López-Arbeloa ◽  
Xiadong Shen
Keyword(s):  
Density Functional ◽  
Water Adsorption ◽  
Lone Pair ◽  
Dicalcium Silicate ◽  
Atomic Scale ◽  
Partial Density ◽  
Key Factor ◽  
Charge Analysis ◽  
Adsorption Energies ◽  
Oxygen Lone Pair

β-dicalcium silicate (β-Ca2SiO4, or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration rate would be the key point for developing environmentally friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β-C2S surface interactions. In this work we aim to evaluate the water adsorption on three β-C2S surfaces at the atomic scale using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption takes place in several surface sites, with a broad range of adsorption energies (−0.78 to −1.48 eV), depending on the particular mineral surface and adsorption site. To clarify the key factor governing the adsorption, the electronic properties of water at the surface were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with β-C2S (100) surface: a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms, and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms. Despite the elucidation of the adsorption mechanism, no correlation was found between the electronic structure and the adsorption energies.

Density functional theory, Comparative vibrational spectroscopic studies, HOMO-LUMO, and NBO analysis of Trichloro isocyanuric acid and Trithio cyanuric acid

2015 ◽  
Vol 8 (3) ◽  
pp. 2197-2221
Author(s):  
Theraviyum Chithambarathanu ◽  
M. Darathi ◽  
J. DaisyMagdaline ◽  
S. Gunasekaran
Keyword(s):  
Density Functional ◽  
Cyanuric Acid ◽  
Nbo Analysis ◽  
Basis Set ◽  
Potential Energy Distribution ◽  
Point Energy ◽  
Isocyanuric Acid ◽  
Ft Ir ◽  
Homo Lumo ◽  
Ft Raman

The molecular vibrations of Trichloro isocyanuric acid (C3Cl3N3O3) and Trithio cyanuric acid (C3H3N3S3) have been investigated in polycrystalline sample at room temperature by Fourier Transform Infrared (FT-IR) and FT-Raman spectroscopies in the region 4000-450 cm-1 and 4000-50 cm-1 respectively, which provide a wealth of structural information about the molecules. The spectra are interpreted with the aid of normal co-ordinate analysis following full structure optimization and force field calculations based on density functional theory   (DFT) using standard B3LYP / 6-311++ G (d, p) basis set for investigating the structural and spectroscopic properties. The vibrational frequencies are calculated and the scaled values are compared with experimental FT-IR and FT-Raman spectra. The scaled theoretical wave numbers shows very good agreement with experimental ones. The complete vibrational assignments are performed on the basis of potential energy distribution (PED) of vibrational modes, calculated with scaled quantum (SQM) method. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that change in electron density (ED) in σ* and π* anti-bonding orbitals and second order delocalization   energy (E2) confirm the occurrence of Intra molecular Charge Transfer (ICT) within the molecule. The thermodynamic properties like heat capacity, entropy, enthalpy and zero point energy have been calculated for the molecule. The frontier molecular orbitals have been visualized and the HOMO-LUMO energy gap has been calculated. The Molecular Electrostatic Potential (MEP) analysis reveals the sites for electrophilic attack and nucleophilic reactions in the molecule.

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