Correlation found between the HOMO–LUMO energy separation and the chemical reactivity at the most reactive site for isolated-pentagon isomers of fullerenes

Aihara, Jun‐ichi

doi:10.1039/b002601h

Cited by 140 publications

(93 citation statements)

References 28 publications

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“…The knowledge about the electronic structure of urea in solution, however, is crucial for a deeper understanding of its behavior in chemical reactions. In particular, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is of large interest since it serves as indicator for molecular properties like stability or reactivity (see, e.g., references [16][17][18][19] and references therein). The HOMO-LUMO gap itself, however, is strongly affected by an exchange of the functional groups of a molecule.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

Tesch

Golnak

Ehrhard

et al. 2016

Chemistry A European J

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Soft X-ray emission, absorption, and resonant inelastic scattering experiments have been conducted at the nitrogen K-edge of urea and its derivatives in aqueous solutions and compared with density functional theory and time-dependent density functional theory calculations. This comprehensive study provides detailed information on the occupied and unoccupied molecular orbitals of urea, thiourea, acetamide, dimethylurea and biuret at valence levels. By identifying the electronic transitions that contribute to the experimental spectral features the energy gap between the highest occupied and the lowest unoccupied molecular orbital of each molecule is determined. Moreover, a theoretical approach is introduced to simulate resonant inelastic X-ray scattering spectra by adding an extra electron to the lowest unoccupied molecular orbital mimicking the real initial state of the core electron absorption before the subsequent relaxation process.

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Section: Introductionmentioning

confidence: 99%

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

Tesch

Golnak

Ehrhard

et al. 2016

Chemistry A European J

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“…From a catalytic perspective, systems with smaller HOMO-LUMO gaps tend to be more reactive. 74,75 In Table 2 we report the HOMO-LUMO gaps for the clusters studied here, both with and without adsorbed CO. The results obtained for the HOMO-LUMO gap for the metal clusters before CO adsorption are identified as "bare" clusters.…”

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confidence: 99%

CO Adsorption on Noble Metal Clusters: Local Environment Effects

et al. 2011

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Bimetallic catalysts are useful because of their versatility, such as the ability to tune their catalytic activity and selectivity by varying properties such as composition, particle size, and support. 1 In particular, Pt-Au catalysts have been shown to exhibit enhanced activity and selectivity in specific reactions when compared to monometallic catalysts. For example, Dimitratos et al. 2 showed that carbon-supported Pt-Au has higher catalytic activity for the oxidation of glycerol than carbon-supported Pt and that the catalyst preparation method affects the selectivity. Selvarani et al. 3 determined that the optimum Pt:Au ratio for carbon-supported Pt-Au as a direct methanol fuel cell catalyst is 2:1, at which composition the catalyst delivers a peak power density 1.5 times that of pure Pt. Comotti et al. 4 found a turnover frequency of 60 h -1 for the oxidation of glucose over pure platinum, while a Pt-Au alloy with Au:Pt ratio of 2:1 yields a turnover frequency of 924 h -1 . The authors also found that, for 7 different Au:Pt ratios ranging from 4 to 0.25, the minimum and maximum turnover frequencies are 240 and 924 h -1 , observed for Au:Pt ratios of 1 and 2, respectively. It is likely that these results depend on the atomic arrangement on the surface of the bimetallic nanoparticles used as catalysts. Unfortunately, direct experimental visualization of the composition and structure of nanoparticle surfaces is at present problematic, especially at operating conditions. Techniques such as high-energy resonant X-ray diffraction can be used to probe the structure of bimetallic catalysts. 5 Molecular simulations could be useful to interpret such experiments and also identify the local structure of supported mono-and bimetallic nanoparticles. [6][7][8] For example, we have previously used molecular dynamics (MD) simulations to study the effect of composition and support geometry on the properties of Pt-Au nanoparticles containing 250 atoms, 9 finding that it should be possible to tailor the distribution of atoms by manipulating nanoparticle composition and support geometry. This could lead to greater control of catalyst selectivity by maximizing the active sites on the nanoparticle surface that catalyze a certain reaction.In order to link our previous MD results to experimentally verifiable measurements, we report here ab initio density functional theory (DFT) calculations for CO adsorption on Pt-Au clusters. CO is often employed as a probe molecule because its adsorption energy and C-O stretching frequency depend on the adsorption site, as can be observed experimentally via, e.g., Fourier transform infrared spectroscopy. 10 CO adsorption is also important in CO oxidation, which occurs in automobile catalytic converters, 11 in preferential CO oxidation (PROX reaction) in hydrogen feeds, 12 and in CO hydrogenation, the critical step in Fischer-Tropsch processes. 13 DFT has been used to study adsorption of CO on metal surfaces, such as Pt(111), [14][15][16][17] on Pt(111) overlayers, 18,19 and on metal nanoparticles. ...

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“…Computed NICS values, shown in Table 1, reveals that all the most stable fullerene isomers B cage seems to have the largest negative NICS value -66.4 ppm with higher than any reported value for boron cages, including the core-shell structure B 101 , B 80 and B 38 cages reported in [13,31]. As an another stability measure, we compute HOMO-LUMO energy gap (E g ) [43][44][45] and they are given in Table 1. The lowest energy isomers B In Table 2, we give the binding energies per atom, the band gaps and NICS values of the well known α-B [12].…”

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confidence: 99%

A new hole density as a stability measure for boron fullerenes

Polad

Özay

2013

Phys. Chem. Chem. Phys.

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We investigate the stability of boron fullerene sets B76, B78 and B82. We evaluate the ground state energies, nucleus-independent chemical shift (NICS), the binding energies per atom and the band gap values by means of first-principles methods. We construct our fullerene design by capping of pentagons and hexagons of B60 cage in such a way that the total number of atoms is preserved. In doing so, a new hole density definition is proposed such that each member of a fullerene group has a different hole density which depends on the capping process. Our analysis reveal that each boron fullerene set has its lowest-energy configuration around the same normalized hole density and the most stable cages are found in the fullerene groups which have relatively large difference between the maximum and the minimum hole densities. The result is a new stability measure relating the cage geometry characterized by the hole density to the relative energy.The geometric structure of boron allotropes in respect to their ground state energy is a subject of great interest. Studies focused on searching the lowest energy configurations has yielded a variety of stable boron structures due to electron deficient nature of boron. Such structures involve molecular wheels [1,2], boron sheets composed of triangular and hexagonal motifs [3][4][5][6][7][8][9][10][11][12] [17,18]. Boron based forms are known for their complex chemistry. Unlike carbon, both pure boron and many boron rich compounds contain B 12 cage structures in their crystalline state. Furthermore, boron crystals show peculiarities such as uncommon 2c-1e and 3c-2e bonding [19] and unique aromaticity [20,21]. Most crystal samples exhibit defects, vacancies and interstitials, due to the flexible bond structure [22]. Among such structures, the newest form, orthorhombic γ-B 28 , is found to be the second hardest elemental material after diamond with a value of 58 GPa [23,24] and has strong covalent interatomic interactions even higher than the intraicosahedral bonds [25].A key concept in stability analysis of boron sheets is the hole density. This is defined as the ratio of the number of hexagonal holes to the number of atoms in the triangular sheet. The so called α-sheet was found to be the most stable boron sheet with η=1/9 [10]. In a recent work, it is shown that hexagonal holes of α-sheet are the scavengers of extra electrons from the filled hexagons [26]: a unique aspect of α-sheet, in conjunction with the hole density, is that the ratio η=1/9 exactly corresponds to the ratio of the extra π electron to the number of σ electrons in a filled hexagon. Boron layers composed of hexagonal hole doped triangular lattices manifest polymorphism [27] i.e. multiple 2D boron layers have comparable stabilities even some of them have lower energy than the α sheet [28,29]. Boron sheets g(1/8), g(2/15), α 1 and α 2 are the examples of such ground state structures. Such correlation between the

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Correlation found between the HOMO–LUMO energy separation and the chemical reactivity at the most reactive site for isolated-pentagon isomers of fullerenes

Cited by 140 publications

References 28 publications

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

CO Adsorption on Noble Metal Clusters: Local Environment Effects

A new hole density as a stability measure for boron fullerenes

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