Detailed Density Functional Theory Study Research Articles

Excited-state intramolecular proton transfer mechanism for 2-(quinolin-2-yl)-3-hydroxychromone: A detailed time-dependent density functional theory study

In this work, the Excited-state intramolecular proton transfer mechanism of 2-(quinolin-2-yl)-3-hydroxychromone (Q3HC) in 1,2-dichloroethane solvent have been investigated via the density functional (DFT) and the time-dependent density functional theory (TDDFT) method. By calculation, we optimize three configurations (Q3HC-A, Q3HC-B and Q3HC-C) and find the phenomenon of converting between Q3HC-B and Q3HC-A in the S0 and S1 states. Based on comparing the primary bond lengths, bond angles and infrared vibrational spectra involved in the hydrogen bonds between S0 and S1 states, hydrogen bonds strengthening in the S1 state have been testified. The calculated absorption and fluorescence spectra of Q3HC-A, Q3HC-B and Q3HC-C are agreement with the experimental data, and the results also show that the tautomer form of Q3HC-C has a fluorescence spectrum, which is different from the previous report (Svechkarev et al., Journal of Luminescence, 2011, 131, 253–261). Meanwhile, we also constructed the potential energy curves of S0 and S1 states, and further explained the ESIPT mechanism of Q3HC-A, Q3HC-B and Q3HC-C, respectively. These results have shown that the ESIPT of Q3HC-C is a barrierless process, which occurs more easily than that of Q3HC-A and Q3HC-B. Combination with reduced density gradient function, the hydrogen bond of Q3HC-C is strongest, compared with Q3HC-A and Q3HC-B. And it also can provide the real evidence that the ESIPT of Q3HC-C is more favorable than that of Q3HC-A and Q3HC-B.

Can Supported Reduced Vanadium Oxides form H2 from CH3OH? A Computational Gas-Phase Mechanistic Study.

A detailed density functional theory study is presented to clarify the mechanistic aspects of the methanol (CH3OH) dehydrogenation process to yield hydrogen (H2) and formaldehyde (CH2O). A gas-phase vanadium oxide cluster is used as a model system to represent reduced V(III) oxides supported on TiO2 catalyst. The theoretical results provide a complete scenario, involving several reaction pathways in which different methanol adsorption sites are considered, with presence of hydride and methoxide intermediates. Methanol dissociative adsorption process is both kinetically and thermodynamically feasible on V-O-Ti and V═O sites, and it might lead to form hydride species with interesting catalytic reactivity. The formation of H2 and CH2O on reduced vanadium sites, V(III), is found to be more favorable than for oxidized vanadium species, V(V), taking place along energy barriers of 29.9 and 41.0 kcal/mol, respectively.

A novel luminescent ionic trinuclear Cu3I2 cluster cuprous complex supported by a P^N ligand: synthesis, structure characterization, properties and TD-DFT calculations.

Luminescent cuprous complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The title ionic trinuclear Cu3I2 complex, tris[μ2-diphenyl(pyridin-2-yl)phosphane-κ2P:N]di-μ3-iodido-tricopper(I)(3 Cu-Cu) hexafluoridophosphate, [Cu3I2(C39H32NP)3]PF6, conventionally abbreviated as [Cu3I2(Ph2PPy)3]PF6, is described. Each CuI atom is coordinated by two μ3-iodide ligands and by a P and an N atom from two Ph2PPy ligands, giving rise to a CuI2PN tetrahedral coordination geometry about each CuI centre. The electronic absorption and photoluminescence properties of this trinuclear cluster have been studied on as-synthesized samples, which had been examined previously by powder X-ray diffraction. A detailed time-dependent density functional theory (TD-DFT) study was carried out and showed a green emission derived from a halide-to-ligand charge transfer and metal-to-ligand charge transfer 3(X+M)LCT excited state.

DFT Study on Intermetallic Pd-Cu Alloy with Cover Layer Pd as Efficient Catalyst for Oxygen Reduction Reaction.

Detailed density functional theory (DFT) calculations of the adsorption energies (Ead) for oxygen on monolayer Pd on top of the Pd–Cu face-centered cubic (FCC) alloy and intermetallic B2 structure revealed a linear correspondence between the adsorption energies and the d-band center position. The calculated barrier (Ebarrier) for oxygen dissociation depends linearly on the reaction energy difference (ΔE). The O2 has a stronger adsorption strength and smaller barrier on the intermetallic Pd–Cu surface than on its FCC alloy surface. The room-temperature free energy (ΔG) analysis suggests the oxygen reduction reaction (ORR) pathways proceed by a direct dissociation mechanism instead of hydrogenation into OOH. These results might be of use in designing intermetallic Pd–Cu as ORR electrocatalysts.

Potential of metal–fullerene hybrids as strong nanocarriers for cytosine and guanine nucleobases: A detailed DFT study

In this article, the adsorption of cytosine and guanine molecules on the surface of Cr-doped C20 fullerene (C19Cr) and Ni-doped C20 fullerene (C19Ni) are studied using first-principles density functional theory (DFT) calculations. In order to thoroughly comprehend the influences of the molecules on the metal-fullerene complexes, the geometric parameters, the binding energies, transferred charges, the magnitude of dipole moments, thermochemical parameters, frontier molecular orbitals, and the global indices of activities are calculated. The results highlighted that the interactions of both cytosine and guanine molecules with metal-fullerene complexes are highly exothermic, suggesting that these molecules might be chemisorbed on their adsorbents. The C19Cr exhibits a better adsorption behavior toward the molecules compared to C19Ni, and cytosine has the higher binding energies with metal-fullerene complexes in comparison with guanine. Further analyses showed that the C19Cr experiences significant changes in its electronic properties upon adsorption of the cytosine molecule. However, the small variations in the electronic properties of C19Ni after complexation with guanine indicate that this complex is not sensitive to the guanine. Furthermore, the results of frontier molecular orbital reveal the strong (moderate) interactions between the C19Cr with the cytosine (guanine) molecule and moderate (weak) interactions between the C19Ni with the cytosine (guanine) molecule. Therefore, the C19Cr and C19Ni have moderate sensitivities to cytosine and guanine molecules. More excitingly, our findings divulge promising potential of the Cr-fullerene complex as a biochemical adsorbent for cytosine.

Impact of zeolite-Y framework on the geometry and reactivity of Ru (III) benzimidazole complexes – A DFT study

A detailed comparative Density Functional Theory (DFT) study is made to understand the structural changes of the guest complex due to steric and electronic interactions with the host framework. In this study, Ru(III) benzimidazole and 2- ethyl Ru(III) benzimidazole complexes encapsulated in a supercage of zeolite Y. The zeolitic framework integrity is not disturbed by the intrusion of the large guest complex. A blue shift in the d–d transition observed in the UV-Visible spectroscopic studies of the zeolite encapsulated complexes and they shows a higher catalytic efficiency. Encapsulation of zeolite matrix makes the metal center more viable to nucleophilic attack and favors the phenol oxidation reaction. Based on the theoretical calculations, transition states and structures of reaction intermediates involved in the catalytic cycles are derived.

Winged-Cone Conformation in Hexa-p-tert-butylcalix[6]arene Driven by the Unusually Strong Guest Encapsulation.

Hexa-p-tert-butylcalix[6]arene (1) is believed to adopt a winged conformation in a solution, featured by four phenyl rings perpendicular to the calix basis and two others at 1,4-positions lying down. However, there is some controversy on the occurrence of this conformation because it has never been found in the solid state of calix[6]arenes, regardless of the substitution pattern at lower and upper rims. Here, we have observed the winged-cone conformation for the first time in a solvate form of 1 with dimethyl sulfoxide (DMSO), dimethylformamide, and pyridine. The DMSO molecule is strongly encapsulated into 1 through two OH···O hydrogen bonds with both flattened phenolic moieties, one lp(S)···π and four CH···π interactions with the four perpendicular phenyl rings. This host–guest complex has energy lower by 23.4 kcal mol–1 than the isolated species. In addition, another DMSO solvate form with 1,2,3-alternate conformation was also obtained in this study, and its structure is compared with that of the precedent one. A detailed density functional theory study has also been carried out to understand the energetic relationships among cone conformers, intramolecular hydrogen-bonding patterns, and DMSO encapsulation.

Density Functional Theory Study of the Thermodynamic and Raman Vibrational Properties of γ-UO3 Polymorph

Gamma uranium trioxide, γ-UO3, is one of the most important polymorphs in uranium trioxide system, which is common throughout the nuclear fuel cycle and used industrially in the reprocessing of nuclear fuel and uranium enrichment. In this work, a detailed theoretical solid-state density functional theory study of this material was carried out. The computed lattice parameters, bond lengths, bond angles, and X-ray powder pattern were found in very good agreement with their experimental counterparts determined by X-ray diffraction. The equation of state of γ-UO3 was obtained, and therefore, the values of the bulk modulus and its derivatives, for which there are not experimental data to compare with, were predicted. The computed bulk modulus differs from that of a previous density functional theory calculation by only 4.4%. The thermodynamic properties of this material, including heat capacity, entropy, enthalpy, free energy, and Debye temperature were also determined as a function of temperature in the range...

Experimental and Theoretical Studies on Rhodium-Catalyzed Coupling of Benzamides with 2,2-Difluorovinyl Tosylate: Diverse Synthesis of Fluorinated Heterocycles.

Fluorinated heterocycles play an important role in pharmaceutical and agrochemical industries. Herein, we report on the synthesis of four types of fluorinated heterocycles via rhodium(III)-catalyzed C-H activation of arenes/alkenes and versatile coupling with 2,2-difluorovinyl tosylate. With N-OMe benzamide being a directing group (DG), the reaction delivered a monofluorinated alkene with the retention of the tosylate functionality. Subsequent one-pot acid treatment allowed the efficient synthesis of 4-fluoroisoquinolin-1(2H)-ones and 5-fluoropyridin-2(1H)-ones. When N-OPiv benzamides were used, however, [4 + 2] cyclization occurred to provide gem-difluorinated dihydroisoquinolin-1(2H)-ones. Synthetic applications have been demonstrated and the ready availability of both the arene and the coupling partner highlighted the synthetic potentials of these protocols. Mechanistically, these two processes share a common process involving N-H deprotonation, C-H activation, and olefin insertion to form a 7-membered rhodacycle. Thereafter, different reaction pathways featuring β-F elimination and C-N bond formation are followed on the basis of density functional theory (DFT) studies. These two pathways are DG-dependent and led to the open chain and cyclization products, respectively. The mechanistic rationale was supported by detailed DFT studies. In particular, the origins of the intriguing selectivity in the competing β-F elimination versus C-N bond formation were elucidated. It was found that β-F elimination is a facile event and proceeds via a syn-coplanar transition state with a low energy barrier. The C-N bond formation proceeds via a facile migratory insertion of the Rh-C(alkyl) into the Rh(V) amido species. In both reactions, the migratory insertion of the alkene is turnover-limiting, which stays in good agreement with the experimental studies.

The adsorption of Cu on the CeO2(110) surface.

We report a detailed density functional theory (DFT) study in conjunction with extended X-ray absorption fine structure (EXAFS) experiments on the geometrical and local electronic properties of Cu adatoms and Cu(ii) ions in presence of water molecules and of CuO nanoclusters on the CeO2(110) surface. Our study of (CuO)n(=1,2&4) clusters on CeO2(110) shows that based on the Cu-O environment, the geometrical properties of these clusters may vary and their presence may lead to relatively high localization of charge on the exposed surfaces. We find that in the presence of an optimum concentration of water molecules, Cu has a square pyramidal geometry, which agrees well with our experimental findings; we also find that Cu(ii) facilitates water adsorption on the CeO2(110) surface. We further show that a critical concentration of water molecules is required for the hydrolysis of water on Cu(OH)2/CeO2(110) and on pristine CeO2(110) surfaces.

Copper-Mediated Selective Hydroxylation of a Non-activated C-H Bond in Steroids: A DFT Study of Schönecker's Reaction.

The regio- and stereoselective copper-mediated hydroxylation of a non-activated aliphatic C-H bond in steroids by dioxygen, initially reported by Schönecker et al. (Angew. Chem. Int. Ed. 2003, 42, 3240-3244), has recently evolved into a valuable synthetic tool. In the present work, a detailed mechanistic density functional theory (DFT) study addressing the origin of the remarkable selectivity of Schönecker's reaction is reported. The applied BLYP-D3/def2-TZVP(SDD) level of DFT is benchmarked against experimental and coupled-cluster reference data. The resulting mechanistic scenario involves formation of a bis-μ-oxo dicopper complex as key intermediate. In this complex three C-H bonds of the pendant steroid ligand are predisposed towards intramolecular activation by the bis-μ-oxo dicopper core. The lowest activation barrier (12.0 kcal mol-1 ) is computed for β-hydroxylation at the C12 position, in agreement with the experimental observations. Natural bond orbital (NBO) analysis reveals stabilizing orbital interactions that favor the β-hydroxylation pathway over competing reaction channels.

DFT studies on the structural and vibrational properties of polyenes.

Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C = C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C = C) and ν(C–C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon–carbon double bonds were used to estimate these values for very long chains. Correction of raw, unscaled vibrational data was performed by comparing theoretical and experimental wavenumbers for polyenes chains containing 3 to 12 conjugated C = C units with both ends substituted by tert-butyl groups. The corrected ν(C = C) and ν(C–C) wavenumbers for all-trans molecules were used to estimate the presence of 9 – 12 C = C units in all-trans polyene pigment in red coral.Graphical abstractDetailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C=C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae.Electronic supplementary materialThe online version of this article (doi:10.1007/s00894-016-2969-1) contains supplementary material, which is available to authorized users.

DFT studies on the origin of regioselective ring-opening of terminal epoxides during copolymerization with CO2

This report presents a detailed density functional theory (DFT) study on the difference in regioselectivity for the copolymerization reactions of styrene oxide versus propylene oxide with CO2 utilizing binary (salen)cobalt(III) catalyst systems. This study focuses on the discrepancy of regioselective ring-opening of two terminal epoxides during the copolymerization with CO2. It was found that the nucleophilic ring-opening of styrene oxide occurred predominantly at the methine C α -O bond due to the election delocalization of phenyl group to stabilize the transition state for the methine C―O bond cleavage.

Structural evolution, electronic and magnetic manners of small rhodium Rhn+/−(n = 2–8) clusters: a detailed density functional theory study

We have evaluated the stable electronic structure and magnetic properties of all neutral and ionic Rhn(n= 2–8) clusters using density functional theory. This study reveals that Rh4is the magic cluster based on the calculated reactivity parameters.

A computational and experimental re-examination of the reaction of the benzyloxyl radical with DMSO

A detailed density-functional theory study on the reaction of the benzyloxyl radical (BnO) with dimethyl sulfoxide (DMSO) was performed. The calculations reveal that BnO transfers a hydrogen atom to DMSO via a proton-coupled electron transfer reaction to form benzaldehyde, in agreement with the mechanism proposed in the literature for the reaction of ethoxyl radical with substituted pyridines. The radical formed from this reaction, DMSO-H, is predicted to be unstable owing to population of the SO antibonding π-orbital and decompose without barrier to form dimethyl sulfide and hydroxyl radical. The calculated exergonicity of the reaction is 16.6kcal/mol. Our previous laser-flash photolysis (LFP) studies reported a kinetic deuterium isotope effect (KDIE), kH(DMSO)/kD(DMSO-d6), of 0.91 for this reaction, which is consistent with the foregoing mechanism, and with the value calculated in this work of 0.77. New LFP data reported herein for the reaction of BnO-d2 with DMSO give an experimental KDIE of 3.06, compared with a calculated value of 2.8. Taken collectively, our computational and experimental re-examination of the reaction between BnO and DMSO leads to the conclusion that BnO transfers a hydrogen atom to, rather than abstracts a hydrogen atom from, DMSO.

Electronic Structure of IrO2: The Role of the Metal d Orbitals

IrO2 is one of the most active catalysts for the oxygen evolution reaction (OER) and remains the only known stable OER catalyst in acidic conditions. As a first step in understanding the mechanism for OER we carried out detailed Density Functional Theory (DFT) studies of the electronic structure of IrO2. We compared the electronic states and magnetic properties of IrO2 using several density functionals. We found that DFT with hybrid functionals (B3PW and PBE0) leads to a weak ferromagnetic coupling, although IrO2 has often been reported as nonmagnetic. We also found a magnetic ground state for RuO2, whose electronic structure is similar to that of IrO2. Ru–Ru antiferromagnetic interaction has been observed experimentally in nanoparticle RuO2. Further low temperature measurements are necessary to confirm whether a weak magnetism may occur below 20 K in IrO2. We also found that PBE leads to a better agreement with the experimental XPS spectra, compared with hybrid functionals and PBE+U.

Localized versus itinerant states created by multiple oxygen vacancies in SrTiO3

Oxygen vacancies in strontium titanate surfaces (SrTiO3) have been linked to the presence of a two-dimensional electron gas with unique behavior. We perform a detailed density functional theory study of the lattice and electronic structure of SrTiO3 slabs with multiple oxygen vacancies, with a main focus on two vacancies near a titanium dioxide terminated SrTiO3 surface. We conclude based on total energies that the two vacancies preferably inhabit the first two layers, i.e. they cluster vertically, while in the direction parallel to the surface, the vacancies show a weak tendency towards equal spacing. Analysis of the nonmagnetic electronic structure indicates that oxygen defects in the surface TiO2 layer lead to population of Ti states and thus itinerancy of the electrons donated by the oxygen vacancy. In contrast, electrons from subsurface oxygen vacancies populate Ti eg states and remain localized on the two Ti ions neighboring the vacancy. We find that both the formation of a bound oxygen-vacancy state composed of hybridized Ti 3eg and 4p states neighboring the oxygen vacancy as well as the elastic deformation after extracting oxygen contribute to the stabilization of the in-gap state.

Detailed DFT studies of the band profiles and optical properties of antiperovskites SbNCa3 and BiNCa3

Structural, electronic and optical properties of antiperovskite compounds, SbNCa3 and BiNCa3, are studied by using the full-potential linearized augmented plane waves (FP-LAPW) method under the framework of density functional theory (DFT). The exchange–correlation potential is treated by local density approximation (LDA), generalized gradient approximation (GGA-PBEsol) and GGA developed by Engel and Vosko (EV-GGA). Furthermore, the modified Becke–Johnson (mBJ) potential is also applied to attain reliable results for the band gaps of these compounds. The calculated lattice constants are found consistent with the experimentally measured values and other theoretical results. The band profiles show that both of these materials are direct band gap semiconductors of about 1.1eV gap. The direct band gap nature reveals that they may be effective in optical devices and therefore the optical properties of these compounds like the real and imaginary parts of dielectric function, refractive index and absorption coefficient are also calculated and discussed.

Inner- versus Outer-Sphere Ru-Catalyzed Formic Acid Dehydrogenation: A Computational Study

A detailed hybrid density functional theory study was carried out to clarify the mechanism of Ru-catalyzed dehydrogenation of formic acid in the presence of the octahedral complexes [Ru(κ4-NP3)Cl2]...

Taming the shrew: [TMEDALi-Zn(C2H4)2L] as a model compound for anionic ethene polymerisation

We describe the synthesis of the compound [(TMEDA)Li(μ-TMP)(μ-CHCH2)Zn(C2H3)] (1) (TMEDA = N,N,N′,N′-tetramethylethylenediamine, TMP = 2,2,6,6-tetramethylpiperidide), which serves as a potential model compound for anionic ethene polymerisation, and its decomposition into the metallated compound [Li(μ-Me2NCH2CH2N(Me)CH2)(μ-TMP)Zn(C2H3)] (4). The previously reported compound [(PMDETA)K(μ-TMP)(μ-CHCH2)-Zn(CH2SiMe3)] (2) (PMDETA = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) and 1 are used as potential model compounds for anionic ethene polymerisation. Detailed Density Functional Theory (DFT) at the B3LYP/6-311G(d,p) level of theory on both 1 and 2 in conjunction with Bader AIM and NBO analyses revealed a substantial interaction between the Zn–CH atom and the Li (in 1, dLi–CH = 2.43 A) or K (in 2, dK–CH = 3.01 A). In fact, in the case of 1, this interaction is even stronger (estimated to be 20–30 kJ mol−1) than those reported in the previously reported DFT studies of the reaction with butyl lithium and ethene in the presence of diamino ligands. Our theoretical results are in good agreement with experimentally observed parameters.