Institute Of Quimica Computacional I Catalisi Iqcc

Girona, Spain

Institute Of Quimica Computacional I Catalisi Iqcc

Girona, Spain
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Duran M.,Institute Of Quimica Computacional I Catalisi Iqcc | Sola M.,Institute Of Quimica Computacional I Catalisi Iqcc
Journal of Computational Chemistry | Year: 2017

The bonding patterns in coronene are complicated and controversial as denoted by the lack of consensus of how its electronic structure should be described. Among the different proposed descriptions, the two most representative are those generated by Clar's aromatic π-sextet and adaptative natural density partitioning (AdNDP) models. Quantum-chemical calculations at the density functional theory level are performed to evaluate the model that gives a better representation of coronene. To this end, we analyse the molecular structure of coronene, we estimate the aromaticity of its inner and outer rings using various local aromaticity descriptors, and we assess its chemical reactivity from the study of the Diels-Alder reaction with cyclopentadiene. Results obtained are compared with those computed for naphthalene and phenanthrene. Our conclusion is that Clar's π-sextet model provides the representation of coronene that better describes the physicochemical behavior of this molecule. © 2017 Wiley Periodicals, Inc.

Company A.,Institute Of Quimica Computacional I Catalisi Iqcc | Sabenya G.,Institute Of Quimica Computacional I Catalisi Iqcc | Gonzalez-Bejar M.,University of Valencia | Gomez L.,Institute Of Quimica Computacional I Catalisi Iqcc | And 10 more authors.
Journal of the American Chemical Society | Year: 2014

The preparation of [FeIV(O)(MePy2tacn)]2+ (2, MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) by reaction of [FeII(MePy2tacn)(solvent)]2+ (1) and PhIO in CH3CN and its full characterization are described. This compound can also be prepared photochemically from its iron(II) precursor by irradiation at 447 nm in the presence of catalytic amounts of [Ru II(bpy)3]2+ as photosensitizer and a sacrificial electron acceptor (Na2S2O8). Remarkably, the rate of the reaction of the photochemically prepared compound 2 toward sulfides increases 150-fold under irradiation, and 2 is partially regenerated after the sulfide has been consumed; hence, the process can be repeated several times. The origin of this rate enhancement has been established by studying the reaction of chemically generated compound 2 with sulfides under different conditions, which demonstrated that both light and [Ru II(bpy)3]2+ are necessary for the observed increase in the reaction rate. A combination of nanosecond time-resolved absorption spectroscopy with laser pulse excitation and other mechanistic studies has led to the conclusion that an electron transfer mechanism is the most plausible explanation for the observed rate enhancement. According to this mechanism, the in-situ-generated [RuIII(bpy)3] 3+ oxidizes the sulfide to form the corresponding radical cation, which is eventually oxidized by 2 to the corresponding sulfoxide. © 2014 American Chemical Society.

Gruden-Pavlovic M.,University of Belgrade | Stepanovic S.,University of Belgrade | Peric M.,University of Belgrade | Guell M.,Institute Of Quimica Computacional I Catalisi Iqcc | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2014

Density Functional Theory (DFT) was used to analyse and explain spin state energetics of first-row transition metals (MnII, FeII, CoII; CrIII, MnIII, FeIII, Co III; MnIV) in polypyrazolylborato complexes. We explored the effects of substitutions at the 3 and 5 positions of the pyrazolyl rings, as well as the influence of Jahn-Teller (JT) distortions on spin-state switching. Although the stabilizations due to JT distortion are sometimes substantial, this does not lead to switching of the spin ground-state. On the other hand, electron withdrawing or donating substituents do lead to significant changes in the spin-crossover (SCO) properties of the investigated complexes. © the Partner Organisations 2014.

Cioslowski J.,University Of Szczecin | Strasburger K.,Wroclaw University of Technology | Matito E.,Institute Of Quimica Computacional I Catalisi Iqcc
Journal of Chemical Physics | Year: 2014

For a wide range of confinement strengths ω, explicitly-correlated calculations afford approximate energies E(ω) of the ground and low-lying excited states of the four-electron harmonium atom that are within few μhartree of the exact values, the errors in the respective energy components being only slightly higher. This level of accuracy constitutes an improvement of several orders of magnitude over the previously published data, establishing a set of benchmarks for stringent calibration and testing of approximate electronic structure methods. Its usefulness is further enhanced by the construction of differentiable approximants that allow for accurate computation of E(ω) and its components for arbitrary values of ω. The diversity of the electronic states in question, which involve both single- and multideterminantal first-order wavefunctions, and the availability of the relevant natural spinorbitals and their occupation numbers make the present results particularly useful in research on approximate density-matrix functionals. The four-electron harmonium atom is found to possess the 3P+ triplet ground state at strong confinements and the 5S- quintet ground state at the weak ones, the energy crossing occurring at ω ≈ 0.0240919. © 2014 AIP Publishing LLC.

Swart M.,Institute Of Quimica Computacional I Catalisi Iqcc | Swart M.,Catalan Institution for Research and Advanced Studies
Chemical Physics Letters | Year: 2013

A new family of (range-separated) hybrid functionals is presented that corrects several of the shortcomings of the recently reported SSB-D functional. The new functionals include Grimme's D3 dispersion energy, contain a reduced number of parameters which have been optimized against a number of different interaction types. When comparing the new functionals with over thirty other density functionals, the new hybrid functional S12h and its range-separated analogue CAM-S12h are found to be the best performing ones for the different interaction types. The performance for spin states is poor for the hybrid functionals, but very well for the GGA counterpart S12g. © 2013 Elsevier B.V. All rights reserved.

Font M.,Institute Of Quimica Computacional I Catalisi Iqcc | Font M.,University of Girona | Ribas X.,Institute Of Quimica Computacional I Catalisi Iqcc | Ribas X.,University of Girona
Topics in Organometallic Chemistry | Year: 2015

Pincerlike cyclic ligands have overcome the high instability of transition metals in their higher oxidation states and have permitted the isolation of such species and the exhaustive study of their properties and reactivity. The formation and isolation of organometallic CuII and MIII (M¼Cu, Ag, Au) complexes stabilized by NCPs, carbaporphyrins, carbaporphyrinoids, heterocalixarenes, and triaza macrocyclic ligands will be discussed in this chapter. The study of these complexes have led to the discovery of unprecedented reactivity and proved the plausibility of often invoked pathways in copper-catalyzed cross-coupling reactions. Aryl-MIII (M¼Cu, Ag) stable species have been implicated as the key intermediate species that operate in coupling catalysis through two-electron redox cycles involving oxidative addition and reductive elimination fundamental steps. © Springer International Publishing Switzerland 2015

Reis H.,National Hellenic Research Foundation | Luis J.M.,Institute Of Quimica Computacional I Catalisi Iqcc | Garcia-Borras M.,Institute Of Quimica Computacional I Catalisi Iqcc | Kirtman B.,University of California at Santa Barbara
Journal of Chemical Theory and Computation | Year: 2014

Previously, a treatment of the vibrational contribution to nonlinear optical properties for molecules with large amplitude modes in a symmetric double-minimum potential well was devised. The vibronic energies were written as a power series in the field for two limiting cases of the ratio between the field-induced energy and the zero-field splitting energy of the two lowest vibronic states. This treatment is extended here to include all values of the ratio and also an asymmetric double-well potential. It is shown that a consistent treatment of NLO effects in the general case leads to new field expansion coefficients, which are formulated in terms of the usual dipole moment and (hyper)polarizabilities. As an example, the new treatment is applied to the inversion motion of CH3-. © 2013 American Chemical Society.

Prat I.,Institute Of Quimica Computacional I Catalisi Iqcc | Company A.,Institute Of Quimica Computacional I Catalisi Iqcc | Corona T.,Institute Of Quimica Computacional I Catalisi Iqcc | Parella T.,Autonomous University of Barcelona | And 2 more authors.
Inorganic Chemistry | Year: 2013

A family of iron complexes with the general formula [FeII( R,R′Pytacn)(X)2]n+ is described, where R,R′Pytacn is the tetradentate ligand 1-[(4-R′-6-R-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, R refers to the group at the α-position of the pyridine, R′ corresponds to the group at the γ-position, and X denotes CH3CN or CF3SO3. Herein, we study the influence of the pyridine substituents R and R′ on the electronic properties of the coordinated iron center by a combination of structural and spectroscopic characterization using X-ray diffraction, 1H NMR and UV-vis spectroscopies, and magnetic susceptibility measurements. The electronic properties of the substituent in the γ-position of the pyridine ring (R′) modulate the strength of the ligand field, as shown by magnetic susceptibility measurements in CD3CN solution, which provide a direct indication of the population of the magnetically active high-spin S = 2 ferrous state. Indeed, a series of complexes [FeII(H,R′Pytacn)(CD 3CN)2]2+ exist as mixtures of high-spin (S = 2) and low-spin (S = 0) complexes, and their effective magnetic moment directly correlates with the electron-releasing ability of R′. On the other hand, the substitution of the hydrogen atom in the α-position of the pyridine by a methyl, chlorine, or fluorine group favors the high-spin state. The whole family of complexes has been assayed in catalytic C-H and C=C oxidation reactions with H2O2. These catalysts exhibit excellent efficiency in the stereospecific hydroxylation of alkanes and in the oxidation of olefins. Remarkably, R′-substituents have little influence on the efficiency and chemoselectivity of the catalytic activity of the complexes, but the selectivity toward olefin cis-dihydroxylation is enhanced for complexes with R = Me, F, or Cl. Isotopic labeling studies in the epoxidation and cis-dihydroxylation reactions show that R has a definitive role in dictating the origin of the oxygen atom that is transferred in the epoxidation reaction. © 2013 American Chemical Society.

Cusso O.,Institute Of Quimica Computacional I Catalisi Iqcc | Garcia-Bosch I.,Institute Of Quimica Computacional I Catalisi Iqcc | Ribas X.,Institute Of Quimica Computacional I Catalisi Iqcc | Lloret-Fillol J.,Institute Of Quimica Computacional I Catalisi Iqcc | Costas M.,Institute Of Quimica Computacional I Catalisi Iqcc
Journal of the American Chemical Society | Year: 2013

A non-heme iron complex that catalyzes highly enantioselective epoxidation of olefins with H2O2 is described. Improvement of enantiomeric excesses is attained by the use of catalytic amounts of carboxylic acid additives. Electronic effects imposed by the ligand on the iron center are shown to synergistically cooperate with catalytic amounts of carboxylic acids in promoting efficient O-O cleavage and creating highly chemo-and enantioselective epoxidizing species which provide a broad range of epoxides in synthetically valuable yields and short reaction times. © 2013 American Chemical Society.

Canta M.,Institute Of Quimica Computacional I Catalisi Iqcc | Font D.,Institute Of Quimica Computacional I Catalisi Iqcc | Gomez L.,Institute Of Quimica Computacional I Catalisi Iqcc | Ribas X.,Institute Of Quimica Computacional I Catalisi Iqcc | Costas M.,Institute Of Quimica Computacional I Catalisi Iqcc
Advanced Synthesis and Catalysis | Year: 2014

The efficient and selective oxidation of secondary C-H sites of alkanes is achieved by using low catalyst loadings of a non-expensive, readily available iron catalyst [Fe(II)(CF3SO3)2(mcp)], {Fe-mcp, [mcp=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)cyclohexane-trans-1,2-diamine]}, and hydrogen peroxide (H2O2) as oxidant, via a simple reaction protocol. Natural products are selectively oxidized and isolated in synthetically amenable yields. The easy access to large quantities of the catalyst and the simplicity of the C-H oxidation procedure make this system a particularly convenient tool to carry out alkane C-H oxidation reactions on the preparative scale, and in short reaction times. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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