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. 2023 Aug 14;62(34):13681–13691. doi: 10.1021/acs.inorgchem.3c01930

Resonant Excitation Unlocks Chemical Selectivity of Platinum Lβ Valence-to-Core X-ray Emission Spectra

Christopher J Pollock 1,*, Louise M Debefve 1
PMCID: PMC10467576  PMID: 37578150

Abstract

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Valence-to-core X-ray emission spectroscopy (VtC XES) is an emerging technique that uses hard X-rays to probe the valence electronic structure of an absorbing atom. Despite finding varied applications for light elements and first row transition metals, little work has been done on heavier elements such as second and third row transition metals. This lack of application is at least partially due to the relatively low resolution of the data at the high energies required to measure these elements, which obscures the useful chemical information that can be extracted from the lower energy, higher resolution spectra of lighter elements. Herein, we collect data on a set of platinum-containing compounds and demonstrate that the VtC XES resolution can be dramatically enhanced by exciting the platinum atom in resonance with its L3-edge white line absorption. Whereas spectra excited using standard nonresonant absorption well above the Pt L3-edge display broad, unfeatured VtC regions, resonant XES (RXES) spectra have more than twofold improved resolution and are revealed to be rich in chemical information with the ability to distinguish between even closely related species. We further demonstrate that these RXES spectra may be used to selectively probe individual components of a mixture of Pt-containing compounds, establishing this technique as a viable probe for chemically complex samples. Lastly, it is shown that the spectra are interpretable using a molecular orbital framework and may be calculated using density functional theory, thus suggesting resonant excitation as a general strategy for extracting chemically useful information from heavy element VtC spectra.

Short abstract

Resonant excitation was employed to dramatically improve the resolution of platinum valence-to-core X-ray emission spectra (VtC XES), sharpening the spectra by a factor of 2 relative to nonresonant excitation. The resulting spectra possess sufficient resolution to selectively probe individual components in a mixture of closely related species.

Introduction

Understanding the mechanisms of chemical catalysts has been a long-standing goal of chemists and materials scientists. Motivated both by the desire to understand the fundamental processes at play in these reactions and also by the hope of using that understanding to inspire rational catalyst design, an extensive toolbox of characterization methods has been developed in pursuit of these goals, with structural and spectroscopic methods yielding mechanistic insights into challenging systems under operando conditions.1−3 Understanding such catalytic processes comes from characterizing the reaction intermediates involved and tracking the critical bond-forming and -breaking events.4 Because these reactions tend to be complex—often simultaneously containing reactant, product, catalyst, intermediates, and unwanted byproducts—it is desirable and often necessary to employ methods which can selectively probe individual species.

One particularly powerful suite of spectroscopic methods employs hard X-rays (≥5 keV) as a probe, enabling techniques such as X-ray absorption (XAS) and X-ray emission spectroscopy (XES). The high energies involved with these methods result in core level electron excitation, lending these methods element selectivity; the high penetration of hard X-rays allows for diverse sample environments to be probed, including samples under in situ and operando conditions.

XAS has seen wide use for nearly every element on the periodic table and has been applied to a great variety of catalytic systems. As a probe of the unoccupied orbitals of a chemical species, XAS and its companion technique, extended X-ray absorption fine structure (EXAFS), provide detailed information about the site symmetry and electronic structure of the absorbing atom, as well as precise metrical information about its nearest neighbors. XAS has been used to elucidate the details of a wide range of catalytic reactions, including operando electrocatalysis,5−7 single site Pt catalysts,8−10 and biochemical transformations.11−13

While XAS is an undeniably powerful technique, much of the information concerning the precise geometric and electronic structure of a chemical species is contained in the occupied orbitals and is thus outside the reach of absorption methods. Fortunately, access to the occupied orbitals below the Fermi level can be provided by X-ray emission spectroscopy, a method which, like XAS, begins by generating a core hole on an absorbing atom. After that initial excitation, however, electrons from higher-lying orbitals decay to fill the core hole and in the process may emit fluorescent X-rays; in XES it is these fluorescent X-rays that are analyzed.14 Of particular importance is valence-to-core (VtC) XES, which directly probes the valence level orbitals.15−18 Since changes in bonding result in significant alterations to the energies and compositions of the occupied valence orbitals, accessing this information can be crucial for understanding catalytic processes.

For first row transition metals14,19−22 and, increasingly, for other light atoms,23−27 VtC XES has been established as a powerful, element selective tool capable of interrogating the geometric and electronic structures of an absorbing atom. For example, VtC XES of first row metal species can reveal the identity15,28,29 and number30 of ligands bound to a metal center, their protonation state,31 and even the degree of intraligand bond activation.32 As a hard X-ray technique, VtC XES is a bulk sensitive probe that is applicable to a wide variety of sample environments, rendering it an attractive tool at both synchrotron sources and X-ray free electron lasers (XFELs) for the study of operando catalytic systems.

While the application of VtC XES to first row transition metals is well established, the technique has seen much less use for heavier metals even though analogous spectra may be obtained for these elements (Figure 1). In part this is likely due to the increased spectral broadening generally present for these heavier metals due to their shorter core hole lifetimes;33 VtC spectra collected by exciting above the K-edge of Mo, for example, resulted in VtC spectra with a full-width at half-maximum resolution of ∼10 eV,34 which unfortunately obscured much of the chemical information contained in these spectra. In some cases it is possible to improve the resolution by exciting at a lower energy absorption edge—e.g., the L3-edge rather than the K-edge, a strategy recently shown to work well for Ru-containing complexes35,36—though this requires an accessible absorption edge and the lower energies involved can constrain the applicable sample environments.

Figure 1.

Figure 1

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Nonresonant Lβ XES spectrum of a third row transition metal with the major transitions labeled. All transitions are to a metal-based 2p3/2 hole and originate from the following donor orbitals: Lβ2,15 = 4d5/2; Lβ7 = 5s; Lβ7′ = 4f; Lβ5 = 5d.

Another strategy to improve spectral broadening is to employ resonant excitation, whereby the incident X-ray beam is tuned to the precise energy of an absorption feature in a so-called resonant X-ray emission spectroscopy (RXES) experiment.37−40 Such methodology has been applied to systems containing heavy metals,37,38,41−43 which has resulted in improved experimental resolution and interpretability. A recent example of this approach was provided by Chen et al.,38 who investigated the valence band of PtNi alloys using high resolution VtC RXES collected at the Pt L3-edge. These spectra showed higher resolution than previously reported data and revealed clear changes with increased Ni content of the alloys, demonstrating the ability of this technique to capture subtle electronic structure changes.

Despite the promising initial results of these aforementioned experiments, VtC XES of second and third row metals remains much less developed than its first row metal and light atom counterparts, particularly with respect to molecular species. Given the catalytic importance of such heavier metals to catalysis (Pt, Pd, Ir, Mo, etc.) we sought to apply this method to a set of Pt-containing complexes in the hope of developing the information content contained within these spectra. We have measured the VtC XES from a set of 13 Pt-containing compounds that varied in their oxidation states, geometric structures, and ligand spheres (Table 1). With nonresonant excitation well above the Pt L3-edge (12.4 keV), spectral intensity changes were observed that could be correlated with the average metal–ligand covalency of the complex, though the low resolution of the VtC spectra obscured any changes in spectral shape. In contrast, by tuning the excitation energy to the white line absorption of the Pt L3-edge—thus becoming a RXES measurement—dramatic spectral sharpening was achieved. The RXES spectra showed marked changes based on the chemistry of the complex and could clearly distinguish even closely related species. A group theoretical analysis coupled to DFT calculations provided a framework to interpret these spectra and demonstrated that the chemical information content that has been well-established for first row transition metals is retained in these heavy element VtC spectra. Lastly, we showed that the improved resolution and chemical sensitivity of RXES spectra enables one to selectively probe single species within a mixture of related compounds, paving the way for this method to be applied to chemically complex samples. Taken together, these results establish VtC XES as a viable probe of Pt catalysis and, moreover, provide a general strategy for obtaining chemically useful VtC spectra of heavy transition metals.

Table 1. Summary of the Compounds Measured in This Studya.

compound Pt oxidation state coordination environment
PtO2 4+ 6 O
PtCl4 4+ 6 Cl
Na2PtCl6 4+ 6 Cl
K2PtCl4 2+ 4 Cl
cis-PtCl2(NH3)2 2+ 2 Cl, 2 N
cis-PtCl2(PEt3)2 2+ 2 Cl, 2 P
cis-PtCl2(DMSO)2 2+ 2 Cl, 2 S
PtCl2(C10H12) 2+ 2 Cl, 4 C
PtCl2 2+ 4 Cl
PtBr2 2+ 4 Br
PtI2 2+ 4 I
Pt(PPh3)2(C2H4) 0 2 P, 2 C
Pt(tBu3P)4 0 4 P
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a

Structures of all compounds studied can be found in ref (48).

Results

Selection Rules

Before approaching the data, it is instructive to consider the expected information content of these spectra relative to that from the more commonly reported K emission VtC spectra. Both experiments are governed by the dipole selection rule: for K emission spectra in Oh symmetry, this dictates that donor orbitals must possess t1u symmetry in order to impart appreciable intensity, and thus these spectra primarily probe orbitals with metal np character.44,45 As metal np character generally is a minor component of the valence orbitals in transition metal complexes, valence → metal 1s transitions tend to be weak in K emission spectra, and weak transitions can be difficult to observe above the tails from nearby more intense metal np → 1s transitions.20 Moreover, there is no direct way to probe the metal d orbitals in Oh and other centrosymmetric point groups.46

L emission spectra, on the other hand, have significantly more allowed transitions. In Oh symmetry, the cross product of t1u × t1u yields allowed donor orbital symmetries of a1g + eg + t1g + t2g; as depicted in Figure S1, this results in numerous transitions being dipole allowed including the entirety of the d manifold. In addition to the metal-based d orbitals, both ligand ns and np dominated MOs also possess appropriate symmetries, allowing L emission spectra to simultaneously probe the metal—including oxidation state and metal–ligand covalency—and ligand electronic structures. Descending in symmetry to D4h, commonly encountered for d8 Pt(II), reveals that this ability to probe both metal and ligand orbitals (allowed final states of a1g, a2g, b1g, b2g, and eg) is retained outside of the Oh point group. Indeed, this sensitivity to both ligand and metal was recently confirmed in a study of Ru 4d-to-2p XES spectra.35

Nonresonant Spectra

To assess the potential for chemical sensitivity, nonresonant (NR) XES spectra were obtained on a variety of Pt-containing complexes by exciting the complexes at 12 400 eV, well above the Pt L3-edge at ∼11 564 eV. This energy was chosen so as to minimize the Compton scattering background, which interfered with the emission spectra when lower excitation energies were used. A summary of the compounds measured can be found in Table 1, while the resulting spectra and numerical data are shown in Figure 2 and Table S1. Perhaps as expected, the Lβ2,15 “mainlines” (4d → 2p3/2 transitions, Figure 2A) are virtually identical for all complexes, reflecting the lack of participation in bonding or electronic communication between the Pt 4d and valence orbitals. Numerical results from data fitting confirm that the Lβ2,15 energy is indistinguishable within experimental uncertainty for all compounds (Table S1). Due to this insensitivity to the chemical environment, these mainlines were used to normalize the intensities of the spectra by setting their areas to a constant value of 1000, analogously to how the Kβ1,3 peak is often used to normalize the spectra of first row metals.18

Figure 2.

Figure 2

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Overlays showing the NR mainline (A) and VtC (B) spectra for all compounds studied.

Extrapolating from observations of lighter metals,18,20,47 the VtC region would be expected to show more pronounced variations due to differences in the Pt coordination environment. While variations in the intensity of the Lβ5 peak are seen between the spectra—and two fit components are required for good fits—the low resolution (∼10 eV fwhm) reduced the VtC region to a single, broad peak for all the complexes studied (Figure 2B). While a higher energy, low intensity feature was also observed in the spectra, it appeared at an energy above the Pt L3-edge (>11 570 eV) and thus is assigned to multielectron transitions that do not directly report on the valence orbital composition. A group theoretical analysis (vide supra) suggests that the Lβ5 VtC transition probes both the Pt 5d manifold and also ligand ns and np orbitals with appreciable Pt 5d character and thus has potential to serve as a probe of both the Pt oxidation state and the ligand environment. Unfortunately, the low resolution prevents these contributions from being resolved and thus greatly complicates any attempt at detailed analysis, especially considering that, to a first approximation, the effects of Pt oxidation state and Pt–ligand covalency would be expected to influence the Lβ5 intensity in opposite directions. Caution when assessing the spectral intensities is thus warranted.

Comparing the spectra from related complexes does reveal apparent trends in intensity that correlate with the chemistry of the complex (Figure 3). The PtX2 binary halides, for example, demonstrate increasing VtC intensity for Cl < Br < I, which perhaps suggests that increasing Pt–X covalency results in increased spectral intensity. This trend is retained for PtCl2L2 molecular species (Figure 3) and can also be seen in the VtC fit areas for these compounds (Table S1). Such a sensitivity to Pt–L covalency perhaps makes sense, as increasingly covalent bonds would redistribute Pt 5d character from formally empty σ* MOs to filled, ligand-localized σ bonding orbitals that can then generate VtC intensity.

Figure 3.

Figure 3

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Overlay of PtX2 binary halides (left) and PtCl2L2 molecular species (right) which suggests that larger VtC intensity correlates with increasing Pt–L covalency.

Unfortunately, the VtC intensity is also modulated by the Pt oxidation state, with higher oxidation states generally resulting in lower VtC intensities, and thus any effect from covalency can be difficult to deconvolute from that caused by differences in oxidation state. Indeed, inspection of Figure S3 and Table S1 quickly reveals similar intensity variation within a given Pt oxidation state as between different oxidation states, thus rendering any sensitivity to covalency (or oxidation state) difficult to use in practice.

Resonant Spectra

It is evident from the NR XES data that an improvement in resolution is necessary if these spectra are to be used for detailed chemical analysis. For this reason, we explored the possibility of using resonant excitation to reduce the spectral broadening, a strategy that has been used previously to increase the resolution of XES features.37−40 By employing this methodology and collecting XES spectra with the incident energy tuned to the L3-edge white line maximum—essentially collecting a “cut” through the two-dimensional RXES plane (Figure S2)—we observed dramatic sharpening of the XES spectra, with the fwhm of the spectra decreased by roughly a factor of 2 for both the mainline and the VtC region (Figure 4). This profound increase in spectral resolution—likely deriving largely from the reduced effective core hole broadening—reveals previously obscured features and allows a much more detailed analysis as compared to that possible for the NR spectra (vide infra).

Figure 4.

Figure 4

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Overlay of NR XES and RXES spectra for Na2PtCl6 showing the spectral sharpening in the mainline (left) and VtC (right) regions.

It is possible to qualitatively interpret the resonant VtC spectra within an MO framework (Figure 5 and Figure S1). Doing so reveals the presence of all expected spectral features: a low energy, low intensity peak corresponding to the ligand ns orbitals (labeled here as Lβ5″), a higher energy peak from the ligand np + Pt 5d bonding combinations (both σ and π, labeled as Lβ5′), and lastly a highest energy feature deriving from the ligand np + Pt 5d antibonding combinations (Lβ5). This analysis immediately suggests that these spectra should possess exceptional sensitivity to the chemical environment of the Pt center and, moreover, implies that each spectral feature should report on unique chemical information. We thus employed this MO framework to analyze and rationalize the significant variations seen in the experimental RXES VtC data.

Figure 5.

Figure 5

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RXES VtC spectrum for Na2PtCl6 and the corresponding simplified valence MO diagram demonstrating the presence of every predicted transition.

Comparing the RXES VtC regions for Na2PtCl6 and K2PtCl4 demonstrates the chemical sensitivity of these spectra (Figure 6). Possessing similar ligand spheres, these compounds vary most notably in their symmetry and platinum oxidation state (Oh + 4 and D4h + 2, respectively) and the associated electronic structure changes that result from reduction of the Pt: higher energy core orbitals, less covalent Pt–Cl bonds, and greater Pt 5d electron count. As predicted by MO theory, each one of these effects is visible in the VtC spectra. Namely, the higher energy of the Pt 2p orbitals in the +2 oxidation state is reflected in the VtC intensity weighted average energy (IWAE), which shifts to lower energy by 0.9 eV (Table S2). Meanwhile, the reduction in Pt–Cl covalency is readily apparent from the redistribution of intensity from the Cl 3p-localized Lβ5′ peak to the Pt 5d-localized Lβ5 peak (∼28 units of intensity in Na2PtCl6 to nearly 40 units in K2PtCl4, Table S2). Thus, in contrast to the NR XES data, the energy and the intensity profile of the RXES data provide information about both the Pt oxidation state and the ligand environment.

Figure 6.

Figure 6

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Overlay between the RXES VtC spectra of Na2PtCl6 and K2PtCl4 revealing the sensitivity of these spectra to changes in the Pt oxidation state and electronic structure.

The ability to distinguish between closely related complexes is retained even when the Pt atoms remain in the same oxidation state. The series of PtCl2L2 complexes shown in Figure 7 all contain Pt(II) and vary only in the identity of two of their four ligands, mimicking the situation found in many catalytic processes wherein only a portion of the ligand sphere changes during a reaction cycle.

Figure 7.

Figure 7

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Overlay of several PtCl2L2 complexes that demonstrate the spectral variation even among closely related species.

For K2PtCl4 the Lβ5 and Lβ5′ features are clearly resolved, assigned above as transitions from ligand-localized np orbitals at lower energy and metal-localized Pt 5d orbitals ∼4 eV higher. Replacing two chloride ligands with NH3 ligands leads to a broadening of the Lβ5′ and a ∼ 0.4 eV red-shift in the Lβ5. Alternatively, for PtCl2(PEt3)2, the Lβ5′ is again observed to broaden, though significant intensity redistribution to higher energy is also observed. Like with PtCl2(NH3)2, the Lβ5 again shifts ∼0.4 eV lower in energy. Fitting of the spectra reveals that, despite the Pt oxidation state remaining the same for all three complexes, the intensities of the Pt 5d-derived Lβ5 peaks vary appreciably (Table S2), decreasing from 42.9 units for NH3 to 34.4 units for PEt3 coordination in accordance with increasing Pt–L covalency.

The spectral differences that are observed experimentally can be related to the large energetic variations between N 2p, P 3p, and Cl 3p orbitals and the effects that those variations have on the Pt complexes’ valence electronic structures. Replacing two of the chloride ligands in [PtCl4]2– with NH3 ligands, for instance, would be expected to split and redistribute the intensity of the Lβ5′ due to the lower energy of the N 2p orbitals (relative to Cl 3p), redirecting some Pt 5d character and thus VtC intensity to lower energy MOs. The intensity of this Pt–N-derived peak would also likely be lower than that for the corresponding Pt–Cl peak due to poorer overlap between the N 2p and Pt 5d manifolds. The opposite would be expected on replacing chloride with PEt3 ligands, which should redistribute intensity to higher VtC energies. The increase in Pt–L covalency on going from N < Cl < P would also be expected to delocalize more Pt 5d character away from the filled, metal-localized d orbitals onto the ligands, consistent with the experimentally observed intensity changes in the Lβ5. These results are encouraging for the application of Lβ VtC RXES to operando catalysis where it can be expected that a portion of the metal ligand sphere may remain unchanged during a chemical transformation.

The specific observations made for this limited series of species—and the ability to quantify them through spectral fitting—are confirmed to be general by the wider set of complexes investigated (Figure S4 and Table S2). The RXES spectra generally have a resolved Lβ5 peak resulting from Pt 5d → 2p3/2 transitions, and the intensity of this peak increases with decreasing Pt oxidation state. Indeed, unlike the NR XES spectra where the various oxidation states had significant overlap in terms of intensity, the RXES Lβ5 have distinct intensity ranges for each Pt oxidation state: 28–30 units for Pt(IV), 31–43 units for Pt(II), and 52 units for Pt(0). Beyond the Pt center, the energetics of the ligand orbitals are also reported by the RXES VtC spectra; it is universally seen that increasing the energy of the ligand np orbitals results in less separation between the Lβ5 and Lβ5′ features. It can thus be concluded with high confidence that the trends observed in this set of complexes will be generally true for platinum-containing species and, indeed, likely also for other heavy transition metals.

DFT Computations

While the general character of these VtC spectra can be predicted using simple MO theory, the application of DFT calculations allows for deeper insight into the origins of the observed transitions. Following a single particle approach that has worked well for calculating nonresonant VtC spectra of first and second row transition metals,18 ORCA was used to compute the VtC spectra for the molecular platinum complexes studied here. The PBE0 functional was chosen due to its demonstrated ability to reproduce experimentally determined geometries of Pt-containing complexes.48

Despite greatly simplifying the underlying physics, as shown in Figure 8, the calculations have an overall shape that generally agrees well with that of the experimental data. The intense Lβ5 and Lβ5′ features are both reproduced, as is the weak Lβ5″, and the orbital composition of these features matches what would be expected from MO theory (Figure 5 and Figure S5). These calculations thus allow for qualitative analysis of complex experimental spectra and for systematic chemical changes to be investigated in silico.

Figure 8.

Figure 8

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Comparison between several experimental (left) and calculated (right) VtC spectra. The calculated spectra have been broadened using a 2.5 eV Gaussian, shifted in energy by −26.4 eV, and scaled in intensity to match experiment.

While the ability of these single particle DFT calculations to qualitatively reproduce the experimental data is remarkable, they do not appear to capture several important features of the experiment. Perhaps most noteworthy is the failure of the computations to display the same overall VtC intensity variations as is observed experimentally; rather, all calculated spectra possess intensities within 5% of one another (Table S4). Moreover, the intensity ratio between some calculated features (e.g., Lβ5 and Lβ5′ for [PtCl4]2–) deviates appreciably from what is seen experimentally. Lastly, the calculated IWAE energy shifts between the various species (0.8 eV, Table S4) are smaller than that seen in the experimental data (1.4 eV, Table S2). It is possible that some of these deviations are a result of the calculations not accounting for the multistate nature of the experiment, though the computations also fail to capture the intensity differences seen in the NR XES spectra (Table S1); indeed, analysis of the Muliken orbital populations confirms that the Pt d character in the occupied orbitals hardly varies between complexes, which may reflect a failure of these DFT methods to correctly capture the subtleties of the ground state valence orbital composition. Thus, while these computations can be quite useful for the qualitative assignment of the spectral features, caution should be exercised when attempting to quantitatively compare features within and between spectra. More complex DFT/ROCIS49 and TD-DFT50 computations have been demonstrated to better capture subtleties of VtC RXES spectra, and efforts are underway to employ these methods on Pt systems.

Discussion

Valence-to-core X-ray emission spectroscopy offers a number of powerful advantages for the study of chemical catalysis: The spectra are inherently element selective and can be applied to a variety of sample environments, they directly probe the valence orbital composition, and they can be collected very rapidly for time-resolved measurements. For these advantages to be leveraged in real world systems, though, it is necessary for the spectra obtained to be able to distinguish between closely related chemical species—e.g., metal centers of identical oxidation state that vary only in the identities of a portion of their ligands—within complex matrices. VtC XES of first row transition metals can accomplish this feat,30,31 though NR XES of heavier metals has generally lacked the required spectral resolution.

Our investigation herein of 13 platinum-containing compounds by nonresonant and resonant VtC XES has demonstrated both the profound resolution enhancement available with resonant excitation and also the rich chemical information of the RXES spectra. We have shown that not only can spectra be obtained that resolve contributions from the ligand and metal orbitals but also that closely related species, varying only in a portion of their ligand sphere, can be distinguished. With this established, we sought to examine whether these RXES VtC spectra could be used to selectively probe one component in a mixture of platinum-containing species.

To assess whether RXES spectra possess this level of selectivity, we collected two-dimensional RXES planes covering the VtC region on a ∼ 1:1 molar mix of K2PtCl4 and Na2PtCl6 in an attempt to resolve the contributions from these two similar species. The RXES plane of the mixture reveals two intensity maxima that are separated by ∼1.7 eV along the incident energy axis and by ∼2.4 eV along the emitted energy axis (Figure 9). This is significant as it implies that excitation at specific incident energies can produce RXES VtC spectra with unique intensity profiles. Indeed, comparing the RXES plane of the mixture with the planes of the individual components reveals that the two maxima observed in the mixture plane correspond to distinct absorption features (in this case the white line maxima) of the two constituents; this is depicted by the dashed vertical guidelines at constant incident energy in Figure 9. This demonstrates that, by exciting the mixed sample at an energy corresponding to the absorption of one of its constituents, a VtC spectrum may be obtained that is largely selective for that component.

Figure 9.

Figure 9

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VtC RXES plane of a ∼ 1:1 molar ratio mixture of K2PtCl4 and Na2PtCl6 (top), along with planes for pure K2PtCl4 (middle) and Na2PtCl6 (bottom). Guidelines through the planes at constant incident energies corresponding to absorption maxima for K2PtCl4 (left dashed vertical line) and for Na2PtCl6 (right vertical line) demonstrate both individual components give rise to resolved features in the data of the mixture. The intense feature where incident and emitted energy are equal is the scattered beam.

While the collection of full RXES planes is ideal for spectral interpretation, such data can be time-consuming to obtain, particularly for low concentration samples. Fortunately, the collection of “cuts” through the RXES plane at constant incident energies retains the ability to selectively probe the components of the mixture. Comparison of the high energy resolution fluorescence detected (HERFD) XAS spectra for the two components reveals the optimum incident energies for selective spectra are 11 564.7 and 11 567.7 eV for K2PtCl4 and Na2PtCl6, respectively, yielding >70% selectivity for each compound (Figure 10).

Figure 10.

Figure 10

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Overlay of the normalized HERFD XAS spectra for K2PtCl4 and Na2PtCl6 (left) and the percent selectivity versus excitation energy (right) for each component.

As suggested by the full planes shown in Figure 9, collecting VtC spectra at those incident energies does in fact produce spectra that have enhanced contributions from K2PtCl4 and Na2PtCl6, respectively (Figure 11). The intensity distributions of the resulting spectra have a strong energy dependence, clearly showing that they are not a simple 50:50 mixture of the constituent components. While this type of chemical selectivity from XES spectra has been previously demonstrated at the Fe Kβ1,3 mainline,51 the results reported herein are, to our knowledge, the first leveraging the sensitivity of the VtC region to this effect.

Figure 11.

Figure 11

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RXES spectra collected on the mixed sample along with those of the pure components for excitation at 11 564.7 (left) and 11 567.7 eV (right). The area under each curve has been normalized to unity, and the traces have been vertically offset for clarity. Contribution from the scattered incident beam (highest energy peak) has not been removed so as to demonstrate that it is sufficiently removed from the VtC features to allow analysis.

This demonstration of chemical selectivity—coupled to the general sensitivity of RXES VtC spectra to the electronic structure of the metal and ligands—not only opens the door to applying VtC XES to Pt-containing species but also reveals a general methodology for probing the valence electronic structure of heavy metal catalysts via excitation at the L3-edge. Indeed, while resolution enhancement by resonant excitation does not appear to be unique to L emission spectra,39,40 in practice L-edge excitation carries the additional benefit of enhancing the signal strength relative to nonresonant excitation due to the large oscillator strength of the white line transitions; RXES spectra obtained via excitation at K pre-edge transitions, in contrast, generally suffer from low count rates due to the typically low intensity of pre-edge transitions. Such signal enhancement promises to be especially useful for time-resolved operando studies of catalysis, where strong count rates lend themselves well to the dispersive collection of spectra on the seconds to milliseconds time scale.

Conclusions

In this work we have presented both resonant and nonresonant Lβ VtC XES spectra of platinum complexes. It was shown that, while the nonresonant spectra are too broad to extract much chemical information from, resonant excitation dramatically improved the spectral resolution and enabled RXES spectra to differentiate even closely related species. By employing selective excitation, component selective emission spectra may be obtained on mixtures of chemically similar species. Moreover, the RXES data clearly establish the dramatic resolution enhancement available upon resonant excitation and suggest this as a general experimental approach for XES of heavy metals. Lastly, we have shown that RXES spectra may be interpreted within a MO framework and may be calculated with qualitative agreement to experiment using DFT methods.

Experimental Details

XES Measurements

All Pt-containing complexes were obtained commercially from Sigma-Aldrich and used as received. Samples for XES were prepared by diluting the materials with BN in a suitable ratio such that the absorbance of the sample ≈2 and grinding to a fine powder. The powders were then packed into 1 mm thick Al sample cells and sealed with 25 μm thick Kapton tape.

Resonant and nonresonant X-ray emission experiments were performed at the undulator-fed PIPOXS beamline (ID2A) at the Cornell High Energy Synchrotron Source (CHESS) under ring conditions of 100 mA at 6 GeV. The incident beam was energy selected using a cryogenically cooled Si(311) monochromator and focused to a 100 × 400 μm spot at the sample using a pair of Rh-coated KB mirrors, providing ∼4 × 1011 ph/s at the sample when unattenuated. Samples were positioned at 45° relative to the incident beam and maintained below 15 K using a displex cryostat. The fluorescence signal was energy selected using five spherically bent Si(844) analyzer crystals (R = 1 m) mounted on the DAVES spectrometer52 together with a Pilatus 100K detector. He-filled bags were used to minimize attenuation of the fluorescence signal in the XES spectrometer. For nonresonant experiments the incident energy was set to 12.4 keV in order to minimize contributions from a Compton scattering background. For resonant measurements, the energy was set to the maximum of the white line absorption as determined by an Lβ2 HERFD XAS scan of the Pt L3-edge. Acceptable dwell time was determined by doing rapid successive HERFD XANES scans on the same sample spot and monitoring for changes in the edge; if needed, the incident intensity was attenuated using graphite filters upstream of the monochromator and/or Reynolds filters upstream of the sample to prolong sample stability in the beam. Details of incident energies and dwell times used for all samples can be found in Table S3.

Nonresonant XES scans of the sample were performed over the following ranges: 11 212–11 278 eV in ∼0.5 eV steps, 11 278–11 398 eV in ∼2.0 eV steps, 11 398–11 430 eV in ∼1.0 eV steps, and 11 430–11 61 3eV in ∼0.5 eV steps. Resonant XES scans were performed similarly, though with somewhat higher point densities to better accommodate the higher resolution of these spectra: 11 212–11 278 eV in ∼0.5 eV steps, 11 278–11 398 eV in ∼2.0 eV steps, 11 398–11 440 in ∼0.8 eV steps, 11 440–11 474 eV in 0.5 eV steps, 11 474–11 509 eV in 0.3 eV steps, 11 509–11 532 eV in 0.7 eV steps, 11 532–11 586 eV in 0.2 eV steps, and 11 586–11 613 eV in 0.5 eV steps.

RXES planes and selective VtC spectra were collected under similar conditions except that the samples were prepared in 0.8 mm thick sample cells and were maintained at room temperature.

Data Processing

Data were averaged in PyMCA, and then the Lβ2,15 “mainline” spectra were spliced to the VtC spectra; VtC spectra were multiplied by a scaling factor, if needed, to join with the mainline spectra. Data fitting involved fitting a minimum number of pseudo-Voight peaks to the spectrum using BluerprintXAS 4.1.4;53 normalization was achieved by setting the area under the Lβ2,15 fit components equal to 1000. The background and scattered incident beam were subtracted from the data displayed in the main text; full unsubtracted fits can be found in the Supporting Information for nonresonant (Figure S3) and resonant (Figure S4) VtC XES spectra. All fit areas and intensity-weighted average energies can be found in Tables S1 (nonresonant data) and S2 (resonant data). RXES planes were generated using simple Python scripts and corrected for spot-dependent differences in concentration; no interpolation or smoothing was performed.

DFT Calculations

All calculations were performed using ORCA 5.0.54,55 Geometric structures of all complexes were obtained from a previous optimization study48 and were used without further refinement (xyz coordinates are included in the Supporting Information here for convenience). XES calculations were performed using the one-electron formalism (described in ref (18)) with the PBE056 functional and SARC-ZORA-TZVP57 (for Pt) and ZORA-def2-TZVP58 (for all other atoms) basis sets. Solvation was modeled using the conductor-like polarizable continuum model (CPCM)59 in an infinite dielectric. and dispersion forces were included via the Becke–Johnson damping scheme (D3BJ).60,61 Relativistics were included using ZORA.62−64 Spin–orbit coupling was included in the calculations, and the acceptor orbitals were chosen to be the 2p3/2. Spectra were plotted with an applied 2.5 eV Gaussian broadening to approximately match the experiment and were scaled such that all calculated Lβ2,15 peaks had the same intensity. Sample input files can be found in the Supporting Information. Molecular orbitals were visualized using UCSF Chimera.65

Acknowledgments

We thank Dr. Dimitrios Manganas for his helpful discussions regarding the calculation of Pt Lβ VtC spectra. This work is based on research conducted at the Center for High-Energy X-ray Sciences (CHEXS), which is supported by the National Science Foundation (BIO, ENG, and MPS Directorates) under award DMR-1829070. This work was also support by NSF-PREM: Center for Interfacial Electrochemistry of Energy Materials (CiE2M) under award DMR- 1827622.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.3c01930.

  • Representative fits for all compounds under both resonant and nonresonant excitation, tables of fit parameters for all resonant and nonresonant data, sample input file for VtC XES calculations in ORCA, all calculated VtC spectra, and numerical values for calculated spectra (PDF)

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Supplementary Material

ic3c01930_si_001.pdf (961.6KB, pdf)

References

  1. Timoshenko J.; Roldan Cuenya B. In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy. Chem. Rev. 2021, 121 (2), 882–961. 10.1021/acs.chemrev.0c00396. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Dou J.; Sun Z.; Opalade A. A.; Wang N.; Fu W.; Tao F. Operando chemistry of catalyst surfaces during catalysis. Chem. Soc. Rev. 2017, 46 (7), 2001–2027. 10.1039/C6CS00931J. [DOI] [PubMed] [Google Scholar]
  3. Chakrabarti A.; Ford M. E.; Gregory D.; Hu R.; Keturakis C. J.; Lwin S.; Tang Y.; Yang Z.; Zhu M.; Bañares M. A.; Wachs I. E. A decade+ of operando spectroscopy studies. Catal. Today 2017, 283, 27–53. 10.1016/j.cattod.2016.12.012. [DOI] [Google Scholar]
  4. Neese F. High-Level Spectroscopy, Quantum Chemistry, and Catalysis: Not just a Passing Fad. Angew. Chem., Int. Ed. 2017, 56 (37), 11003–11010. 10.1002/anie.201701163. [DOI] [PubMed] [Google Scholar]
  5. Gu J.; Hsu C.-S.; Bai L.; Chen H. M.; Hu X. Atomically dispersed Fe3+ sites catalyze efficient CO2 electroreduction to CO. Science 2019, 364 (6445), 1091–1094. 10.1126/science.aaw7515. [DOI] [PubMed] [Google Scholar]
  6. Zeng R.; Yang Y.; Feng X.; Li H.; Gibbs L. M.; DiSalvo F. J.; Abruña H. D. Nonprecious transition metal nitrides as efficient oxygen reduction electrocatalysts for alkaline fuel cells. Sci. Adv. 2022, 8 (5), eabj1584 10.1126/sciadv.abj1584. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Yang Y.; Louisia S.; Yu S.; Jin J.; Roh I.; Chen C.; Fonseca Guzman M. V.; Feijóo J.; Chen P.-C.; Wang H.; Pollock C. J.; Huang X.; Shao Y.-T.; Wang C.; Muller D. A.; Abruña H. D.; Yang P. Operando studies reveal active Cu nanograins for CO2 electroreduction. Nature 2023, 614 (7947), 262–269. 10.1038/s41586-022-05540-0. [DOI] [PubMed] [Google Scholar]
  8. Tang P.; Lee H. J.; Hurlbutt K.; Huang P.-Y.; Narayanan S.; Wang C.; Gianolio D.; Arrigo R.; Chen J.; Warner J. H.; Pasta M. Elucidating the Formation and Structural Evolution of Platinum Single-Site Catalysts for the Hydrogen Evolution Reaction. ACS Catal. 2022, 12 (5), 3173–3180. 10.1021/acscatal.1c05958. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Jiang D.; Yao Y.; Li T.; Wan G.; Pereira-Hernández X. I.; Lu Y.; Tian J.; Khivantsev K.; Engelhard M. H.; Sun C.; García-Vargas C. E.; Hoffman A. S.; Bare S. R.; Datye A. K.; Hu L.; Wang Y. Tailoring the Local Environment of Platinum in Single-Atom Pt1/CeO2 Catalysts for Robust Low-Temperature CO Oxidation. Angew. Chem., Int. Ed. 2021, 60 (50), 26054–26062. 10.1002/anie.202108585. [DOI] [PubMed] [Google Scholar]
  10. Zhou X.; Sterbinsky G. E.; Wasim E.; Chen L.; Tait S. L. Tuning Ligand-Coordinated Single Metal Atoms on TiO2 and their Dynamic Response during Hydrogenation Catalysis. ChemSusChem 2021, 14 (18), 3825–3837. 10.1002/cssc.202100208. [DOI] [PubMed] [Google Scholar]
  11. Martinie R. J.; Blaesi E. J.; Krebs C.; Bollinger J. M. Jr; Silakov A.; Pollock C. J. Evidence for a Di-μ-oxo Diamond Core in the Mn(IV)/Fe(IV) Activation Intermediate of Ribonucleotide Reductase from Chlamydia trachomatis. J. Am. Chem. Soc. 2017, 139 (5), 1950–1957. 10.1021/jacs.6b11563. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Cutsail G. E. III; Banerjee R.; Zhou A.; Que L. Jr; Lipscomb J. D.; DeBeer S. High-Resolution Extended X-ray Absorption Fine Structure Analysis Provides Evidence for a Longer Fe···Fe Distance in the Q Intermediate of Methane Monooxygenase. J. Am. Chem. Soc. 2018, 140 (48), 16807–16820. 10.1021/jacs.8b10313. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Yano J.; Kern J.; Sauer K.; Latimer M. J.; Pushkar Y.; Biesiadka J.; Loll B.; Saenger W.; Messinger J.; Zouni A.; Yachandra V. K. Where Water Is Oxidized to Dioxygen: Structure of the Photosynthetic Mn4Ca Cluster. Science 2006, 314 (5800), 821–825. 10.1126/science.1128186. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Glatzel P.; Bergmann U. High resolution 1s core hole X-ray spectroscopy in 3d transition metal complexes—electronic and structural information. Coord. Chem. Rev. 2005, 249, 65–95. 10.1016/j.ccr.2004.04.011. [DOI] [Google Scholar]
  15. Bergmann U.; Horne C. R.; Collins T. J.; Workman J. M.; Cramer S. P. Chemical dependence of interatomic X-ray transition energies and intensities - a study of Mn Kβ″ and Kβ2, 5 spectra. Chem. Phys. Lett. 1999, 302 (1–2), 119–124. 10.1016/S0009-2614(99)00095-0. [DOI] [Google Scholar]
  16. Bergmann U.; Glatzel P.; Robblee J. H.; Messinger J.; Fernandez C.; Cinco R.; Visser H.; McFarlane K.; Bellacchio E.; Pizarro S.; Sauer K.; Yachandra V. K.; Klein M. P.; Cox B. L.; Nealson K. H.; Cramer S. P. High-resolution X-ray spectroscopy of rare events: a different look at local structure and chemistry. J. Synchrotron Radiat. 2001, 8 (2), 199–203. 10.1107/S0909049500016484. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Smolentsev G.; Soldatov A. V.; Messinger J.; Merz K.; Weyhermuller T.; Bergmann U.; Pushkar Y.; Yano J.; Yachandra V. K.; Glatzel P. X-ray Emission Spectroscopy To Study Ligand Valence Orbitals in Mn Coordination Complexes. J. Am. Chem. Soc. 2009, 131 (36), 13161–13167. 10.1021/ja808526m. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Lee N.; Petrenko T.; Bergmann U.; Neese F.; DeBeer S. Probing Valence Orbital Composition with Iron K beta X-ray Emission Spectroscopy. J. Am. Chem. Soc. 2010, 132 (28), 9715–9727. 10.1021/ja101281e. [DOI] [PubMed] [Google Scholar]
  19. Pollock C. J.; DeBeer S. Insights into the Geometric and Electronic Structure of Transition Metal Centers from Valence-to-Core X-ray Emission Spectroscopy. Acc. Chem. Res. 2015, 48 (11), 2967–2975. 10.1021/acs.accounts.5b00309. [DOI] [PubMed] [Google Scholar]
  20. Beckwith M. A.; Roemelt M.; Collomb M.-N. l.; DuBoc C.; Weng T.-C.; Bergmann U.; Glatzel P.; Neese F.; DeBeer S. Manganese Kβ X-ray Emission Spectroscopy As a Probe of Metal-Ligand Interactions. Inorg. Chem. 2011, 50 (17), 8397–8409. 10.1021/ic200970t. [DOI] [PubMed] [Google Scholar]
  21. Gallo E.; Bonino F.; Swarbrick J. C.; Petrenko T.; Piovano A.; Bordiga S.; Gianolio D.; Groppo E.; Neese F.; Lamberti C.; Glatzel P. Preference towards Five-Coordination in Ti Silicalite-1 upon Molecular Adsorption. ChemPhysChem 2013, 14 (1), 79–83. 10.1002/cphc.201200893. [DOI] [PubMed] [Google Scholar]
  22. Hugenbruch S.; Shafaat H. S.; Kramer T.; Delgado-Jaime M. U.; Weber K.; Neese F.; Lubitz W.; DeBeer S. In search of metal hydrides: an X-ray absorption and emission study of [NiFe] hydrogenase model complexes. Phys. Chem. Chem. Phys. 2016, 18, 10688. 10.1039/C5CP07293J. [DOI] [PubMed] [Google Scholar]
  23. Petric M.; Bohinc R.; Bučar K.; Žitnik M.; Szlachetko J.; Kavčič M. Chemical State Analysis of Phosphorus Performed by X-ray Emission Spectroscopy. Anal. Chem. 2015, 87 (11), 5632–5639. 10.1021/acs.analchem.5b00782. [DOI] [PubMed] [Google Scholar]
  24. Mathe Z.; McCubbin Stepanic O.; Peredkov S.; DeBeer S. Phosphorus Kβ X-ray emission spectroscopy detects non-covalent interactions of phosphate biomolecules in situ. Chemical Science 2021, 12 (22), 7888–7901. 10.1039/D1SC01266E. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Holden W. M.; Jahrman E. P.; Govind N.; Seidler G. T. Probing Sulfur Chemical and Electronic Structure with Experimental Observation and Quantitative Theoretical Prediction of Kα and Valence-to-Core Kβ X-ray Emission Spectroscopy. J. Phys. Chem. A 2020, 124 (26), 5415–5434. 10.1021/acs.jpca.0c04195. [DOI] [PubMed] [Google Scholar]
  26. Petric M.; Rajh A.; Vizintin A.; Talian S. D.; Dominko R.; Kavčič M. Sulfur valence-to-core X-ray emission spectroscopy study of lithium sulfur batteries. Chem. Commun. 2021, 57 (61), 7573–7576. 10.1039/D1CC03023J. [DOI] [PubMed] [Google Scholar]
  27. Qureshi M.; Nowak S. H.; Vogt L. I.; Cotelesage J. J. H.; Dolgova N. V.; Sharifi S.; Kroll T.; Nordlund D.; Alonso-Mori R.; Weng T.-C.; Pickering I. J.; George G. N.; Sokaras D. Sulfur Kβ X-ray emission spectroscopy: comparison with sulfur K-edge X-ray absorption spectroscopy for speciation of organosulfur compounds. Phys. Chem. Chem. Phys. 2021, 23 (8), 4500–4508. 10.1039/D0CP05323F. [DOI] [PubMed] [Google Scholar]
  28. Delgado-Jaime M. U.; Dible B. R.; Chiang K. P.; Brennessel W. W.; Bergmann U.; Holland P. L.; DeBeer S. Identification of a Single Light Atom within a Multinuclear Metal Cluster Using Valence-to-Core X-ray Emission Spectroscopy. Inorg. Chem. 2011, 50 (21), 10709–10717. 10.1021/ic201173j. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Lancaster K. M.; Roemelt M.; Ettenhuber P.; Hu Y.; Ribbe M. W.; Neese F.; Bergmann U.; DeBeer S. X-ray Emission Spectroscopy Evidences a Central Carbon in the Nitrogenase Iron-Molybdenum Cofactor. Science 2011, 334 (6058), 974–977. 10.1126/science.1206445. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Stieber S. C. E.; Milsmann C.; Hoyt J. M.; Turner Z. R.; Finkelstein K. D.; Wieghardt K.; DeBeer S.; Chirik P. J. Bis(imino)pyridine Iron Dinitrogen Compounds Revisited: Differences in Electronic Structure Between Four- and Five-Coordinate Derivatives. Inorg. Chem. 2012, 51 (6), 3770–3785. 10.1021/ic202750n. [DOI] [PubMed] [Google Scholar]
  31. Lassalle-Kaiser B.; Boron T. T.; Krewald V.; Kern J.; Beckwith M. A.; Delgado-Jaime M. U.; Schroeder H.; Alonso-Mori R.; Nordlund D.; Weng T.-C.; Sokaras D.; Neese F.; Bergmann U.; Yachandra V. K.; DeBeer S.; Pecoraro V. L.; Yano J. Experimental and Computational X-ray Emission Spectroscopy as a Direct Probe of Protonation States in Oxo-Bridged MnIV Dimers Relevant to Redox-Active Metalloproteins. Inorg. Chem. 2013, 52 (22), 12915–12922. 10.1021/ic400821g. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Pollock C. J.; Grubel K.; Holland P. L.; DeBeer S. Experimentally Quantifying Small-Molecule Bond Activation Using Valence-to-Core X-ray Emission Spectroscopy. J. Am. Chem. Soc. 2013, 135 (32), 11803–11808. 10.1021/ja3116247. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Krause M. O.; Oliver J. H. Natural widths of atomic K and L levels, Kα X-ray lines and several KLL Auger lines. J. Phys. Chem. Ref. Data 1979, 8 (2), 329–338. 10.1063/1.555595. [DOI] [Google Scholar]
  34. Doonan C. J.; Zhang L.; Young C. G.; George S. J.; Deb A.; Bergmann U.; George G. N.; Cramer S. P. High-Resolution X-ray Emission Spectroscopy of Molybdenum Compounds. Inorg. Chem. 2005, 44 (8), 2579–2581. 10.1021/ic050129f. [DOI] [PubMed] [Google Scholar]
  35. Levin N.; Peredkov S.; Weyhermüller T.; Rüdiger O.; Pereira N. B.; Grötzsch D.; Kalinko A.; DeBeer S. Ruthenium 4d-to-2p X-ray Emission Spectroscopy: A Simultaneous Probe of the Metal and the Bound Ligands. Inorg. Chem. 2020, 59, 8272. 10.1021/acs.inorgchem.0c00663. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Biasin E.; Nascimento D. R.; Poulter B. I.; Abraham B.; Kunnus K.; Garcia-Esparza A. T.; Nowak S. H.; Kroll T.; Schoenlein R. W.; Alonso-Mori R.; Khalil M.; Govind N.; Sokaras D. Revealing the bonding of solvated Ru complexes with valence-to-core resonant inelastic X-ray scattering. Chemical Science 2021, 12 (10), 3713–3725. 10.1039/D0SC06227H. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Pryadchenko V. V.; Srabionyan V. V.; Avakyan L. A.; van Bokhoven J. A.; Bugaev L. A. Electronic Structure of Pt and Au Compounds Measured by X-ray Emission and X-ray Absorption Spectroscopies. J. Phys. Chem. C 2012, 116 (49), 25790–25796. 10.1021/jp3073409. [DOI] [Google Scholar]
  38. Chen J.; Finfrock Y. Z.; Wang Z.; Sham T.-K. Strain and ligand effects in Pt-Ni alloys studied by valence-to-core X-ray emission spectroscopy. Sci. Rep. 2021, 11 (1), 13698. 10.1038/s41598-021-93068-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Castillo R. G.; Hahn A. W.; Van Kuiken B. E.; Henthorn J. T.; McGale J.; DeBeer S. Probing Physical Oxidation State by Resonant X-ray Emission Spectroscopy: Applications to Iron Model Complexes and Nitrogenase. Angew. Chem., Int. Ed. 2021, 60 (18), 10112–10121. 10.1002/anie.202015669. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Hall E. R.; Pollock C. J.; Bendix J.; Collins T. J.; Glatzel P.; DeBeer S. Valence-to-Core-Detected X-ray Absorption Spectroscopy: Targeting Ligand Selectivity. J. Am. Chem. Soc. 2014, 136 (28), 10076–10084. 10.1021/ja504206y. [DOI] [PubMed] [Google Scholar]
  41. Cybulskis V. J.; Bukowski B. C.; Tseng H.-T.; Gallagher J. R.; Wu Z.; Wegener E.; Kropf A. J.; Ravel B.; Ribeiro F. H.; Greeley J.; Miller J. T. Zinc Promotion of Platinum for Catalytic Light Alkane Dehydrogenation: Insights into Geometric and Electronic Effects. ACS Catal. 2017, 7 (6), 4173–4181. 10.1021/acscatal.6b03603. [DOI] [Google Scholar]
  42. Purdy S. C.; Ghanekar P.; Mitchell G.; Kropf A. J.; Zemlyanov D. Y.; Ren Y.; Ribeiro F.; Delgass W. N.; Greeley J.; Miller J. T. Origin of Electronic Modification of Platinum in a Pt3V Alloy and Its Consequences for Propane Dehydrogenation Catalysis. ACS Appl. Energy Mater. 2020, 3 (2), 1410–1422. 10.1021/acsaem.9b01373. [DOI] [Google Scholar]
  43. Kou J.; Zhu Chen J.; Gao J.; Zhang X.; Zhu J.; Ghosh A.; Liu W.; Kropf A. J.; Zemlyanov D.; Ma R.; Guo X.; Datye A. K.; Zhang G.; Guo L.; Miller J. T. Structural and Catalytic Properties of Isolated Pt2+ Sites in Platinum Phosphide (PtP2). ACS Catal. 2021, 11 (21), 13496–13509. 10.1021/acscatal.1c03970. [DOI] [Google Scholar]
  44. Pollock C. J.; DeBeer S. Valence-to-Core X-ray Emission Spectroscopy: A Sensitive Probe of the Nature of a Bound Ligand. J. Am. Chem. Soc. 2011, 133, 5594–5601. 10.1021/ja200560z. [DOI] [PubMed] [Google Scholar]
  45. Delgado-Jaime M. U.; DeBeer S.; Bauer M. Valence-to-Core X-Ray Emission Spectroscopy of Iron-Carbonyl Complexes: Implications for the Examination of Catalytic Intermediates. Chem.—Eur. J. 2013, 19 (47), 15888–15897. 10.1002/chem.201301913. [DOI] [PubMed] [Google Scholar]
  46. Rees J. A.; Martin-Diaconescu V.; Kovacs J. A.; DeBeer S. X-ray Absorption and Emission Study of Dioxygen Activation by a Small-Molecule Manganese Complex. Inorg. Chem. 2015, 54, 6410–6422. 10.1021/acs.inorgchem.5b00699. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. MacMillan S. N.; Walroth R. C.; Perry D. M.; Morsing T. J.; Lancaster K. M. Ligand-Sensitive But Not Ligand-Diagnostic: Evaluating Cr Valence-to-Core X-ray Emission Spectroscopy as a Probe of Inner-Sphere Coordination. Inorg. Chem. 2015, 54 (1), 205–214. 10.1021/ic502152r. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. Debefve L. M.; Pollock C. J. Systematic assessment of DFT methods for geometry optimization of mononuclear platinum-containing complexes. Phys. Chem. Chem. Phys. 2021, 23 (43), 24780–24788. 10.1039/D1CP01851E. [DOI] [PubMed] [Google Scholar]
  49. Maganas D.; DeBeer S.; Neese F. A Restricted Open Configuration Interaction with Singles Method To Calculate Valence-to-Core Resonant X-ray Emission Spectra: A Case Study. Inorg. Chem. 2017, 56 (19), 11819–11836. 10.1021/acs.inorgchem.7b01810. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Nascimento D. R.; Biasin E.; Poulter B. I.; Khalil M.; Sokaras D.; Govind N. Resonant Inelastic X-ray Scattering Calculations of Transition Metal Complexes Within a Simplified Time-Dependent Density Functional Theory Framework. J. Chem. Theory Comput 2021, 17 (5), 3031–3038. 10.1021/acs.jctc.1c00144. [DOI] [PubMed] [Google Scholar]
  51. Glatzel P.; Jacquamet L.; Bergmann U.; de Groot F. M. F.; Cramer S. P. Site-selective EXAFS in mixed-valence compounds using high-resolution fluorescence detection: A study of iron in Prussian Blue. Inorg. Chem. 2002, 41 (12), 3121–3127. 10.1021/ic010709m. [DOI] [PubMed] [Google Scholar]
  52. Finkelstein K. D.; Pollock C. J.; Lyndaker A.; Krawcyk T.; Conrad J. Dual-array valence emission spectrometer (DAVES): A new approach for hard x-ray photon-in photon-out spectroscopies. AIP Conf. Proc. 2016, 1741 (1), 030009. 10.1063/1.4952832. [DOI] [Google Scholar]
  53. Delgado-Jaime M. U.; Mewis C. P.; Kennepohl P. Blueprint XAS: a Matlab-based toolbox for the fitting and analysis of XAS spectra. J. Synchrotron Radiat. 2010, 17 (1), 132–137. 10.1107/S0909049509046561. [DOI] [PubMed] [Google Scholar]
  54. Neese F. Software update: the ORCA program system, version 4.0. WIREs Comput. Mol. Sci. 2018, 8 (1), e1327 10.1002/wcms.1327. [DOI] [Google Scholar]
  55. Neese F. Software update: The ORCA program system—Version 5.0. WIREs Comput. Mol. Sci. 2022, 12, e1606 10.1002/wcms.1606. [DOI] [Google Scholar]
  56. Adamo C.; Barone V. Toward reliable density functional methods without adjustable parameters: The PBE0 model. J. Chem. Phys. 1999, 110 (13), 6158–6170. 10.1063/1.478522. [DOI] [Google Scholar]
  57. Pantazis D. A.; Chen X. Y.; Landis C. R.; Neese F. All-electron scalar relativistic basis sets for third-row transition metal atoms. J. Chem. Theory Comput 2008, 4 (6), 908–919. 10.1021/ct800047t. [DOI] [PubMed] [Google Scholar]
  58. Weigend F.; Ahlrichs R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7 (18), 3297–3305. 10.1039/b508541a. [DOI] [PubMed] [Google Scholar]
  59. Barone V.; Cossi M. Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model. J. Phys. Chem. A 1998, 102 (11), 1995–2001. 10.1021/jp9716997. [DOI] [Google Scholar]
  60. Grimme S.; Antony J.; Ehrlich S.; Krieg H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132 (15), 154104. 10.1063/1.3382344. [DOI] [PubMed] [Google Scholar]
  61. Grimme S.; Ehrlich S.; Goerigk L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 2011, 32 (7), 1456–1465. 10.1002/jcc.21759. [DOI] [PubMed] [Google Scholar]
  62. van Wüllen C. Molecular density functional calculations in the regular relativistic approximation: Method, application to coinage metal diatomics, hydrides, fluorides and chlorides, and comparison with first-order relativistic calculations. J. Chem. Phys. 1998, 109, 392. 10.1063/1.476576. [DOI] [Google Scholar]
  63. van Lenthe E.; van der Avoird A.; Wormer P. E. S. Density functional calculations of molecular hyperfine interactions in the zero order regular approximation for relativistic effects. J. Chem. Phys. 1998, 108, 4783. 10.1063/1.475889. [DOI] [Google Scholar]
  64. Lenthe E. v.; Baerends E. J.; Snijders J. G. Relativistic regular two-component Hamiltonians. J. Chem. Phys. 1993, 99 (6), 4597–4610. 10.1063/1.466059. [DOI] [Google Scholar]
  65. Pettersen E. F.; Goddard T. D.; Huang C. C.; Couch G. S.; Greenblatt D. M.; Meng E. C.; Ferrin T. E. UCSF Chimera-a visualization system for exploratory research and analysis. J. Comput. Chem. 2004, 25, 1605–1612. 10.1002/jcc.20084. [DOI] [PubMed] [Google Scholar]

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