Chemistry in solution: recent techniques and applications using soft X-ray spectroscopy

Lange, Kathrin M.; Kothe, Alexander; Aziz, Emad F.

doi:10.1039/c2cp24028a

Cited by 38 publications

(46 citation statements)

References 84 publications

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“…Only relatively recently in-vacuum methods for soft X-ray RIXS spectroscopy on liquids and solutions were developed [27][28][29][30][31] and typical count rates are low due to the small fluorescence yields and the considerable solvent absorption in the soft X-ray range. The latter is particularly important when dealing with dilute samples as typical for chemically/biologically relevant samples.…”

Section: Introductionmentioning

confidence: 99%

Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives

et al. 2016

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Abstract:The valence excited states of ferric and ferrous hexacyanide ions in aqueous solution were mapped with resonant inelastic X-ray scattering (RIXS) at the Fe L2,3-and N K-edges. Probing of both the central Fe and the ligand N atoms enabled identification of the metal-and ligand-centered excited states, as well as ligandto-metal and metal-to-ligand charge transfer excited states. Ab initio calculations utilizing the RASPT2 method was used to simulate the Fe L2,3-edge RIXS spectra and enabled quantification of the covalency of both occupied and empty orbitals of π and σ symmetry. We find that π back-donation in the ferric complex is smaller compared to the ferrous complex. This is evidenced by the relative amount of Fe 3d character in the nominally 2π CN -molecular orbital of 7% and 9% in ferric and ferrous hexacyanide, respectively. Utilizing the direct sensitivity of Fe L3-edge RIXS to the Fe 3d character in the occupied molecular orbitals we also find that the donation interactions are dominated by σ-bonding. The latter is found to be stronger in the ferric complex with a Fe 3d contribution to the nominally 5σ CN -molecular orbitals of 29% compared to 20% in the ferrous complex. These results are consistent with the notion that a higher charge at the central metal atom increases donation and decreases back-donation.

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Section: Introductionmentioning

confidence: 99%

Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives

et al. 2016

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“…They found features in the total fluorescence yield (TFY) spectra when scanning the L-edges of 3d transition metal ions and complexes in solution at high concentration that dip below the fluorescence background of the solvent. It was claimed that this could be used as a new tool to study charge transfer to solvent effects (21)(22)(23)(24). The dips where attributed, first, to ultrafast electron transfer from the metal d-orbitals to the solvent (21)(22)(23)(24) and, second, to a competition of solute and solvent fluorescence (25).…”

mentioning

confidence: 99%

“…In the context of "dark channel fluorescence yield" Aziz et al interpreted this orbital mixing as supportive for the assertion of ultrafast electron transfer from the metal d-orbitals to the solvent as deduced from the metal-ion L-edge spectra (21). This electron transfer would occur during the core-hole lifetime of core-excited state in the metal-ion: As the electron excited upon x-ray absorption would have transferred to the solvent, the corresponding fluorescence decay channel would be quenched leaving a dip in the metal-ion L-edge spectrum (21)(22)(23)(24). It was claimed that the transfer would be the more efficient and correspondingly the dip would be the deeper, the stronger the orbital overlap between the metal d-orbitals and the solvent orbitals would be.…”

mentioning

confidence: 99%

“…It was claimed that this could be used as a new tool to study charge transfer to solvent effects (21)(22)(23)(24). The dips where attributed, first, to ultrafast electron transfer from the metal d-orbitals to the solvent (21)(22)(23)(24) and, second, to a competition of solute and solvent fluorescence (25). Earlier, Näslund et al proposed strong orbital mixing between the 3d orbitals of Fe ions solvated in water based on an analysis of the O K-edge absorption spectrum of aqueous solutions (26) without making a connection to any charge transfer.…”

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confidence: 99%

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Dissecting Local Atomic and Intermolecular Interactions of Transition-Metal Ions in Solution with Selective X-ray Spectroscopy

Wernet

Kunnus

Schreck

et al. 2012

J. Phys. Chem. Lett.

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Determining covalent and charge-transfer contributions to bonding in solution has remained an experimental challenge. Here the quenching of fluorescence-decay channels as expressed in dips in the L-edge x-ray spectra of solvated 3d transition-metal ions and complexes was reported as a probe. With a full set of experimental and theoretical ab initio L-edge x-ray spectra of aqueous Cr 3+ including resonant inelastic x-ray scattering we address covalency and charge-transfer for this prototypical transition-metal ion in solution. We dissect local atomic effects from intermolecular interactions and quantify x-ray optical effects. We find no evidence for the asserted ultrafast charge-transfer to the solvent and show that the dips are readily explained by xray optical effects and local atomic state dependence of the fluorescence yield. Instead we find, besides ionic interactions, a covalent contribution to the bonding in the aqueous complex of ligand to metal charge transfer character. 3 TOC Graphic:KEYWORDS Charge transfer to solvent, dark channel fluorescence yield, inverse partial fluorescence yield, total fluorescence yield, resonant inelastic x-ray scattering, transition metal ion, aqueous solution. 4The transfer of charge from a solvated ion or molecular complex to the surrounding solvent is an elementary step in numerous reactions in nature and in technological processes. Understanding charge transfer to solvent effects in molecular systems is thus of primary importance and x-ray spectroscopy with its specificity to elemental and chemical sites promises to add a new suite of powerful tools for their investigation (1). Specifically, time-resolved x-ray spectroscopy (2-11) appears to be the most direct way of probing charge transfer initiated by a pump pulse and probed as a function of time by scanning the delay of a short x-ray probe pulse. However, such effects can proceed on the few-femtosecond time scale and it is currently very challenging to achieve a corresponding time-resolution in pump-probe x-ray spectroscopy experiments.Therefore, it has been attempted to make use of the core-hole lifetime of a few femtoseconds to study ultrafast charge transfer processes for various systems such as for adsorbates on surfaces (12-18), ice (19) and aqueous solutions (20). Using resonant soft x-ray spectroscopy a coreelectron is excited into an unoccupied state of the system and the probability for it to transfer to the surroundings during the few-femtosecond core-hole lifetime will influence the core-hole decay channels. The Auger decay signal is thus the stronger, the higher the probability for its transfer to the surrounding medium during the core-hole lifetime is (15,17,18).As core-excited states can decay via Auger-electron ejection or fluorescence, the question arises whether such ultrafast electron-transfer processes are observable in the fluorescence decay channel as well. This relates to the more general questions as to whether and how bonding and charge-transfer processes can be revealed by with x-ray sp...

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“…9,10,[19][20][21] Since binding occurs solely at the Fe site, a site (element) specific probing technique is desirable, making X-ray spectroscopy the most suitable probing tool for liquid samples. [22][23][24] X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS), with the excitation photon energy tuned to the Fe L 2,3 edge, were employed here to explore the iron 3d electronic structure of the two porphyrin molecules, in which unoccupied valence levels and 3d excitations were measured respectively. 25 The photon-in (excitation) photon-out (probing) process makes our measurements bulk sensitive, significantly reducing possible interface contributions.…”

Section: Introductionmentioning

confidence: 99%

Assistance of the Iron Porphyrin Ligands to the Binding Interaction between the Fe Center and Small Molecules in Solution

et al. 2014

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Solute-solvent electronic structure interactions of iron-porphyrin at very low concentration in dichloromethane (CH 2 Cl 2 ) liquid solution are reported. Two iron porphyrin complexes are investigated here, iron octaethylporphyrin chloride (FeOEP-Cl) and iron tetraphenylporphyrin chloride (FeTPP-Cl), using X-ray absorption and emission spectroscopy at the Fe L 2,3 edge, and spectra are interpreted with the help of density functional theory/restricted open shell configuration interaction singles (DFT/ROCIS) calculations. It is argued that the Fe center of FeOEP-Cl is more capable of binding small solvent molecules, exemplified here for Cl 2 CH 2 , than FeTPP-Cl in solution. The proposed binding mechanism is through the assistance of the dipole interaction between the porphyrin-ligand system and the solvent molecule, in a situation where the ligand structure and arrangement maximize the binding interactions. Our studies demonstrate that even small ligands, depending on their structure and arrangement, can have considerable effects on porphyrin's metal center chemistry in liquid solution.

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Chemistry in solution: recent techniques and applications using soft X-ray spectroscopy

Cited by 38 publications

References 84 publications

Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives

Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives

Dissecting Local Atomic and Intermolecular Interactions of Transition-Metal Ions in Solution with Selective X-ray Spectroscopy

Assistance of the Iron Porphyrin Ligands to the Binding Interaction between the Fe Center and Small Molecules in Solution

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