First-row Transition Metal Research Articles

Orbital entanglement and the double d-shell effect in binary transition metal molecules.

Accurate modeling of transition metal-containing compounds is of great interest due to their wide-ranging and significant applications. These systems present several challenges from an electronic structure perspective, including significant multi-reference characters and many chemically relevant orbitals. A further complication arises from the so-called double d-shell effect, which is known to cause a myriad of issues in the treatment of first-row transition metals with both single- and multi-reference methods. While this effect has been well documented for several decades, a comprehensive understanding of its consequences and underlying causes is still evolving. Here, we characterize the second d-shell effect by analyzing the information entropy of correlated wavefunctions in a periodic series of 3d and 4d transition metal molecular hydrides and oxides. These quantum information techniques provide unique insight into the nuanced electronic structure of these species and are powerful tools for the study of weak and strong correlations in the transition metal d manifold.

Repurposing First-Row Transition Metal Carbon Dioxide Reduction Electrocatalysts for Electrochemical Carboxylation of Benzyl Chloride

Repurposing First-Row Transition Metal Carbon Dioxide Reduction Electrocatalysts for Electrochemical Carboxylation of Benzyl Chloride

Electrocatalysis of Oxygen Evolution Reaction Promoted by CoNiMn Films Synthesized by Electrodeposition.

Recently, efforts have been made to address the environmental damage caused by fossil-fuel-based primary energy sources. Interest in efficient technologies for converting and storing energy using renewable sources, especially sunlight, has increased, with the aim of replicating the natural photosynthesis process. However, artificial photosynthesis faces challenges with unfavorable kinetics and thermodynamics, requiring the use of stable catalysts for the hydrogen evolution (HER) and oxygen evolution (OER) reactions to generate H2 and O2, respectively. OER is the most prohibitive of the half-reactions by the highly sluggish kinetics. Mixed oxides, particularly those based on first-row transition metals, have shown promising results as catalysts for the OER. This work reports the synthesis of CoNiMn oxide via electrodeposition on fluoride tin oxide followed by electrochemical activation. This approach seeks to explore the synergistic effect between the elements and to produce a catalyst with superior efficiency and stability for the electrocatalysis of the OER compared to the monometallic and bimetallic oxides. The CoNiMn film was structurally and electrochemically characterized. The electrodeposited CoNiMn hybrid films demonstrated low overpotentials compared with standard OER electrocatalysts, with CoNiMn films outperforming all single and bimetallic oxide films. The activated CoNiMn film required an overpotential of 100 mV at 10 mA cm-2 (430 mV at 25 mA cm-2) and Tafel slope of 58 mV dec-1. The film was active for 15 h at 100 mA cm-2 and showed no significant change in morphology and structure after the chronopotentiometry, indicating that it is a promising and cost-effective alternative to enhance the OER activity using abundant elements.

Ancillary Ligand-Promoted Charge Transfer in Bis-indole Pyridine Ligand-Based Nickel Complexes.

There is growing demand for the utilization of first-row transition metal complexes in light-driven processes instead of their conventional noble metal counterparts due to the greater sustainability of first-row transition metal complexes. However, their major drawback is the ultrafast lifetime of the electronic excited states of these first-row transition metal complexes, particularly those of d8 square-planar systems such as Ni(II) complexes, wherein low-lying metal-centered (MC) states provide the deactivation pathway. To increase the excited-state lifetime and broaden their applications, it is important to develop sterically bulky, strong field ligands with low-lying π* orbitals and a highly σ-donating nature to augment the energy of MC states. The current strategy relies on synthetically carbene-based ligands, which are substitutionally cumbersome and act as σ-donors only. In this work, we introduce a bis-indole pyridine (H2BIP) ligand framework, whose dianionic congener (BIP) demonstrates the ability to form stronger covalent bonds with a Ni(II) center compared to neutral donors like carbene and its effect on the complex to produce a less distorted excited-state structure. When conjoined with ancillary ligands such as pyridine or lutidine, the BIP ligand orchestrates the formation of low-energy 3CT states, which decay in ∼40 ps.

Supported Nickel Nanoparticles as Catalyst in Direct sp3 C-H Alkylation of 9H-Fluorene Using Alcohols as Alkylating Agent.

Herein, we report an inexpensive first-row transition metal Ni heterogeneous catalytic system for the Csp3-mono alkylation of fluorene using alcohols as alkylating agents via borrowing hydrogen strategy. The catalytic protocol displayed versatility with high yields of the desired products using various types of primary alcohols, including aryl/hetero aryl methanols, and aliphatic alcohols as alkylating agents. The catalyst Ni NPs@N-C was synthesized via high-temperature pyrolysis strategy, using ZIF-8 as the sacrificial template. The Ni NPs@N-C catalyst was characterized by XPS, HR-TEM, HAADF-STEM, XRD and ICP-MS. The catalyst is stable even in the air at room temperature, displayed excellent activity and could be recycled 5 times without appreciable loss in its activity.

Theoretical Investigation of Electric Polarizability in Porphyrin-Zinc and Porphyrin-Zinc-Thiazole Complexes Using Small Property-Oriented Basis Sets.

Porphyrin complexes are of great importance due to their possible applications as sensors, solar cells and photocatalysts, as well as their ability to bind additional ligands. A valuable source of knowledge on their nature is their electric properties, which can be evaluated employing density functional theory (DFT) methods, supporting the experimental research. The present work aims at the application of small property-oriented basis sets in calculation of electric properties in transition metals, their oxides and test coordination complexes. Firstly, the existing polarized ZPol basis set for the first-row transition metals is modified in order to improve atomic polarizability results. For this purpose, optimization of the f-type polarization function exponent is carried out with respect to the value of average atomic polarizability of investigated metals. Next, both the original and the modified basis sets are employed in finite field CCSD(T) calculation of transition metal oxides' dipole moments, as well as DFT calculation of polarizabilities in porphyrin-zinc and porphyrin-zinc-thiazole complexes. The obtained results show that the ZPol and ZPol-A basis sets can be successfully employed in the calculation of linear electric properties in large systems. The optimization procedure used in the present work can be employed for other source basis sets and elements, leading to new efficient polarized basis sets.

Systematic study of first-row transition metals chlorides as reaction accelerators for Mg/ MgH2 for hydrogen storage application

Mg has been proposed as a possible hydrogen storage material. However, Mg necessarily requires the addition of a suitable material with catalytic activity to improve hydriding and dehydriding reactions. Some chlorides of transition metals have been tested as improvers of hydriding/dehydriding reactions in Mg/MgH2. However, experimental preparation and tested conditions are dissimilar among different published reports. A systematic study of first-row transition metal chlorides as additives is presented here to understand the various factors affecting the hydriding/dehydriding reactions in Mg/MgH2 prepared and tested under the same conditions. The added transition metal chlorides (TMClx, x = oxidation state) include metals in oxidation states +4, +3, and +2 whenever commercially available. Additional chlorides, such as ZrCl4 and AlCl3, were included for comparison. The mixtures of Mg-TMClx were produced employing cryogenic ball milled and characterized by i) temperature-programmed hydriding and dehydriding, ii) X-ray photoelectron spectroscopy at Mg, transition metals, and chlorine 2p edges, iii) X-ray diffraction, and iv) scanning electron microscope. The best additives are VCl3>TiCl4>NiCl2>AlCl3. In contrast, the worst additives among the first-row transition metal chlorides were CrCl2, ZnCl2, and CuCl2. They do not improve at all the hydrogen uptake kinetics of pure Mg. Chemical state, side reactions, crystal structure, and morphology were discussed as factors affecting the behavior of the hydriding and dehydriding reactions. A complex interrelationship among these factors is observed. However, the electronegativity of the transition metal and an interaction of the type Mg-TM-Cl, are proposed as the main factors for the observed improvement of hydriding and dehydriding reactions.

A prediction of high temperature magnetic coupling in transition metal phthalocyanines.

In spintronics, a perennial goal has been the generation of organic spin-bearing semiconductor materials with magnetic ordering stable at room temperature. To this end, the class of transition metal phthalocyanines has shown much promise in fulfilling this ambition. In particular, alpha-phase cobalt (II) phthalocyanine (α-CoPc) exhibits strong antiferromagnetic exchange interactions producing a long range order up to ∼100K. However, the underlying mechanism by which this magnetic interaction proceeds is not well understood. In this report, a simple mechanism has been proposed based on the Hubbard Hamiltonian, which elucidates the exchange coupling in α-CoPc. The mechanism provides stipulations for increasing the magnetic coupling, and this directs to a proposal that substitution of the central cobalt ion for rhodium will lead to a significant increase in coupling strength. The strength of this exchange interaction has been evaluated using broken symmetry hybrid exchange density functional theory and indicates that the novel rhodium (II) phthalocyanine system is indeed predicted to exhibit significantly stronger magnetic ordering. This study, therefore, identifies the coupling mechanism in α-CoPc as primarily attributable to kinetic exchange, explains its previously reported strong coupling relative to its first-row transition metal counterparts, and suggests that rhodium (II) phthalocyanine is likely to exhibit stable magnetic ordering at room temperature.

Photo- and Electrocatalytic Hydrogen Evolution by Heteroleptic Dirhodium(II,II) Complexes: Role of the Bridging and Diimine Ligands.

A series of heteroleptic Rh2(II,II) complexes, cis-[Rh2(μ-DPhF)2(μ-bncn)2]2+ (1; bncn = benzo[c]cinnoline), cis-[Rh2(μ-DPhF)(μ-OAc)(μ-bncn)2]2+ (2), and cis-[Rh2(μ-OAc)2(μ-bncn)2]2+ (3), is presented, and the excited state and redox properties of each complex was characterized for the photo- and electrocatalytic production of H2. The oxidation potentials shift anodically from 1 to 3, consistent with a highest occupied molecular orbital (HOMO) with significant metal-ligand mixing, Rh2(δ*)/DPhF(π/nb). In contrast, modest differences in the first two bncn-localized reversible reduction potentials were observed in 1 - 3. The lowest energy metal/ligand-to-ligand charge transfer (1ML-LCT) transition, Rh2(δ*)/DPhF(π/nb) → bncn(π*), shifts from 633 nm in 1 to 553 nm in 2, and the metal-to-ligand charge transfer (1MLCT) Rh2(π*) → bncn(π*) absorption in 3 appears at 462 nm in CH3CN. Although the 3ML-LCT excited state of 2 is shorter lived than that of 1, 2.7 ns as compared to 19 ns, respectively, photocatalytic hydrogen generation is observed for the former upon 595 nm irradiation in the presence of 0.1 M TsOH (p-tolylsulfonic acid) and 0.1 M BNAH (1-benzyl-1,4-dihydronicotinamide). The temperature dependence of the 3ML-LCT lifetimes of 1 and 2 shows the presence of a thermally accessible deactivating state. In addition, the singly reduced intermediate, [2]-, is photoactive and able to generate hydrogen in the presence of TsOH. Importantly, the electrocatalytic currents generated by equimolar concentrations of 1 - 3 in CH3CN are nearly identical, consistent with a mechanism of catalysis that is localized on the bncn ligand and does not require a Rh-H hydride intermediate. This finding can be used to develop earth-abundant first-row transition metal complexes for photo- and electrocatalytic H2 production.

Strategies and Mechanisms of First-Row Transition Metal-Regulated Radical C-H Functionalization.

Radical C-H functionalization represents a useful means of streamlining synthetic routes by avoiding substrate preactivation and allowing access to target molecules in fewer steps. The first-row transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) are Earth-abundant and can be employed to regulate radical C-H functionalization. The use of such metals is desirable because of the diverse interaction modes between first-row transition metal complexes and radical species including radical addition to the metal center, radical addition to the ligand of metal complexes, radical substitution of the metal complexes, single-electron transfer between radicals and metal complexes, hydrogen atom transfer between radicals and metal complexes, and noncovalent interaction between the radicals and metal complexes. Such interactions could improve the reactivity, diversity, and selectivity of radical transformations to allow for more challenging radical C-H functionalization reactions. This review examines the achievements in this promising area over the past decade, with a focus on the state-of-the-art while also discussing existing limitations and the enormous potential of high-value radical C-H functionalization regulated by these metals. The aim is to provide the reader with a detailed account of the strategies and mechanisms associated with such functionalization.

Comparative Assessment of First-Row 3d Transition Metals (Ti-Zn) Supported on CeO2 Nanorods for CO2 Hydrogenation

Comparative Assessment of First-Row 3d Transition Metals (Ti-Zn) Supported on CeO2 Nanorods for CO2 Hydrogenation

Mechanistic Insight of High-Valent First-Row Transition Metal Complexes for Dehydrogenation of Ammonia Borane.

Designing an efficient and cost-effective catalyst for ammonia borane (AB) dehydrogenation remains a persistent challenge in advancing a hydrogen-based economy. Transition metal complexes, known for their C-H bond activation capabilities, have emerged as promising candidates for AB dehydrogenation. In this study, we investigated two recently synthesized C-H activation catalysts, 1 (CoIV-dinitrate complex) and 2 (NiIV-nitrate complex), and demonstrated their efficacy for AB dehydrogenation. Using density functional theory calculations and a detailed analysis, we elucidated the AB dehydrogenation mechanism of these complexes. Our results revealed that both complexes 1 and 2 can efficiently dehydrogenate AB at room temperature, although the abstraction of molecular H2 from these complexes requires slightly elevated temperatures. We utilized H2 binding free energy calculations to identify potentially active sites and observed that complex 2 can release two equivalents of H2 at a temperature slightly higher than room temperature. Furthermore, we investigated AB dehydrogenation kinetics and thermodynamics in iron (Fe)-substituted systems, complexes 3 and 4. Our results showed that the strategic alteration of the central metal atom, replacing Ni in complex 2 with Fe in complex 4, resulted in enhanced kinetics and thermodynamics for AB dehydrogenation in the initial cycle. These results underscore the potential of high-valent first-row transition metal complexes for facilitating AB dehydrogenation at room temperature. Additionally, our study highlights the beneficial impact of incorporating iron into such mononuclear systems, enhancing their catalytic activity.

Coordination variety of phenyltetrazolato and dimethylamido ligands in dimeric Ti, Zr, and Ta complexes.

Three structurally diverse 5-phenyltetrazolato (Tz) Ti, Zr, and Ta complexes, namely, (C2H8N)[Ti2(C7H5N4)5(C2H6N)4]·1.45C6H6 or (Me2NH2)[Ti2(NMe2)4(2,3-μ-Tz)3(2-η1-Tz)2]·1.45C6H6, (1·1.45C6H6), [Zr2(C7H5N4)6(C2H6N)2(C2H7N)2]·1.12C6H6·0.382CH2Cl2 or [Zr2(Me2NH)2(NMe2)2(2,3-μ-Tz)3(2-η1-Tz)2(1,2-η2-Tz)]·1.12C6H6·0.38CH2Cl2 (2·1.12C6H6·0.38CH2Cl2), and (C2H8N)2[Ta2(C7H5N4)8(C2H6N)2O]·0.25C7H8 or (Me2NH2)2[Ta2(NMe2)2(2,3-μ-Tz)2(2-η1-Tz)6O]·0.25C7H8 (3·0.25C7H8), where TzH is 5-phenyl-1H-tetrazole, have been synthesized and structurally characterized. All three complexes are dinuclear; the Ti center in 1 is six-coordinate, whereas the Zr and Ta atoms in 2 and 3 are seven-coordinate. The coordination environments of the Ti centers in 1 are similar, and so are the ligations of the Ta centers in 3. In contrast, the two Zr centers in 2 bear a different number of ligands, one of which is a bidentate η2-5-phenyltetrazolato ligand that has not been observed previously for d-block elements. The dimethylamido ligand, present in the starting materials, remained unchanged, or was converted to dimethylamine and dimethylammonium during the synthesis. Dimethylamine coordinates as a neutral ligand, whereas dimethylammonium is retained as a hydrogen-bonded entity bridging Tz ligands.

Hybrid spin-orbit exciton-magnon excitations in FePS3

FePS3 is a layered van der Waals (vdW) Ising antiferromagnet that has recently been studied in the context of true 2D magnetism and emerged as an ideal material platform for investigating strong spin-phonon coupling, and non-linear magneto-optical phenomena. In this work, we demonstrate an important unresolved role of spin-orbit coupling (SOC) in the ground state and excitations of this compound. Combining first-principles calculations with linear flavor wave theory (LFWT), we find strong mixing and spectral overlap of different spin-orbital single-ion states. Low-lying excitations form hybrid spin-orbit exciton/magnon modes. Complete parameterization of the low-energy model requires nearly half a million coupling constants. Despite this complexity, such a model can be inexpensively derived using local many-body-based approaches, which yield quantitative agreement with recent experiments. The results highlight the importance of SOC even in first-row transition metals and provide essential insight into the properties of 2D magnets with unquenched orbital moments.

Unveiling the Role of Dopants in the Electrochemical Ozone Production Reaction Using Tin Oxide Electrodes

Ozone is a strong oxidizer with promising environmentally friendly applications in water disinfection, air purification, and organic synthesis. The 6-e- electrochemical ozone production (EOP) reaction offers great potential for ozone generation while curbing the formation of harmful by-products compared to other ozone production methods. However, the development of electrochemical ozone production (EOP) catalysts is limited by significant hurdles dictated by thermodynamic limitations. In this work, we develop and validate a comprehensive guideline that outlines a strategic and rational design approach to induce EOP activity in tin oxide. We propose that two things are needed for tin oxide to produce ozone: increased conductivity, achieved with donor dopants, and first-row transition metal (TM) dopants to facilitate hydroperoxyl radical generation through Fenton-like processes. To validate our approach, we picked tantalum, antimony, and tungsten as donor dopants and nickel and cobalt as transition metals. Our results suggest that all combinations of TMs, oxidizable to a cationic state capable of producing hydroperoxyl radicals from hydrogen peroxide, and donor dopants lead to EOP activity in tin oxide.

(Invited) Electrocatalysts for the Oxygen Reduction Reaction and the Hydrogen Evolution Reaction Based on “Core-Shell”, “PGM-Free” Carbon Nitride Systems

The key electrochemical processes at the heart of the “hydrogen economy” involve: (i) the recombination of hydrogen and oxygen to form water in fuel cells (FCs); and (ii) the splitting of water to yield hydrogen and oxygen in water electrolyzers (ELs). Depending on the particular device taken under consideration, such processes typically occur either in a highly acidic environment (e.g., in proton-exchange membrane fuel cells, PEMFCs, and in proton-exchange membrane electrolyzers, PEMELs) or in strongly alkaline conditions (e.g., in anion-exchange membrane fuel cells, AEMFCs; and in anion-exchange membrane electrolyzers, AEMELs). In both cases, such processes require suitable electrocatalysts (ECs) to minimize overpotentials and achieve a performance and durability level compatible with applications. State-of-the-art ECs for both FCs and ELs typically suffer from important drawbacks such as: (i) high overpotentials; (ii) a poor durability; and (iii) a high loading of strategic elements, with a particular reference to platinum-group metals (PGMs); correspondingly, significant concerns are raised due to potential supply bottlenecks.In this work, a new family of “PGM-free” ECs is proposed, especially targeted to promote the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER) in either/both the acidic and the alkaline environment. The ECs are obtained by means of a multi-step synthetic process [1]. In the first step a precursor is prepared by coupling a carbon black support with a hybrid inorganic-organic macromolecular system consisting of an organic binder coordinating: (i) a first-row transition metal (e.g., Fe) meant to act as the “catalyst”; and (ii) Sn, playing the role of “co-catalyst”. Subsequently the precursor undergoes a multi-step pyrolysis process followed by suitable chemical treatments meant to remove labile species and reaction byproducts, yielding the final EC. Optionally, the EC may be coupled with an additional aliquot of the hybrid-inorganic precursor. In this case, further pyrolysis/chemical treatment steps are carried out to obtain the final product.The final “PGM-free” ECs proposed herein exhibit a “core-shell” morphology. The carbon black “core” is covered by a carbon nitride “shell” stabilizing the active sites based on the “catalyst” and the “co-catalyst” into C- and N- “coordination nests”. The ECs undergo an extensive physicochemical characterization, meant to determine: (i) the chemical composition, both in the bulk and on the surface (adopting analytical techniques such as ICP-AES, CHNS microanalysis, EDX and NAP-XPS); (ii) the morphology (by means of UHR-SEM); (iii) the porosimetric features (by nitrogen and water physisorption studies); and (iv) the structure (e.g., through wide-angle X-ray diffraction). The kinetics and reaction mechanism of the proposed ECs in the ORR and HER are determined by advanced electroanalytical techniques, with a particular reference to cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE). The synthetic parameters are finally correlated with the results of the physicochemical and the electrochemical characterization, shedding light on the most promising avenues to guide the preparation of further ECs exhibiting improved performance and durability, suitable for implementation in next-generation FCs and ELs.

Developing Terpyridine-Based Metal Complexes for Non-Aqueous Redox Flow Batteries

Redox flow batteries (RFBs) that utilize dissolved electroactive materials have shown great potential in storing intermittent solar and wind energy. The unique technological advantages of decoupled energy and power lead to high flexibility and scalability in RFB design, making it possible to satisfy a wide range of energy and power applications.[1,2] In traditional RFBs, inorganic transition-metal salts like all-vanadium, iron-chromium, and zinc-bromine RFBs are commonly used.[3,4] However, the narrow electrochemical stability window of water limits the attainable cell voltages in these aqueous systems. [5,6] To overcome these limitations, recent research has shifted towards non-aqueous RFBs (NARFBs) that use non-aqueous solvents, which can offer a wider electrochemical window up to 5 V.[7,8] Here, we introduce our research efforts on the design and synthesis of a series of terpyridine-based complexes of the first-row transition metals Cr, Mn, Fe, and Co for non-aqueous redox flow batteries (NARFBs). Electrochemical studies reveal that these complexes can undergo multi-electron transfer redox reactions. Notably, the Mn and Fe-based complexes exhibit both low negative redox potentials and high positive redox potential, enabling them to serve as a bipolar electrolyte for symmetric RFBs with a cell voltage of over 2 V. The assembled iron-based symmetric NARFB demonstrates a high cell voltage of 2.3 V, columbic efficiency of 97%, energy efficiency as high as 88%, and stable charge-discharge capacity retention of 60% after 160 cycles, corresponding to 99.75 % capacity retention per cycle. Figure 1

Dynamic Activity and Stability of Transition Metal (oxy)Hydroxide Oxygen Evolution Electrocatalysts Under Steady and Intermittent Operation

The oxygen evolution reaction (OER) plays a critical role in several energy conversion technologies, requiring catalysts that combine high activity with stability for successful commercialization. Catalysts from first-row transition metal oxides have garnered considerable attention in this context. Their noteworthy OER activity and stability in alkaline environments position them as a more economical option than their counterparts in acidic media. However, recent studies have shown that these materials tend to experience significant dissolution issues and undergo changes in their chemical composition, a phenomenon observed even during steady-state operation.1–3 Addressing these challenges is essential for advancing commercial energy conversion technologies, which often face intermittent loads and reverse currents. A deeper understanding of the dynamic reconstruction under fluctuating conditions is crucial for developing more durable and efficient electrocatalytic materials.4 In this work, we investigate the dynamic performance of nickel cobalt (oxy)hydroxide electrocatalytic films containing iron active sites in alkaline media under steady and intermittent operation. First, we systematically examine the changes in OER catalytic activity in a typical three-electrode configuration, focusing on the incorporation and redissolution of iron and cerium during different electrochemical conditioning methods. As shown in Figure 1a, conditioning using chronopotentiometry decreases the OER overpotential without significantly shifting the redox peak. In contrast, conditioning using cyclic voltammetry significantly shifts the redox peak position (Figure 1b). These differences are attributed to the (oxy)hydroxide film thickness, which forms in situ during conditioning and affects the Fe dissolution and incorporation rates based on the conditioning method.5 We use different analytical techniques to probe chemical transformations during conditioning. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are utilized to analyze compositional changes in the electrocatalytic films. Moreover, inductively coupled plasma mass spectrometry (ICP-MS) tracks metal dissolution.Next, we utilize an electrochemical flow electrolyzer with a zero-gap configuration, integrated with online ICP-MS and post-experimental TOF-SIMS and XPS, to study the reconstruction of these electrocatalysts under intermittent conditions. A NiFe anode operating in 6 M KOH with 1 ppm of Fe3+ shows a 40-mV change after 120 cycles of alternating low and high currents, including a simulated shutdown step (Figure 1c). This cell potential change, becoming more negative with continued cycling (Figure 1d), is attributed to the shutdown step. Our findings underscore how operating conditions affect the dynamic reconstruction of electrocatalytic materials, offering critical insights for developing more robust and resilient materials suitable for commercial applications.

Establishing the origin of Marcus-inverted-region behaviour in the excited-state dynamics of cobalt(III) polypyridyl complexes.

Growing interest in the use of first-row transition metal complexes in a number of applied contexts-including but not limited to photoredox catalysis and solar energy conversion-underscores the need for a detailed understanding of their photophysical properties. A recent focus on ligand-field photocatalysis using cobalt(III) polypyridyls in particular has unlocked unprecedented excited-state reactivities. Photophysical studies on Co(III) chromophores in general are relatively uncommon, and so here we carry out a systematic study of a series of Co(III) polypyridyl complexes in order to delineate their excited-state dynamics. Compounds with varying ligand-field strengths were prepared and studied using variable-temperature ultrafast transient absorption spectroscopy. Analysis of the data establishes that the ground-state recovery dynamics are operating in the Marcus inverted region, in stark contrast to what is typically observed in other first-row metal complexes. The analysis has further revealed the underlying reasons driving this excited-state behaviour, thereby enabling potential advancements in the targeted use of the Marcus inverted region for a variety of photolytic applications.

High-Pressure Synthesis and Recovery of Single Crystals of the Metastable Manganese Carbide, MnCx.

Transition metal carbides find widespread use throughout industry due to their high strength and resilience under extreme conditions. However, they remain largely limited to compounds formed from the early d-block elements, since the mid-to-late transition metals do not form thermodynamically stable carbides. We report here the high-pressure bulk synthesis of large single crystals of a novel metastable manganese carbide compound, MnCx (P63/mmc), which adopts the anti-NiAs-type structure with significant substoichiometry at the carbon sites. We demonstrate how synthesis pressure modulates the carbon loading, with ~40 % occupancy being achieved at 9.9 GPa.