From Electron Density Flow Towards Activation: Benzene Interacting with Cu(I) and Ag(I) Sites in ZSM-5. DFT Modeling

Kozyra, Paweł; Załucka, J.; Mitoraj, Mariusz P.; Brocławik, Ewa; Dátka, Jerzy

doi:10.1007/s10562-008-9620-4

Cited by 14 publications

(34 citation statements)

References 29 publications

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“…The significance of electron transfer channels important for ligand activation, measured by corresponding NOCV eigenvalues, was related for the systems of interest to the strengthening/weakening of a given intraligand bond, evidenced by the extent of the IR red-shift for the corresponding stretching frequency. [11][12][13] The analysis conformed to the intuitive view of unsaturated hydrocarbons bound either by free Cu + or by a cationic Cu(I) site in zeolite MFI via multiple bonds according to the well-known -complexation mechanism. 15 Here, the two dominant electron transfer channels (-donation and *-backdonation) weakened the multiple bond.…”

Section: Introductionsupporting

confidence: 52%

“…2. To gain insight into electronic flows connected with the formation of the Cu(I/II)-NO bond, natural orbitals for chemical valence (NOCVs) and oneelectron density transfer channels [8][9][10][11] were calculated with our home-made program. 19 The promolecule was constructed from non-interacting T1Cu(I/II) and NO fragments.…”

Section: Computational Protocolmentioning

confidence: 99%

“…We have previously studied distinct electron density transfer channels resulting from natural orbitals for chemical valence (NOCV) analysis (described in detail elsewhere) 8-10 performed for molecules coordinated to Cu(I) systems via a C-C multiple bond (benzene, ethene, or ethyne) [11][12][13] or an oxygen lone pair (formaldehyde). 13 NOCV orbitals diagonalize differential electron density (the difference between the electron density of a complex system and superimposed densities of non-interacting fragments, here a Cu(I) site and a ligand), and thus decompose global density flow accompanying ligand bonding by the site into independent density transfer channels.…”

Section: Introductionmentioning

confidence: 99%

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Electronic propensity of Cu(II) versus Cu(I) sites in zeolites to activate NO — Spin- and orbital-resolved Cu–NO electron transfer

et al. 2013

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Electronic factors responsible for the notable decline of NO activation by Cu(II) with respect to Cu(I) sites in zeolites are investigated within spin-resolved analysis of electron transfer channels between the copper center and the substrate. The results of natural orbitals for chemical valence (NOCV) charge transfer analysis for a minimal model of Cu(II) sites in zeolite ZSM-5 ({T1Cu} + NO) are compared with those for Cu(I)-NO and referenced to an interaction of NO with bare Cu + cations. The bonding of NO, which is an open-shell and non-innocent ligand, gives rise to a noticeable nondynamical correlation in the adduct with Cu(II) (reflected in a broken-symmetry solution obtained at the density functional theory (DFT) level). Four distinct components of electron transfer between the copper and NO are identified: (i) donation of an unpaired electron from the NO ʈ * antibonding orbital to the Cu species, (ii) backdonation from copper d Ќ to the NO antibonding orbital, (iii) "covalent" donation from NO ʈ and Cu d ʈ orbitals to the bonding region, and (iv) donation from the nitrogen lone pair to Cu s,d . Large variations in channel identity and significance may be noted among studied systems and between spin manifolds: channel i is effective only in the bonding of NO with either a naked Cu + cation or Cu(II) site. Channel ii comes into prominence only for the model of the Cu(I) site: it strongly activates the NO bond by populating antibonding *, which weakens the N-O bond, in contrast to channel i depopulating the antibonding orbital and strengthening the N-O bond. Channels iii and iv, however, may contribute to the strength of the bonding between NO and copper, and are of minor importance for the activation of the NO bond. This picture perfectly matches the IR experiment: interaction with either Cu(II) sites or a naked Cu + cation imposes a comparable blue-shift of NO stretching frequency, while the frequency becomes strongly red-shifted for a Cu(I) site in ZSM-5 due to enhanced * backdonation.Résumé : Pour étudier les facteurs électroniques à l'origine de la diminution notable de l'activation de NO par les sites à Cu(II) comparativement aux sites à Cu(I) dans les zéolites, on procède à une analyse résolue en spin des mécanismes de transfert d'électrons entre le centre cuivre et le substrat. On compare les résultats de l'analyse du transfert de charge selon la théorie de la valence chimique des orbitales naturelles (VCON) pour le modèle minimal des sites à Cu(II) dans ZSM-5 ({T1Cu} + NO) à ceux obtenus pour Cu(I)-NO en prenant pour référence une interaction de NO avec les cations Cu + nus. La liaison de NO, qui est un ligand à couches ouvertes et non innocent, donne lieu à une corrélation non dynamique appréciable dans l'adduit formé avec le Cu(II) (ce que reflète la solution à symétrie brisée au niveau de la DFT). On distingue quatre composantes distinctes du transfert d'électrons entre le cuivre et NO : i) donation d'un électron non apparié de l'orbitale antiliante * de NO à l'espèce Cu, ii) rétrodonation de l'o...

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Section: Introductionsupporting

confidence: 52%

Section: Computational Protocolmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electronic propensity of Cu(II) versus Cu(I) sites in zeolites to activate NO — Spin- and orbital-resolved Cu–NO electron transfer

et al. 2013

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“…50 NOCV analysis itself has already been applied by us for the problem of benzene adsorption on copper sites in zeolites which allowed for qualitative discrimination between donation and back-donation processes and shed some light on the role of the zeolite framework. 51 Here the analysis is aided by the orbital energy decomposition scheme which helps to extract the separated information on the particular charge transfer channels and its participation in the ligand bonding energy. To address both donation/back-donation from/to hydrocarbon and the role of the framework we use two partition schemes of the entire cluster (QM) model (composed of ethene molecule adsorbed on copper cation bound by part of zeolite framework) into molecular fragments: (i) the first fragment is the ethene molecule while the second one comprises of Cu(I) bound by a framework, denoted as C 2 H 4 //Cu + -ZEO À (both fragment electroneutral) and (ii) positively charged fragment consisting of the C 2 H 4 molecule and Cu(I) ion and the negatively charged fragment being the remaining part of the zeolite cluster, denoted as C 2 H 4 -Cu + //ZEO À .…”

Section: Computational Detailsmentioning

confidence: 99%

Electronic view on ethene adsorption in Cu(i) exchanged zeolites

Rejmak

Mitoraj

Brocławik

2010

Phys. Chem. Chem. Phys.

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Ethene adsorption on isolated Cu(i) sites in two types of zeolites (faujasite and MFI) is investigated by means of the embedded cluster method. Structures, energetic stabilities and C[double bond, length as m-dash]C stretching vibrations in adsorption complexes are discussed. Furthermore, for interpretative purposes, the interaction energies are decomposed, using novel approaches based on so called natural orbitals for chemical valence. Ethene is always symmetrically bound to Cu(i) ion by both C atoms. In some cases two local minima of similar stability on the potential energy surface, differing by Cu(i) site relaxation can be found that may be simultaneously populated in equilibrium. Binding energies usually decrease with the degree of reconstruction of Cu(i) site after adsorption, however, in particular cases, a more distorted structure can be slightly more stable if favorable pi* back donation overwhelms the distortion effects. Calculated values of binding energies for Cu(i)-Y zeolite (about 80 kJ mol(-1)) agree well with microcalorimetric data. We predict that ethene binding in MFI is over two times stronger (to the best of our knowledge no experimental data are available). The C[double bond, length as m-dash]C stretching frequency is not site specific, but depends only on the type of copper connectivity to oxygen nodes. The appearance of two C[double bond, length as m-dash]C bands in IR spectra of Cu(i)-faujasite can be explained as the effect of coexistence of two types of adsorption complexes, with Cu(i) coordinated to one or two framework tetrahedrons, respectively. In Cu(i)-MFI, only one type of adsorption complex with Cu(i) ion coordinated to a single tetrahedron exists, as only a single C[double bond, length as m-dash]C band is present in IR spectra.

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“…the difference between electron density for the system and for non-interacting fragments) by natural orbitals for chemical valence (NOCV) into independent density transfer channels is useful and easy for interpretation. Such analysis has been performed for the interaction of silver and copper sites with ethene, ethyne, formaldehyde, 39 benzene, 40 and NO molecules. 41,42 In this work the attention was focused on the function of the zeolite surrounding the Cu + and Cu 2+ cations interacting with the NO molecule.…”

Section: Introductionmentioning

confidence: 99%

Spin-resolved NOCV analysis of the zeolite framework influence on the interaction of NO with Cu(i/ii) sites in zeolites

Kozyra

Piskorz

2015

Phys. Chem. Chem. Phys.

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In the present work the function of a zeolite framework in modifying the properties of copper sites has been studied. The [Al(OH)4CuNO](0/+) systems were studied by applying the analysis of the electron density flows - contributions to deformation density between two interacting fragments. The systems were divided in the following partition scheme: the first fragment, [Al(OH)4](-) (tagged T1), and the second one, [CuNO](+/2+). The analysis allowed us to elucidate the function of the zeolite fragment in modification of the cation properties towards activating the NO molecule. For both [(T1)CuNO](0/+) systems several channels showing the role of the zeolite framework have been identified. The geometry of the adducts influences either the efficiency of the channels or spin polarization. The two most important channels, zeolites-cations, influence the flow of electrons between the copper site and the antibonding NO orbitals. One channel favors the π-backdonation in the plane perpendicular to the Cu-N-O plane while the other contribution influences the π-backdonation in the C-N-O plane. The first one is found only in the system with copper(I) and it is essential for facilitating the π-backdonation and activating the NO molecule. The second channel is spin sensitive for both copper(I) and copper(II) sites. In the case of the system with copper(i) the second channel favors the π-backdonation while in the system containing copper(ii) the direction of these flows is opposite for α and β electrons.

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From Electron Density Flow Towards Activation: Benzene Interacting with Cu(I) and Ag(I) Sites in ZSM-5. DFT Modeling

Cited by 14 publications

References 29 publications

Electronic propensity of Cu(II) versus Cu(I) sites in zeolites to activate NO — Spin- and orbital-resolved Cu–NO electron transfer

Electronic propensity of Cu(II) versus Cu(I) sites in zeolites to activate NO — Spin- and orbital-resolved Cu–NO electron transfer

Electronic view on ethene adsorption in Cu(i) exchanged zeolites

Spin-resolved NOCV analysis of the zeolite framework influence on the interaction of NO with Cu(i/ii) sites in zeolites

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