Spectroscopic and magnetic studies of the 3d metallocenes

Gordon, Kevin R.; Warren, Keith D.

doi:10.1021/ic50182a038

Cited by 86 publications

(63 citation statements)

References 31 publications

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“…5.7a, gray curve) is characterized by three main components centered around 21,000, 30,000 (responsible for the color), and 43,000 cm −1 (henceforth labeled as components I, II, and III, respectively). These bands are very similar to those observed in the spectrum of chromocene in solution [85,86]. A simplified scheme of the electronic structure of Cp 2 Cr is reported in Figure 5.7b.…”

Section: Determination Of the Electronic Structure Of Cp 2 Cr By Combsupporting

confidence: 77%

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

Borfecchia¹,

Agostini²,

Bordiga³

et al. 2013

Inorganic Micro- And Nanomaterials

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Starting from the late seventies, the progressively increased availability of synchrotron light sources has allowed the execution of experiments requiring a high X-ray flux in a continuous interval [1][2][3][4]. Among the various techniques developed, X-ray absorption spectroscopy (XAS, also known as X-ray absorption fine-structure, XAFS) [5][6][7][8][9][10][11][12][13] in both near (XANES) and post (EXAFS) edge regions, has become a powerful characterization technique widely employed in many research fields concerning inorganic chemistry, such as catalysis [13][14][15][16][17], organometallic and coordination complexes [18], metal nanoparticles [19, 20], electrochemical processes [21, 22], coordination polymers or metallorganic frameworks [23], bio-inorganic molecules including metalloproteins [24-27], chemistry of actinide elements [28], and solid state chemistry [12,[29][30][31].In this chapter, we will provide a brief introduction to the basic theory of XAS spectroscopy (Section 5.2), followed by selected examples having some didactic perspective (Sections 5.3-5.7). For the sake of brevity, only a fraction of the subjects mentioned above will be discussed; in particular, the chapter will deal with: the reactivity of the CuCl 2 /Al 2 O 3 -based catalysts for ethylene oxychlorination (Section 5.3); the structure, the electronic configuration and the reactivity of Cp 2 Cr molecules encapsulated in porous solids (Section 5.4); the structural characterization of metal complexes in solution (Section 5.5); the structural characterization of the UiO-66 and UiO-67 class of metallorganic frameworks (Section 5.6); and the determination of the local structure of an Alxw Gayw In 1−xw−yw As/Al xb Ga yb In 1−xb −yb As strained heterostructure grown on InP by metallorganic vapor phase epitaxy (Section 5.7) as an example of space-resolved EXAFS applied to a topic pertinent to solid state chemistry. XAS spectroscopy: Basic backgroundThe aim of this section is to provide the reader with a concise review of the basic physical principles on which the interpretation of EXAFS and XANES data is based. For a more detailed description of the theoretical background and the experimental aspects of XAS we refer to the extensive specialized literature (e.g., [5][6][7][8][9][10][11][12][13]).

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Section: Determination Of the Electronic Structure Of Cp 2 Cr By Combsupporting

confidence: 77%

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

Borfecchia¹,

Agostini²,

Bordiga³

et al. 2013

Inorganic Micro- And Nanomaterials

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“…4 and their band energies and intensities are summarized in Table 1. The UV-visible spectrum of Ni(Ind), shows an intense, broad absorption band in the green spectral region with its maximum at 20 200 cm-' and a molar absorptivity of 3180 M-' cm-', very different from nickelocene whose lowest-energy absorption band is in the red spectral region with a first maximum at 14 500 cm-I and a much lower molar absorptivity of 60 M-' cm-I (23)(24)(25). The band maximum of Ni(Ind), is higher in energy by 5700 cm-' and more intense by almost two orders of magnitude than in nickelocene.…”

Section: Resultsmentioning

confidence: 94%

Absorption spectroscopy of (Ind)Ni(PPh₃)X (Ind = indenyl, 1-Me-indenyl; X = Cl, Br, Me) and M(Ind)₂ (M = Ni, Ru; Ind = indenyl)

Bayrakdarian¹,

Davis²,

Reber³

et al. 1996

Can. J. Chem.

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Abstract:The electronic structures of two types of transition metal indenyl complexes have been studied. The first type, a series of (Ind)Ni(PPh,)X compounds (Ind = indenyl, 1-Me-indenyl; X = C1, Br, Me) was investigated by absorption spectroscopy and Extended Huckel Molecular Orbital calculations. The energy differences between calculated levels are in good agreement with experimental band positions. For example, the lowest energy singlet-singlet band maximum for (Ind)Ni(PPh,)Cl is at 19 500 cm-I and the calculated HOMO-LUMO difference is 19 817 cm-I. For X = Me, the calculated energy difference increases to 21 930 cm-I and the corresponding absorption band is at 22 500 cm-I. The influence of the metal-ligand interactions on the molecular orbitals is discussed. The second category of indenyk'the bis(indeny1) compounds of Ni and Ru, show absorption spectra that are markedly different from those of nickelocene and ruthenocene. For example, in comparison to nickelocene, the first absorption band of Ni(Ind), is 5700 cm-' higher in energy and is more intense by two orders of magnitude; in contrast, the first absorption maximum of Ru(Ind)? is 6600 cm-' lower in energy than observed for ruthenocene. The characteristics and relaxation dynamics of the lowest energy excited states are discussed.Key words: absorption spectroscopy, indenyl, nickel, ruthenium, EHMO analysis.

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“…52 The transition of one of the 16 valence electrons into a nonoccupied molecular orbital is responsible for the observed optical spectrum. Only the lowest frequency component (21000 cm Conversely, the assignment of the 30000 and 43000 cm -1 bands in terms of a crystal field is less straightforward.…”

Section: Electronic Properties Of Hosted Cp 2 Cr: Uv-vis and Xanes Rementioning

confidence: 99%

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

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Chromocene (Cp 2 Cr) hosted inside the supercage cavities of a NaY zeolite undergoes a structural distortion induced by the strong local electric fields generated by charge-balancing counterions. This effect, clearly observed by an in situ Cr K-edge extended X-ray absorption fine structure (EXAFS) study, is the key factor in enhancing the reactivity of Cp 2 Cr toward CO. The Cp 2 Cr(CO) adducts initially formed are not as stable as when hosted in nonpolar environments such as toluene solution or polystyrene. The presence of strong anionic/ cationic pairs (Y -/Na + ) favors, in a CO atmosphere, the loss of a Cp ring driven by an electron transfer mechanism (accompanied by ligand rearrangement) that results in the formation of the charged [CpCr(CO) 3 ] - and [Cp 2 Cr(CO)]+ carbonyl species that are stabilized by Na + and Y -pairs. Shape selectivity of the supercage cavity of the Y zeolite is necessary for this reaction, as it can host the two Cp 2 Cr molecules needed for disproportionation. Fast Fourier transform infrared (FTIR) spectroscopy, working in operando conditions, allows us to follow the time evolution of the IR stretching modes peculiar of reactants and products and thus to infer a reaction mechanism. The combination of quantum mechanical calculation with an in situ EXAFS study supports the hypothesis made on the basis of IR results. The work is further demonstration that zeolitic voids act as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis. In this context, the investigation of metallocene reactivity inside a polar matrix can be extremely useful to understanding their properties in polymerization conditions, where they are usually found as part of an ion pair, together with the anionic form of the activator (e.g., MAO).

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Spectroscopic and magnetic studies of the 3d metallocenes

Cited by 86 publications

References 31 publications

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

Absorption spectroscopy of (Ind)Ni(PPh₃)X (Ind = indenyl, 1-Me-indenyl; X = Cl, Br, Me) and M(Ind)₂ (M = Ni, Ru; Ind = indenyl)

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

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Spectroscopic and magnetic studies of the 3d metallocenes

Cited by 86 publications

References 31 publications

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

Absorption spectroscopy of (Ind)Ni(PPh3)X (Ind = indenyl, 1-Me-indenyl; X = Cl, Br, Me) and M(Ind)2 (M = Ni, Ru; Ind = indenyl)

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

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Absorption spectroscopy of (Ind)Ni(PPh₃)X (Ind = indenyl, 1-Me-indenyl; X = Cl, Br, Me) and M(Ind)₂ (M = Ni, Ru; Ind = indenyl)