L-edge X-ray Absorption Spectra Research Articles

The trials and triumphs of modelling X-ray absorption spectra of transition metal phthalocyanines.

This study explores the electronic structure of Co, Fe and Mn phthalocyanines (TMPcs) as well as their perfluorinated counterparts through a series of electronic structure calculations utilizing multireference methods and by simulating their metal L-edge and ligand (nitrogen and fluorine) K-edge X-ray absorption spectra (XAS) in an angle-resolved manner. Simulations targeting different ground-state symmetries, where relevant, have been conducted to observe changes in the N K-edge lineshape. The applicability of the quasi-degenerate formulation of n-electron valence state perturbation theory (QD-NEVPT2) for L-edge X-ray absorption spectroscopy (XAS) is evaluated, alongside the use of a restricted active space (RAS) formalism to describe the final-state multiplets generated by L-shell X-ray processes. Our findings provide valuable insights into the electronic properties of TMPcs, in particular with respect to the effect of fluorination, and demonstrate the broad applicability of various formulations of NEVPT2 in spectral simulations. Moreover, this study highlights the utility of manual truncation of the configuration spaces in order to allow for large active orbital spaces in aforementioned calculations.

Interpreting the Cu-O2 Antibonding Nature in Two Cu-O2 Complexes from Cu L-Edge X-ray Absorption Spectra.

Cu-O2 structures play important roles in bioinorganic chemistry and enzyme catalysis, where the bonding between the Cu and O2 parts serves as a fundamental research concern. Here, we performed a multiconfigurational study on the copper L2,3-edge X-ray absorption spectra (XAS) of two copper enzyme model complexes to gain a better understanding of the antibonding nature from the clearly interpreted structure-spectroscopy relation. We obtained spectra in good agreement with the experiments by using the restricted active space second-order perturbation theory (RASPT2) method, which facilitated reliable chemical analysis. Spectral feature interpretations were supported by computing the spin-orbit natural transition orbitals. All major features were assigned to be mainly from Cu 2p to antibonding orbitals between Cu 3d and O2 π*, Cu 3d-πO-O* (type A), and a few also to mixed antibonding/bonding orbitals between Cu 3d and O2 π, Cu 3d ± πO-O (type M). Our calculations provided a clear illustration of the interactions between Cu 3d and O2 π*/π orbitals that are carried in the metal L-edge XAS.

Ultraviolet-C persistent luminescence and defect properties in Ca2Al2SiO7:Pr3+

In recent years, significant attention has been focused on the study of materials with ultraviolet (UV) persistent luminescence (PersL) due to their prospective application possibilities. Although novel UV persistent phosphors are being developed, reports on defect properties and PersL mechanisms are limited. In this study, the incorporation of Pr3+ ions in Ca2Al2SiO7 is analyzed using X-ray diffraction (XRD) and X-ray absorption techniques, whereas PersL properties are characterized by photoluminescence (PL), thermostimulated luminescence (TSL) and electron paramagnetic resonance (EPR) methods. Analysis of the Pr L3-edge X-ray absorption spectra suggests that praseodymium atoms substitute for calcium atoms. The UV-C PersL of the host results from thermally assisted recombination of charge carriers with trap depths within the 0.50–0.87 eV range. Moreover, a partial correlation of PersL and TSL with the decay of X-ray-induced paramagnetic centers was observed. This study expands the knowledge base on the structure of Ca2Al2SiO7 and establishes the optimal Pr3+ concentration for efficient UV-C PersL.

Metal monovacancy-induced spin polarization for simultaneous energy recovery and wastewater purification

Simultaneous hydrogen generation and pollutants removal is considered as the potential solution to the energy and environmental crisis, which can cut the consumption of expensive sacrificial electron donors and reduce the ecotoxicity of wastewater containing pollutants. However, the integration of two redox half-reactions in one system is still a challenge, limited by irreconcilable reaction conditions and low kinetics. In this study, ZnO with abundant metal monovacancies (Zn-V-m) was fabricated to manipulate the spin state by tailoring the electron occupancy of eg-orbitals, which simultaneously endowed the material with both outstanding photocatalytic oxidation and reduction performance. Compared with pristine ZnO, the prepared Zn-V-20 increases the H2 production rate by 56.4-fold and enhances the pollutants removal efficiency by 27.5-fold. It is impressive that simultaneous hydrogen generation and pollutants degradation in one system is accomplished and accelerated. Furthermore, Zn L-edge X-ray absorption spectra (XAS) and density functional theory (DFT) calculations suggest that low electron occupancy of eg-orbitals optimizes the spin structure and leads to spin polarization, which provides the critical motivation for enhancing photocatalytic performance. This work accelerates the reaction rates of pollutants degradation and hydrogen generation at the surface interface by manipulating electron spin polarization, guiding the rational design of TMO-based catalysts for simultaneous energy recovery and wastewater purification.

Ni, Co, and Mn L3-edge X-ray absorption micro-spectroscopic study on LixNi0.88Co0.08Mn0.04O2 primary particles upon annealing from room temperature to 800 °C

LixNi0.88Co0.08Mn0.04O2 primary particles for lithium ion battery (LIB) applications were annealed in situ from room temperature (RT) to 200, 400, 600, and 800 °C. At each of these temperatures, space-resolved Ni L3-, Co L3-, and Mn L3-edge X-ray absorption spectra of the particles were acquired with 30 nm focused X-rays by using synchrotron-based scanning transmission X-ray microscopy (STXM). This study aimed to investigate the changes induced by the annealing temperature in the local oxidation number, phase, and microscale shape within the particles. At RT, the average oxidation numbers of the Ni, Co, and Mn ions were +3, +3, and +4, respectively. At 200 °C, the average oxidation numbers of the Co and Mn ions were basically the same as those at RT, and those of the Ni ions were between +2 and +3. At 400 °C, the average oxidation numbers of the Ni and Co ions decreased to +2, whereas that of the Mn ions was +4. The average oxidation number of the Ni ions was noticeably lower for smaller particles and on the edges of the particles. At 600 °C, the Ni and Co ions were mostly in the metallic state, the Mn ions were reduced to an oxidation number of +2, and the distribution of Mn ions differed from that of the Ni and Co ions. At 800 °C, the Ni and Co ions were mostly in the metallic state, and the oxidation number of the Mn ions was predominantly +2. At this temperature, strong changes in density distributions of the Mn, Ni, and Co ions occurred.

Functionalized polyarylether-based COFs for rapid and selective extraction of uranium from aqueous solution

Selective uranium extraction from aqueous solution is critical for both radioactive contamination remediation and uranium recovery from seawater. Herein, amidoxime (−AO) and carboxyl (–COOH) groups are equipped on a polyarylether-based covalent organic framework (COF) for fabrication of post-modified adsorbents, JUC-505-AO and JUC-505-COOH. The maximum adsorption capacities (Qm) of JUC-505-AO and JUC-505-COOH are 395 mg⋅g−1 and 464 mg⋅g−1, respectively. JUC-505-COOH shows preponderant uranium extraction efficiencies of 36–95% at low pH 2–4, and its removal performances are almost unaffected at high temperature ranging from 25 to 80 °C. Whereas, JUC-505-AO exhibits an impressive adsorption kinetics with the adsorption process equilibrates within 20 min (C0 = 20 mg⋅L-1), and marked sorption selectivity toward uranium against coexisting metal ions. JUC-505-AO also capable of extracting uranium with fast kinetics and capacity (Qm = 4604 μg⋅g−1) from real seawater. U L3 edge X-ray absorption spectra analysis reveals that uranyl ions in JUC-505-AO are anchored by coordinating with O and N from the oxime groups by η2 mode with the coordination numbers of 5 or 6. Meanwhile, HOH⋅⋅⋅O hydrogen bonds between the coordinated water of the hydrated uranyl ions and the oxygen atoms on the skeleton of JUC-505-AO were observed by density functional theory simulations.

Two-Component Multireference Restricted Active Space Configuration Interaction for the Computation of L-Edge X-ray Absorption Spectra.

X-ray absorption spectroscopy is a powerful probe of local electronic and nuclear structures, providing insights into chemical processes. The theoretical prediction and interpretation of metal L-edge X-ray absorption spectra are complicated by both relativistic effects, including spin-orbit coupling and the multiconfigurational nature of the states involved. This work details an exact two-component multireference restricted active space (RAS) configuration interaction scheme that uses an exact two-component state-averaged complete active space self-consistent-field method, which includes the spin-orbit coupling in a variational manner, for the accurate description of the electronic structure before using a RAS configuration interaction method to describe the core excited states of the X-ray spectrum. Benchmark calculations are presented for a series of iron-containing complexes, with results showing key features of the spectrum being reproduced, including ligand-to-metal charge transfer and shake-up excitations.

Determining electronic properties from L -edge x-ray absorption spectra of transition metal compounds with artificial neural networks

X-ray absorption spectroscopy at the L-edge probes transitions of 2p-electrons into unoccupied d-states. Applied to transition metal atoms, this experimental technique can provide valuable information about the electronic structure of d-states. However, multiplet effects, spin-orbit coupling, a large number of possible transitions can cause a rather involved nature of 2p XAS spectra, which can often complicate extracting of information directly from them. Here, artificial neural networks trained on simulated spectra of a 2p XAS model Hamiltonian are presented that can directly determine information about atomic properties and the electronic configuration of d-states from L-edge X-ray absorption spectra. Moreover, the adaptable nature of artificial neural networks (ANNs) allows extending their capability to obtain information about the electronic ground state and core hole lifetimes from 2p XAS spectra as well as to incorporate external factors, such as temperature and experimental convolution that can affect details in spectral features. The effects of noise and background contributions in spectra on the accuracy of ANNs are discussed and the method is validated on experimental spectra of transition metal compounds, including metal-organic molecules and metal oxides.

X-ray absorption investigation of the site occupancies of the copper element in nominal Cu3Zn(OH)6FBr* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11934017 and 11774399), the Key Research and Development Program of China (Grant No. 2016YFA0401000), the Chinese Academy of Sciences (Grant No. 112111KYSB20170059), and the K. C. Wong Education Foundation (Grant No. GJTD-2018-01).

With Zn substitution to the three-dimensional antiferromagnetically ordered barlowite Cu4(OH)6FBr, Cu3Zn(OH)6FBr shows no magnetic phase transition down to 50 mK, and the system is suggested to be a two-dimensional kagomé quantum spin liquid [Chin. Phys. Lett. 34 077502 (2017)]. A key issue to identify such phase diagram is the exact chemical formula of the substituted compound. With Cu L-edge x-ray absorption spectrum (XAS) combined with the MultiX XAS calculations, we evaluate the Cu concentration in a nominal Cu3Zn(OH)6FBr sample. Our results show that although the Cu concentration is 2.80, close to the expected value, there is 34% residual Cu occupation in intersite layers between kagomé layers. Thus the Zn substitution of the intersite layers is not complete, and likely it intrudes the kagomé layers.

Ab initio methods for L-edge x-ray absorption spectroscopy

The theoretical prediction of x-ray absorption spectra (XAS) has become commonplace in electronic structure theory. The ability to better model and understand L-edge spectra is of great interest in the study of transition metal complexes and a wide variety of solid state materials. However, until recently few first-principles works have modeled L-edge XAS due to the presence of strong spin–orbit coupling in the 2p orbitals, which splits the observed peaks into multiple groups of features. Therefore, a proper description of spin–orbit coupling is vital for the successful prediction of L-edge spectra. A number of new approaches that incorporate spin–orbit coupling have recently made advances in the computation of L-edge spectra. In this review, we describe recent work in computational L-edge XAS and how these methods may continue to improve in the future. Comparison of the advantages and disadvantages of the various approaches are considered, with special attention to not only the computational cost of the level of theory but also the various approaches that can be used to compute the absorption spectra with a large number of high energy excited states.

Development of fluorescence-yield wavelength-dispersive x-ray absorption spectroscopy in the soft x-ray region for time-resolved experiments.

A fluorescence-yield wavelength-dispersive x-ray absorption spectroscopy technique in the soft x-ray region, by which the x-ray absorption spectra are recorded without scanning the monochromator, has been developed. The wavelength-dispersed soft x rays, in which the wavelength (photon energy) continuously changes as a function of the position, illuminate the sample, and the emitted fluorescence soft x rays at each position are separately focused by an imaging optics onto each position at a soft x-ray detector. Ni L-edge x-ray absorption spectra for Ni and NiO thin films taken in the wavelength-dispersive mode are shown in order to demonstrate the validity of the technique. The development of the technique paves the way for a real-time observation of time-dependent processes, such as surface chemical reactions, with much higher gas pressure compared to the electron-yield mode, as well as under magnetic and electric fields.

Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material.

Layered Li-rich Ni, Mn, Co (NMC) oxide cathodes in Li-ion batteries provide high specific capacities (>250 mAh/g) via O-redox at high voltages. However, associated high-voltage interfacial degradation processes require strategies for effective electrode surface passivation. Here, we show that an acidic surface treatment of a Li-rich NMC layered oxide cathode material leads to a substantial suppression of CO2 and O2 evolution, ∼90% and ∼100% respectively, during the first charge up to 4.8 V vs Li+/0. CO2 suppression is related to Li2CO3 removal as well as effective surface passivation against electrolyte degradation. This treatment does not result in any loss of discharge capacity and provides superior long-term cycling and rate performance in comparison to as-received, untreated materials. We also quantify the extent of lattice oxygen participation in charge compensation ("O-redox") during Li+ removal by a novel ex situ acid titration. Our results indicate that the peroxo-like species resulting from O-redox originate on the surface at least 300 mV earlier than the activation plateau region at around 4.5 V. X-ray photoelectron spectra and Mn L-edge X-ray absorption spectra of the cathode powders reveal a Li+ deficiency and a partial reduction of Mn ions on the surface of the acid-treated material. More interestingly, although the irreversible oxygen evolution is greatly suppressed through the surface treatment, O K-edge resonant inelastic X-ray scattering shows that the lattice O-redox behavior is largely sustained. The acidic treatment, therefore, only optimizes the surface of the Li-rich material and almost eliminates the irreversible gas evolution, leading to improved cycling and rate performance. This work therefore presents a simple yet effective approach to passivate cathode surfaces against interfacial instabilities during high-voltage battery operation.

Enhancement of local piezoresponse in samarium and manganese co-doped bismuth ferrite ceramics

Field-induced polarization switching and electromechanical mechanisms in lead-free multiferroic BiFeO3 materials are essential for applications in nanoscale logic and magnetoelectric-controlled devices. This work highlights enhanced ferroelectric polarization switching and electromechanical strain behaviors in (Sm, Mn) co-doped (Bi0.95Sm0.05)(Fe1-xMnx)O3 ceramics with increasing Mn substitution. The Mn L-edge and oxygen K-edge synchrotron X-ray absorption spectra confirm a Mn3+→Mn4+ valence shift and reduced O 2p–Fe 3d and O 2p–Bi 6sp orbital hybridizations in the Mn-doped specimens. High-resolution transmission electron microscopy (TEM) confirms larger polar nano-regions (PNRs) and oxygen octahedral tilt in the Mn-doped specimens. Out-of-plane piezoresponse force microscopy (OP-PFM) shows improved local ferroelectric polarization and electromechanical response within grains by the Mn substitution. The enhanced ferroelectricity and piezoelectricity may originate from collective effects, including fewer oxygen vacancies, reduced covalent bonding, larger oxygen octahedral tilt and PNRs, caused by the Sm and Mn co-substitution.

Probing and Tuning Lattice Oxygen Redox in Li2RuxM(1-x)O3 for Design of High-Energy Li-Ion Batteries

The participation of anion redox in lithium transition metal oxides such as Li2RuO3 and Li2MnO3 for positive electrodes have opened a new avenue to boost up the energy density of current lithium-ion batteries. There are many schools of thoughts for the physical origin proposed to be responsible for anion redox and more direct and clear experimental evidence of anion redox is needed to further understand and utilize this phenomena. In the first part of this work, we demonstrated the electronic signature of oxygen-oxygen coupling, direct evidence central to lattice oxygen redox (O2-/(O2)n-) in charged Li2-xRuO3 after Ru oxidation (Ru4+/Ru5+) upon first-electron removal with lithium de-intercalation. Experimental and simulated Ru L3-edge X-ray absorption spectra (XAS) revealed that the increase in the high-energy shoulder intensity upon lithium de-intercalation resulted from increased O-O coupling, inducing (O-O) σ* with π overlap with Ru d-manifolds, in agreement with the similar changes in the O K-edge XAS spectra. Further support came from experimental and simulated O K-edge X-ray emission spectra (XES), where the broadening of the oxygen nonbonding feature upon charging also originated from creation of (O-O) σ* states. By combining differential electrochemistry mass spectrometry (DEMS) with core-level spectroscopies, we are able to quantify the percentage of this lattice oxygen redox across different Li2RuxM(1-x)O3 (M=Ti, Cr, Mn, Fe, Ir, Sn) chemistries, through which we proposed a preliminary electronic descriptor for reversible bulk oxygen redox activity. This study constructed a transferrable framework to rationally interpret the spectroscopic features by combining experiments and theory, and pinpointed the key spectra footprints related to lattice oxygen redox from a molecular level. We also proposed a simple descriptor to rationalize and facilitate novel positive electrode materials design for reversible anion redox activities in high-energy Li-ion batteries.

Modeling L2,3-edge X-ray absorption spectroscopy with linear response exact two-component relativistic time-dependent density functional theory.

X-ray absorption spectroscopy (XAS) is a powerful tool that can provide physical insights into element-specific chemical processes and reactivities. Although relativistic time-dependent density functional theory (TDDFT) has been previously applied to model the L-edge region in XAS, there has not been a more comprehensive study of the choices of basis sets and density functional kernels available for variational relativistic excited state methods. In this work, we introduce the implementation of the generalized preconditioned locally harmonic residual algorithm to solve the complex-valued relativistic TDDFT for modeling the L-edge X-ray absorption spectra. We investigate the L2,3-edge spectra of a series of molecular complexes using relativistic linear response TDDFT with a hybrid iterative diagonalization algorithm. A systematic error analysis was carried out with a focus on the energetics, intensities, and magnitude of L2-L3 splitting compared to experiments. Additionally, the results from relativistic TDDFT calculations are compared to those computed using other theoretical methods, and the multideterminantal effects on the L-edge XAS were investigated.

Mechanism of Gd3+ uptake in gypsum (CaSO4·2H2O): Implications for EPR dating, REE recovery and REE behavior

Rare earth elements (REE) in gypsum have long attracted interest for geochemical applications from the reconstruction of paleoclimate, paleoenvironment and paleohydrology to the monitoring of volcanic and seismic activities. Resurgent interests in REE in gypsum stem from the potential recovery of these high-tech metals from gypsum-rich tailings. Development of new geochemical applications and invention of effective recovery technologies all require knowledge about the mechanism of REE uptake in gypsum. In this contribution, we have investigated Gd-doped gypsum from the gel diffusion technique at ambient conditions in the pH range from 6.5 to 9.5. Inductively coupled plasma mass spectrometry analyses of Gd-doped gypsum yielded 752 ppm Gd at pH = 6.5 down to 2.8 ppm Gd at pH = 9.5. Synchrotron Gd L3-edge X-ray absorption spectra show that Gd3+ has a local environment similar to that of Ca2+ in gypsum. Single-crystal electron paramagnetic resonance (EPR, also known as electron spin resonance or ESR) spectra reveal a dominant Gd3+ center with weak satellites. The dominant Gd3+ center arises from a substitutional Gd3+ ion at the Ca site retaining its C2 local symmetry, which is also confirmed by pulsed electron nuclear double resonance (ENDOR) data for proton hyperfine structures up to 5.2 Å away from Gd3+. The satellites are attributable to a Gd3+-Gd3+ pair (dimer) along the crystallographic a-axis with a dipolar coupling constant Dd/geβe = −13 G, which corresponds to a distance of 12.6 Å between the two Gd3+ ions and provides the first experimental confirmation for the substitution 2Gd3+ + □ = 3Ca2+ in gypsum. Hole trapping at cation vacancies associated with the incorporation of Gd3+ (and other trivalent REE) in gypsum offers a new class of radiation-induced paramagnetic defects in this mineral for EPR/ESR dating. These results also have implications for developing new technologies for effective recovery of REE from gypsum-rich tailings and for understanding the behavior of REE in evaporites and aqueous solutions.

Restricted Open-Shell Configuration Interaction Singles Study on M- and L-edge X-ray Absorption Spectroscopy of Solid Chemical Systems.

In this study the M- and L-edge X-ray absorption spectra of a series of open- and closed-shell solids (TiO2 rutile, α-Fe2O3 hematite, FeS2 pyrite, and the spinel Co3O4) are investigated with the restricted open-shell configuration interaction singles methods (ROCIS/DFT and PNO-ROCIS/DFT) using the embedded cluster approach. ROCIS/DFT type of methods are grounded in wave function-based ab initio electronic structure theory and have shown great performance in the field of X-ray spectroscopy in particular in the field of transition metal L-edge spectroscopy. In this work we show that ROCIS/DFT can be used to calculate and interpret metal M- and L-edge XAS spectra of solids. To this end, clusters with up to 52 metal centers are considered. In all cases good to excellent agreement between theory and experiment is obtained. The experimentally probed local coordination environments are discussed in detail. The physical origin of the observed spectral features is explored through the machinery of natural difference orbitals. This analysis provides valuable information with respect to the core to valence, metal to metal charge transfer, and metal to ligand charge transfer characters of the relativistically corrected many particle states. The influence of the above electronic effects to the spectral shapes and the size of the treated clusters are thoroughly investigated.

L-edge sum rule analysis on 3d transition metal sites: from d10 to d0 and towards application to extremely dilute metallo-enzymes.

According to L-edge sum rules, the number of 3d vacancies at a transition metal site is directly proportional to the integrated intensity of the L-edge X-ray absorption spectrum (XAS) for the corresponding metal complex. In this study, the numbers of 3d holes are characterized quantitatively or semi-quantitatively for a series of manganese (Mn) and nickel (Ni) complexes, including the electron configurations 3d10→ 3d0. In addition, extremely dilute (<0.1% wt/wt) Ni enzymes were examined by two different approaches: (1) by using a high resolution superconducting tunnel junction X-ray detector to obtain XAS spectra with a very high signal-to-noise ratio, especially in the non-variant edge jump region; and (2) by adding an inert tracer to the sample that provides a prominent spectral feature to replace the weak edge jump for intensity normalization. In this publication, we present for the first time: (1) L-edge sum rule analysis for a series of Mn and Ni complexes that include electron configurations from an open shell 3d0 to a closed shell 3d10; (2) a systematic analysis on the uncertainties, especially on that from the edge jump, which was missing in all previous reports; (3) a clearly-resolved edge jump between pre-L3 and post-L2 regions from an extremely dilute sample; (4) an evaluation of an alternative normalization standard for L-edge sum rule analysis. XAS from two copper (Cu) proteins measured using a conventional semiconductor X-ray detector are also repeated as bridges between Ni complexes and dilute Ni enzymes. The differences between measuring 1% Cu enzymes and measuring <0.1% Ni enzymes are compared and discussed. This study extends L-edge sum rule analysis to virtually any 3d metal complex and any dilute biological samples that contain 3d metals.

Operando Soft X-ray Absorption Spectroscopic Study on a Solid Oxide Fuel Cell Cathode during Electrochemical Oxygen Reduction.

An operando soft X-ray absorption spectroscopic technique, which enabled the analysis of the electronic structures of the electrode materials at elevated temperature in a controlled atmosphere and electrochemical polarization, was established and its availability was demonstrated by investigating the electronic structural changes of an La2 NiO4+δ dense-film electrode during an electrochemical oxygen reduction reaction. Clear O K-edge and Ni L-edge X-ray absorption spectra could be obtained below 773 K under an atmospheric pressure of 100 ppm O2 /He, 0.1 % O2 /He, and 1 % O2 /He gas mixtures. Considerable spectral changes were observed in the O K-edge X-ray absorption spectra upon changing the PO2 and application of electrical potential, whereas only small spectral changes were observed in Ni L-edge X-ray absorption spectra. A pre-edge peak of the O K-edge X-ray absorption spectra, which reflects the unoccupied partial density of states of Ni 3d-O 2p hybridization, increased or decreased with cathodic or anodic polarization, respectively. The electronic structural changes of the outermost orbital of the electrode material due to electrochemical polarization were successfully confirmed by the operando X-ray absorption spectroscopic technique developed in this study.

Iron L-Edge Absorption Spectroscopy of Iron Pentacarbonyl and Ferrocene in the Gas Phase.

Fe L-edge X-ray absorption spectra of gas-phase iron pentacarbonyl and ferrocene measured in total-ion yield mode are reported. Comparison to previously published spectra of free iron atoms and gaseous iron chloride demonstrates how the interplay of local atomic multiplet effects and orbital interactions in the metal-ligand bonds varies for the different systems. We find changes in the degree of metal-ligand covalency to be reflected in the measured 2p absorption onset. Orbital- or state-specific fragmentation is furthermore investigated in iron pentacarbonyl and ferrocene by analyzing the partial-ion-yield spectra at the Fe L-edge. Strong dependence of the yields of different fragments is observed in ferrocene in contrast to iron pentacarbonyl. This difference is attributed to the different degrees to which the 2p core hole is screened in the two systems and to which charge is rearranged in the Auger final states. We provide experimental benchmark spectra for new ab initio approaches for calculating metal L-edge absorption spectra of metal complexes.