D-electron Configuration Research Articles

Modulation of electronic spin state and construction of dual-atomic tandem reaction for enhanced pH-universal oxygen reduction

Combining both advances of electronic spin state modulation and tandem reaction mechanism, an atomic-level dual iron-copper catalyst is designed for enhanced oxygen reduction capability. Herein, the intense interaction between the iron-copper site and its coordination environment can not only controls the flow of external charge at the atomic level, but regulates the internal 3d electron configuration. These modulations can optimize the orbital interaction and pair hardness (ηDA) between the acceptor and the donor, and achieves a fast tandem reaction kinetics, thereby surmounting the limitation of Scaling Relation. The as-prepared bimetal catalyst validates a high ORR activity and stability, which even exceed those of the benchmark Pt/C in pH-universal electrolytes. Meanwhile, Fe,Cu/N-C driven Zn-air batteries in alkaline and neutral electrolytes show prominent performance with peak power densities of 173.7 mW cm−2 and 86.5 mW cm−2. This work provides a useful design principle for developing or optimizing other efficient ORR catalysts.

Role of water structural properties in interaction of amino acids with metal ions of varying size and electrons in d-block or main group elements: Quantitative thermodynamic analysis

Interactions of a homologous series of amino acids (glycine, l-alanine, DL-α-amino-n-butyric acid, l-valine and l-leucine) with salts (LiCl, NaCl, KCl, CaCl2, MnCl2, CoCl2) having common anion, but cation having varying d-electronic configuration and alkaline earth metals have been studied in aqueous solutions employing ultrasensitive isothermal titration calorimetry. Standard molar enthalpies of amino acid-salt interactions have been interpreted in terms of predominant ionic association between charged centres and the corresponding desolvation penalty. Extra crystal field stabilization experienced by Mn2+(aq) and Ca2+(aq) due to d5 and d10 electronic configuration has been addressed based on results of standard molar enthalpies of interaction. The results indicate significant desolvation cost predominantly from hydration of the cations of the salts rather than from hydration of zwitter-ionic ends of the amino acids irrespective of their chain length. This is also indicated by stronger endothermic interaction of the amino acids with the bivalent cations than that with the monovalent ones. The results obtained in this work provide essential mechanistic insights into nature of amino acid interactions modulated by variation in cationic d-electronic configuration in terms of enthalpies of interaction.

LNL-Carbazole Pincer Ligand: More than the Sum of Its Parts.

The utility of carbazole in photo-, electro-, and medicinal applications has ensured its widespread use also as the backbone in tridentate pincer ligands. In this review, the aim is to identify and illustrate the key features of the LNL-carbazolide binding to transition metal centers (with L = flanking donor moieties, e.g., C, N, P, and O-groups) in a systematic bottom-up progression to illustrate the marked benefits attainable from (i) the rigid aromatic carbazole scaffold (modulable in both the 1,8- and 3,6-positions), (ii) the significant electronic effect of central carbazole-amido binding to a metal, and the tunable sterics and electronics of both the (iii) flanking donor L-moieties and (iv) the wingtip R-groups on the L-donors, with their corresponding influence on metal coordination geometry, d-electron configuration, and resultant reactivity. Systematic implementation of the ligand design strategies not in isolation, but in a combinatorial approach, is showcased to demonstrate the potential for functional molecules that are not only modulable but also adaptable for wide-ranging applications (e.g., stereoselective (photo)catalysis, challenging small molecule activation, SET and redox applications, and even applications in chemotherapeutics) as an indication of future research efforts anticipated to stem from this versatile pincer assembly, not only for the transition metals but also for s-, p-, and f-block elements.

Electronic properties and redox chemistry ofN-confused metalloporphyrins

Here we study the effect of metals on the characteristic Soret band of N-confused porphyrins. We used DFT calculations to study how this low-lying region of the spectrum of the NCP-2H isomer is affected by the introduction of transition metals with various ([Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] d-electron configurations. The spin ground state of these complexes is mostly dependent on the number of unpaired electrons, both with and without the presence of an axial ligand. The analysis of the electronic distribution and spin density showed that these unpaired electrons are often harbored by the N-confused porphyrin ring instead of on the metal. Time-dependent DFT results indicated that the aromatic system of porphyrin is disrupted in the N-confused isomer: instead of the typical large Soret band, this now gives rise to two peaks of much lower intensity. Most metallo-porphyrins exhibited similar optical properties, with the HOMO/LUMO orbitals showing a mixed metal/porphyrin character. The only exception was the Rh metalloporphyrin that exhibited a ligand-to-metal charge transfer band with increasing intensity as function of the ligand field. This suggests Rh is the only metal whose orbitals are higher in energy than the ligand’s, indicating that it is the only system where the redox processes occur on the metal.

Metal-Carbodithioate-Based 3D Semiconducting Metal-Organic Framework: Porous Optoelectronic Material for Energy Conversion.

Solar energy conversion requires the working compositions to generate photoinduced charges with high potential and the ability to deliver charges to the catalytic sites and/or external electrode. These two properties are typically at odds with each other and call for new molecular materials with sufficient conjugation to improve charge conductivity but not as much conjugation as to overly compromise the optical band gap. In this work, we developed a semiconducting metal-organic framework (MOF) prepared explicitly through metal-carbodithioate "(-CS2)nM" linkage chemistry, entailing augmented metal-linker electronic communication. The stronger ligand field and higher covalent character of metal-carbodithioate linkages─when combined with spirofluorene-derived organic struts and nickel(II) ion-based nodes─provided a stable, semiconducting 3D-porous MOF, Spiro-CS2Ni. This MOF lacks long-range ordering and is defined by a flexible structure with non-aggregated building units, as suggested by reverse Monte Carlo simulations of the pair distribution function obtained from total scattering experiments. The solvent-removed "closed pore" material recorded a Brunauer-Emmett-Teller area of ∼400 m2/g, where the "open pore" form possesses 90 wt % solvent-accessible porosity. Electrochemical measurements suggest that Spiro-CS2Ni possesses a band gap of 1.57 eV (σ = 10-7 S/cm at -1.3 V bias potential), which can be further improved by manipulating the d-electron configuration through an axial coordination (ligand/substrate), the latter of which indicates usefulness as an electrocatalyst and/or a photoelectrocatalyst (upon substrate binding). Transient-absorption spectroscopy reveals a long-lived photo-generated charge-transfer state (τCR = 6.5 μs) capable of chemical transformation under a biased voltage. Spiro-CS2Ni can endure a compelling range of pH (1-12 for weeks) and hours of electrochemical and photoelectrochemical conditions in the presence of water and organic acids. We believe this work provides crucial design principles for low-density, porous, light-energy-conversion materials.

The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First‐Row Transition Metal Complexes

AbstractThe expansion of d‐orbitals as a result of metal‐ligand bond covalence, the so‐called nephelauxetic effect, is a well‐established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first‐row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In CrIII and MnIV complexes with the d3 valence electron configuration, the nephelauxetic effect was exploited to shift the well‐known ruby‐like red luminescence to the near‐infrared spectral region. In FeII and CoIII complexes with the low‐spin d6 electron configuration, charge‐transfer excited states were stabilized with respect to detrimental metal‐centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d6) isocyanide complexes of Cr0 and MnI, the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first‐row transition metals.

The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First-Row Transition Metal Complexes.

The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first-row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In CrIII and MnIV complexes with the d3 valence electron configuration, the nephelauxetic effect was exploited to shift the well-known ruby-like red luminescence to the near-infrared spectral region. In FeII and CoIII complexes with the low-spin d6 electron configuration, charge-transfer excited states were stabilized with respect to detrimental metal-centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d6 ) isocyanide complexes of Cr0 and MnI , the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first-row transition metals.

Recent Advances in N-Heterocyclic Carbene Coinage Metal Complexes in A3-Coupling and Carboxylation Reaction

Owing of their accessibility and wide range of reactivities, alkynes make for fascinating building blocks. Either a selective alkyne carbon-carbon triple bond reaction or activation of the terminal alkyne C-H bond may be employed to functionalize them. Monocationic coinage metal complexes with a d10 electronic configuration are effective catalysts for alkyne activation. Silver(I) and gold(I) N-heterocyclic (NHC) systems are emerging as promising catalysts in multicomponent alkyne activation reactions; this review paper focuses on A3 (aldehyde-amine-alkyne)-coupling reaction and carbon dioxide fixation, furnishing a systematic overview of the scientific advances achieved during the last two decades. This study will carefully compare the corresponding silver and gold complexes employed in the two processes. The differences in reaction routes brought about by the catalyst ligand structure will be investigated with an emphasis on evaluating the benefits provided by the easily tuneable NHC backbone, in terms of chemo- and stereo-selectivity.

Ethanol-Induced Ni2+ -Intercalated Cobalt Organic Frameworks on Vanadium Pentoxide for Synergistically Enhancing the Performance of 3D-Printed Micro-Supercapacitors.

The synthesis of metal-organic framework (MOF) nanocomposites with high energy density and excellent mechanical strength is limited by the degree of lattice matching and crystal surface structure. In this study, dodecahedral ZIF-67 is synthesized uniformly on vanadium pentoxide nanowires. The influence of the coordination mode on the surface of ZIF-67 in ethanol is also investigated. Benefitting from the different coordination abilities of Ni2+ , Co2+ , and N atoms, spatially separated surface-active sites are created through metal-ion exchange. Furthermore, the incompatibility between the d8 electronic configuration of Ni2+ and the three-dimensional (3D) structure of ZIF-67 afforded the synthesis of hollow structures by controlling the amount of Ni doping. The formation of NiCo-MOF@CoOOH@V2 O5 nanocomposites is confirmed using X-ray absorption fine structure analysis. The high performance of the obtained composite is illustrated by fabricating a 3D-printed micro-supercapacitor, exhibiting a high area specific capacitance of 585 mF cm-2 and energy density of 159.23 µWh cm-2 (at power density = 0.34mW cm-2 ). The solvent/coordination tuning strategy demonstrated in this study provides a new direction for the synthesis of high-performance nanomaterials for electrochemical energy storage applications.

Gradient Strain-Induced Room-Temperature Ferroelectricity in Magnetic Double-Perovskite Superlattices.

Single-phase multiferroics suffer from a fundamental contradiction between polarity and magnetism in d0 electronic configuration, motivating studies of unconventional ferroelectricity in magnetic oxides. However, low critical temperature and polarization still need to be overcome. Here, it is reported that the switchable polarization behavior at room temperature in [(La2 NiMnO6 )/(La2 CoMnO6 )]n double-perovskite magnetic superlattice films is achieved by engineering a microstructure with gradient strains, and the ferromagnetic Curie temperature did not show a rapid decrease. The synergy of gradient strains and superlattice components plays a decisive role in inducing ferroelectricity via the tilting or rotation of various oxygen octahedra. Such distortion responses to gradient strains are accompanied by slight magnetic fluctuations, maximizing the preservation of the initial magnetic exchange interactions, which alleviates the contradiction of multiferroic coexistence to a certain extent. This work confirms the room-temperature ferroelectricity in double-perovskite superlattices and provides a preferred strategy for confronting the difficulty of multiferroic coexistence in single-phase materials.

Explaining Kinetic Trends of Inner-Sphere Transition-Metal-Ion Redox Reactions on Metal Electrodes

Transition-metal ions regularly undergo charge transfer (CT) by directly interacting with electrodes, and this CT governs the performance of devices for numerous applications like energy storage and catalysis. These CT reactions are deemed inner sphere because they involve direct formation of a chemical bond between the electrode and the metal ion. Predicting inner-sphere CT kinetics on electrodes using simple physicochemical descriptors would aid the design of electrochemical systems with improved kinetics. Herein, we report that the average energy of the d electrons (i.e., d-band center) of a transition-metal electrode rationalizes the kinetic trends of inner-sphere CT of transition-metal ions. We demonstrate that V2+/V3+, an important redox reaction for flow batteries, is an inner-sphere reaction and that the kinetic parameters correlate with the adsorption strength of the vanadium intermediate on Au, Ag, Cu, Bi, and W electrodes, with W being the most active electrode reported to date. We show that the adsorption strength of the vanadium intermediate linearly correlates with the d-band center such that the d-band center serves as a simple descriptor for the V2+/V3+ kinetics. We extract kinetic data from the literature for four other inner-sphere CT reactions of metal ions involving Cr-, Fe-, and Co-based complexes to show that the d-band center also linearly correlates with kinetic trends for these systems. The d-band center of the electrode is a general descriptor for heterogeneous inner-sphere CT because it correlates with the adsorption strength of the metal-ion intermediate. The d-band center descriptor is analogous to the d-electron configuration of metal ions serving as a descriptor for homogeneous inner-sphere CT because the d-electron configuration controls bond strengths of intermediate metal-ion complexes.

Copper-Nitrogen-Coordinated Carbon Dots: Transformable Phototheranostics from Precise PTT/PDT to Post-Treatment Imaging-Guided PDT for Residual Tumor Cells

Phototheranostics has attracted considerable attention in the fields of cancer diagnosis and treatment. However, the complete eradication of solid tumors using traditional phototheranostics is difficult because of the limited depth and range of laser irradiation. New phototheranostics enabling precise phototherapy and post-treatment imaging-guided programmed therapy for residual tumors is urgently required. Accordingly, this study developed a novel transformable phototheranostics by assembling hyaluronic acid (HA) with copper-nitrogen-coordinated carbon dots (CDs). In this transformable nanoplatform, named copper-nitrogen-CDs@HA, the HA component enables the specific targeting of cluster determinant (CD) 44-overexpressing tumor cells. In the tumor cells, redox glutathione converts Cu(II) (cupric ions) into Cu(I) (cuprous ions), which confers the novel transformable functionality to phototheranostics. Both in vitro and in vivo results reveal that the near-infrared-light-photoactivated CuII-N-CDs@HA could target CD44-overexpressing tumor cells for precise synergistic photothermal therapy and photodynamic therapy. This study is the first to observe that CuII-N-CDs@HA could escape from lysosomes and be transformed in situ into CuI-N-CDs@HA in tumor cells, with the d9 electronic configuration of Cu(II) changing to the d10 electronic configuration of Cu(I), which turns on their fluorescence and turns off their photothermal properties. This transformable phototheranostics could be used for post-treatment imaging-guided photodynamic therapy on residual tumor cells. Thus, the rationally designed copper-nitrogen-coordinated CDs offer a simple in situ transformation strategy for using multiple-stimulus-responsive precise phototheranostics in post-treatment monitoring of residual tumor cells and imaging-guided programmed therapy.

A hampered oxidative addition of pre-coordinated pincer ligands can favour alternative pathways of activation.

Pre-coordination to a transition metal by the terminal donor groups of a tri-dentate ligand is a common strategy to stabilise elusive groups, to achieve unprecedented bond activation and to develop novel modes of metal-ligand-cooperation for catalysis. In the current manuscript, we demonstrate that the oxidative addition of a central E-H-bond after pre-coordination to the metal centre is disfavoured for metals with d10 electron configuration. For exemplary pincer ligands and metals with d10 electron configuration, quantum chemical calculations suggest a second barrier, which is associated with the rearrangement of the saw-horse structure, obtained after oxidative addition, to the expected square planar geometry for the resulting d8 electron configuration. In the case of PBP-type ligands with a central L2BH2-group (L = R3P) the reaction with Pt0 precursors proceeds via an alternative pathway of activation, which involves the backside attack of a nucleophile to the boron atom, which facilitates the nucleophilic attack of the Pt0 centre and formation of a boryl complex (LBH2). As the corresponding reaction with a PtII precursor leads to B-H- instead of B-L-activation and formation of complex 2 with a L2BH donor, our results show that ligand-stabilized borylenes (L2BH) can in principle be converted to boryls (LBH2) via boronium salts (L2BH2+).

A stable 2D luminescent metal–organic framework as a highly sensitive sensor for Fe3+and Cr2O72−/CrO42−in water

Reacting H4BDPO with d10electronic configuration Cd2+ions under solvothermal conditions produces a 2D MOF, which can serve as a luminescent sensor for sensitively detecting Fe3+and Cr2O72−/CrO42−ions in the natural water system.

Copper-based biological alloys and nanocomposites for enzymatic catalysis and sensing applications.

Copper (Cu) is an inexpensive transition metal on Earth, exhibiting high catalytic activity due to its rich d-electron configuration and variable oxidation states. Cu-based biological alloys and nanocomposites have emerged as a prominent research area. Under specific synthesis conditions, alloys or nanocomposites formed by Cu with other metals demonstrate excellent enzyme-like and sensing activities. These advanced materials offer significant advantages over artificial enzymes in enzymatic applications, including high stability, simple synthesis, flexible catalytic performance, and ease of preservation. In addition, various types of sensors have been designed based on the unique electrochemical properties exhibited by these alloys and nanocomposites as well as their specific reactions with the target substances. These sensors possess advantages such as stability, high efficiency, a broad detection range, low detection limits, and high sensitivity. In this review, we summarize the current research status of Cu-based biological alloys and nanocomposites in enzyme-like applications and sensing applications. Based on this, we introduce the diverse enzyme-like activities exhibited by Cu-based nanozymes prepared under different synthesis conditions and their applications in areas such as biosensing, cancer treatment, and antibacterial therapy. Furthermore, we provide an overview of the applications of Cu-based alloys and nanocomposites in the field of sensing based on their enzyme-like activity or chemical activities. These sensors have been widely employed in biomedical detection, environmental hazardous substance monitoring, and food safety testing. Challenges and prospects faced by Cu-based alloys and nanocomposites are also highlighted for future works.

Recent advances in nonmetallic modulation of palladium-based electrocatalysts

Modulating the electrocatalytic performance of Palladium (Pd) with nonmetallic elements (e.g., H, B, C, N, O, P and S) has gained ever-increasing attention since their introduction has been proven to effectively modulate the 3d-electronic configuration and subsurface properties of Pd. In this review, the most advanced nonmetal-modified Pd-based catalysts are classified according to the different doped atoms (i.e., hydrides, borides, carbides, nitrides, oxides, phosphides and sulfides) and critically reviewed to emphasize the roles of nonmetallic elements doping on various electrocatalytic reactions. In each section, the synthetic strategies developed to incorporate nonmetals are discussed in detail. Furthermore, the optimized approaches of nonmetals-doped Pd-based catalysts and corresponding electrocatalytic enhancement mechanisms were also discussed clearly. Finally, the current challenges and future perspectives regarding nonmetal-modified Pd-based nanocatalysts are also outlined.

Investigations of the structural, magnetic, mechanical, electronic and ferroelectric properties of Mn2MnWO6 double corundum oxide

Materials exhibiting both ferroelectric and ferromagnetic or antiferromagnetic (FM or AFM) ordering are exceptional and are desired for promising applications in future electronic devices. A ferroelectric material Mn2MnWO6 corundum double oxide with AFM magnetic spin order is investigated using density functional theory (DFT). The structure relaxations and optimization confirmed that the non-centrosymmetric (space group R3) is the most stable ground state structure of the compound. The compound is found semiconductor with band gap value 1.8 eV in spin up and 2.47 eV in spin down channel. The electric polarization arises due to d0 electronic configuration of W atom, and the magnetization occurs due to unpaired dn orbital configuration of Mn atom. The large value of polarization 61.98 μC/cm2 and magnetic moments 5.96μB/f.u (f.u = formula unit) of Mn2MnWO6 make it suitable candidate for magneto-electric and ferroelectric applications. The elastic and mechanical calculations show that Mn2MnWO6 is mechanically stable in rhombohedral phase. The calculated piezoelectric coefficient d33 = 528 pC/N is comparable to those of lead based piezoelectric materials.

Incorporating Ni-Polyoxometalate into the S-Scheme Heterojunction to Accelerate Charge Separation and Resist Photocorrosion for Promoting Photocatalytic Activity and Stability.

The emerging polyoxometalate (POM) nanomaterials are transition metal oxygen anion clusters with d0 electronic configurations, which could be attractive and potential photocatalysts. Hence, a nickel (Ni)-substituted polyoxometalate K6Na4[Ni4(H2O)2(PW9O34)2]·32H2O (Ni4POM)-incorporating step (S)-scheme heterojunction was developed to promote photocatalytic activity and stability in H2 and H2O2 production. The multielectron transfer through variable valence metal centers in Ni4POM would facilitate the recombination of invalid charges through the S-scheme pathway. Moreover, incorporating Ni4POM into the S-scheme heterojunction can broaden the light absorption range and meanwhile lead to resistance to photocorrosion to promote the optical and chemical stability of Cd0.5Zn0.5S (CZS). The optimized CZSNi-70 exhibited a H2 evolution rate of 42.32 mmol g-1 h-1 under visible-light irradiation with an apparent quantum yield of 32.27% at 420 nm and a H2O2 production rate of 295.4 μmol L-1 h-1 under 420 nm light-emitting diode irradiation. This work can provide a new view for the development of transition metal-substituted POM-based stable and efficient S-scheme photocatalysts.

Quasi-planar Co atom-doped boron cluster: CoB192.

A global search for the lowest energy structure of CoB192- clusters was conducted. RESULTS: Its ground state is a quasi-planar structure with the Co atom surrounded by a B8 ring. The central Co atom has an oxidation state of +1 with d8 electron configuration. The wave function analysis showed that the Co-B interaction is not a covalent bond. The bonding strength of peripheral B-B bonds is stronger than that of inner ones. The inner B8 ring bonds with outer boron atoms via σ- and π-type bonds. CoB192- shows remarkable aromatic character.

Tunable Construction of Sandwich-Type Double-[1 + 1] and Half-Folded [2 + 2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects.

The first-row transition-metal ions Mn2+-Cu2+ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn2+-Cu2+ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co2+ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H2pdd precursor and the [1 + 1] Cu2+ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H2hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.