Metal Coordination Environment Research Articles

Pressure-induced phase transitions of cobalt sulfate hydrates and discovery of a new high-pressure phase, CoSO4·5H2O

Pressure-induced dehydration transitions of CoSO4·6H2O and CoSO4·7H2O were observed by in-situ powder X-ray diffraction at high pressure. Both transformed to an unreported high-pressure phase, CoSO4·5H2O at 1–2 ​GPa, whose crystal structure was determined by single crystal X-ray diffraction. The results show that CoSO4·5H2O has a triclinic structure with cell parameters of a ​= ​6.4436 (6) Å, b ​= ​10.2300 (12) Å, c ​= ​5.1914 (6) Å, α ​= ​91.953 (10)°, β ​= ​87.084 (10)°, γ ​= ​101.085 (10)°, V ​= ​335.28 (6) Å3, at 1.3 ​GPa, and it has a layered crystal structure consisting of [Co(H2O)6] and [Co(H2O)4(SO4)2]. This structure is distinct from previously reported crystal structures of MSO4·5H2O (M ​= ​Mg, Mn, Fe, Cu) in a metal coordination environment. The compressibility of CoSO4·5H2O was fitted by the 3rd-order Birch-Murnaghan equation of state, yielding K0 ​= ​25 (±2) GPa, K0′ ​= ​7.4 (±0.5), V0 ​= ​352 (±2) Å3.

4-hydroxyphenylpyruvate dioxygenase (HPPD)における金属活性中心の力場パラメータの構築とその評価

Metalloproteins such as 4-hydroxyphenylpyruvate dioxygenase (HPPD) and Cytochrome P450 are important for agrochemical research. In classical mechanics, to reproduce the metal-coordination environment of metalloproteins, various models (Nonbonded model, Bonded model, Nonbonded/Bonded Hybrid model etc.) for metal complexes have been developed. In this study, we built force field parameters for the molecular dynamics simulation of HPPD and evaluated the Fe2+-coordination environment. The result revealed that the hybrid model is suitable for the simulation of HPPD and able to simulate the metal-ligand (water) exchange process.

Rational construction of thermally stable single atom catalysts: From atomic structure to practical applications

As a new frontier in catalysis field, single-atom catalysts (SACs) hold unique electronic structure and high atom utilization, which have displayed unprecedented activity and selectivity toward a wide range of catalytic reactions. However, many reported SACs are susceptible to Ostwald ripening process in high temperature environment or long-term catalytic application, which will cause sintering and deactivation. This is due to the weak interaction between the metal atom and supports. The regeneration and recycling of deactivated catalysts will greatly increase the time and economic cost of industrial production. Therefore, it is necessary to develop SACs with excellent thermal stability to meet the industrial demands. Here, we discuss the fundamental comprehension of the stability of thermally stable SACs obtained from different synthesis methods. The influences of the speciation of metal centers and coordination environments on thermal stability are summarized. The importance of using novel in situ and operando characterizations to reveal dynamic structural evolution under synthesis and reaction conditions and to identify active sites of thermally stable SACs is highlighted. The mechanistic understanding of the unique role of thermally stable SACs in thermocatalytic application is also discussed. At last, a brief perspective on the remaining challenges and future directions of thermally stable SACs is presented.

Electronics and coordination engineering of atomic cobalt trapped by oxygen-driven defects for efficient cathode in solar cells

A rational design and the metal coordination environment regulating of single-atom catalysts (SACs) in specific catalytic reaction remain great challenges. The oxygen defective support can be employed as traps to capture metal species, which provides an effective pathway to synthesize SACs. Here, we propose a counterions-assisted oxygen-driven defect capture (CODC) strategy to fabricate a series of atomically dispersed Co-based catalysts with different electronic and coordination environments. When serving as cathode for dye-sensitized solar cells (DSCs), the triiodine reduction reaction (IRR) activity is very sensitive to the coordination structure. Density functional theory (DFT) calculations reveal that the intrinsic electronic distributions, electron-donating ability, and energy level position determine the coordination behavior and catalytic performance of SACs. Our findings not only define an efficient synthetic strategy to a broad class of M-N x C y based SACs for highly-efficient IRR, but also provide an insight for exploring coordination-sensitive reaction from the atomic view. • An electronic and coordination environment control for accelerating the IRR process was developed. • The atomically dispersed Co-based catalysts were synthesized by a counterions-assisted oxygen-driven defect capture strategy. • The IRR catalytic activity was sensitive to the coordination structure of atomic cobalt. • The electron-donating ability and energy level position determined the coordination behavior of SACs by DFT study.

Ball-Milling Induced Debonding of Surface Atoms from Metal Bulk for Construing High-Performance Dual-Site Single-Atom Catalysts.

One of the most pressing challenges in single-atom catalysis is the manipulation of the coordination environment of central metals to maximize the catalyst performance. Herein, we fabricated a high-performance catalyst (Co-SNC) by introducing S into the neighboring position of the Co-N4 coordination. The developed ball-milling method enabled large-scale synthesis, that over 4.7 g of Co-SNC can be produced in one pot. In benzylamine coupling reaction, Co-SNC exhibited the highest conversion of 97.5 % with 99 % selectivity toward N-benzylidenebenzylamine in 10 h among various Co catalysts. Density functional theory calculations revealed the crucial role of S atoms, which serve as the active sites for O2 activation, leaving the Co atoms free to adsorb benzylamine. Consequently, the adsorption energies of O2 and benzylamine were significantly increased. Our strategy suggests a feasible approach to enhance catalytic performance by delicately integrating dual active sites into a single catalyst unit.

Ball‐Milling Induced Debonding of Surface Atoms from Metal Bulk for Construing High‐Performance Dual‐Site Single‐Atom Catalysts

AbstractOne of the most pressing challenges in single‐atom catalysis is the manipulation of the coordination environment of central metals to maximize the catalyst performance. Herein, we fabricated a high‐performance catalyst (Co‐SNC) by introducing S into the neighboring position of the Co‐N4 coordination. The developed ball‐milling method enabled large‐scale synthesis, that over 4.7 g of Co‐SNC can be produced in one pot. In benzylamine coupling reaction, Co‐SNC exhibited the highest conversion of 97.5 % with 99 % selectivity toward N‐benzylidenebenzylamine in 10 h among various Co catalysts. Density functional theory calculations revealed the crucial role of S atoms, which serve as the active sites for O2 activation, leaving the Co atoms free to adsorb benzylamine. Consequently, the adsorption energies of O2 and benzylamine were significantly increased. Our strategy suggests a feasible approach to enhance catalytic performance by delicately integrating dual active sites into a single catalyst unit.

Role of metal center and coordination environment in M-(Z)-N-((E)-pyridin-2-ylmethylene)isonicotinohydrazonate (M = LaIII, ZnII, CdII or HgII) catalyzed cyanosilylation of aldehydes

A series of known metal complexes, [LaL2(NO3)(H2O)2]·5H2O (1), [Zn(μ-L)(NO3)(H2O)]n (2), {[Cd2(μ-HL)(μ-L)(NO3)3(H2O)]·H2O}n (3) and [Hg(μ-L)(N3)]n·nH2O (4), were synthesized from the corresponding metal salts and 2-pyridinecarboxaldehyde isonicotinoylhydrazone (HL), and demonstrated high activity and selectivity in the cyanosilylation of aldehydes. Although all the complexes are derived from the same HL hydrazone ligand, the catalytic activity of 1–4 is different and relates to the metal center and coordination environment, whereas complex 1 being the most effective homogeneous Lewis acid-base catalyst towards the synthesis of cyanohydrin trimethylsilyl ethers from both aliphatic and aromatic aldehydes with yields up to 96.3 % in 6 h in methanol solution and at room temperature. According to the proposed mechanism, both coordination and noncovalent interactions (hydrogen and tetrel bonds) play a significant role and account for the higher catalytic activity of complex 1.

Intrinsic Descriptors for Coordination Environment and Synergistic Effects of Metal and Environment in Single-Atom-Catalyzed Carbon Dioxide Electroreduction

Activity of heterogeneous single-atom catalysts (SACs) depends on both the active center and the coordination environment. Previous studies focus more on the former. In this study, we systematically examine CO2 reduction reaction (CO2RR) catalyzed by SACs with different coordination environments on graphene. We find that carbon and nitride coordination generally leads to higher activity compared to phosphorus and sulfur coordination. C, N-rich environment is more likely to produce CO, while P, S-rich environment prefers HCOOH production. Two intrinsic descriptors, namely, average number of electrons in outer p-orbitals and average third ionization energy, are identified to describe coordination environment. Furthermore, two intrinsic descriptors are proposed to describe the synergistic effects of metal active center and coordination environment. By checking available data in the literature, we confirm that these descriptors are quite universal for CO2RR. Part of them is even suitable for oxygen reduction reaction (ORR). This study opens a new avenue to screen high performance SACs based on intrinsic properties of the metal and environmental elements.

Reversible Ligand Exchange in Atomically Dispersed Catalysts for Modulating the Activity and Selectivity of the Oxygen Reduction Reaction.

Rational control of the coordination environment of atomically dispersed catalysts is pivotal to achieve desirable catalytic reactivity. We report the reversible control of coordination structure in atomically dispersed electrocatalysts via ligand exchange reactions to reversibly modulate their reactivity for oxygen reduction reaction (ORR). The CO-ligated atomically dispersed Rh catalyst exhibited ca. 30-fold higher ORR activity than the NHx -ligated catalyst, whereas the latter showed three times higher H2 O2 selectivity than the former. Post-treatments of the catalysts with CO or NH3 allowed the reversible exchange of CO and NHx ligands, which reversibly tuned oxidation state of metal centers and their ORR activity and selectivity. DFT calculations revealed that more reduced oxidation state of CO-ligated Rh site could further stabilize the *OOH intermediate, facilitating the two- and four-electron pathway ORR. The reversible ligand exchange reactions were generalized to Ir- and Pt-based catalysts.

Controllable modification for adjacent circumstance controls cellulose conversion to ketols on Ni CCCs at particle levels

The metal immobilizing micro-circumstance is intensively relevant to its catalytic activity and selectivity. In order to obtain C3,4 ketols by protection of C = O bonds against further hydrogenation, we proposed a promising strategy to modify adjacent circumstance for nickel complexes carbide catalysts (CCCs). The Sn promoted nickel CCCs exhibited high selectivity for cellulose conversion to C3,4 ketols with the yield of 54.8%. The characterization results demonstrated the coordination environment of metals were reconstructed by CxNy species to form isolated nickel sites. The size-dependent electron transfer occurred when the sizes changed (from cluster to nanoparticles). This electron transfer facilitated promotion of the selectivity for C3,4 ketols by protection of CO bonds against further hydrogenation. Combined with density functional theory calculations, the size-dependent electron transfer and Lewis base forming mechanism in Ni@CxNy structure were revealed. CxNy phases changed the electronic abundance of Ni sites and subsequently acted as Lewis base. Our work hinted that size of metallic catalysts should be optimized in specific loading circumstance to maximize the catalytic selectivity rather than simply chasing atomic efficiency.

1,2]‐Shift in Chiral Ni(II) Schiff‐Base Derivatives: Conversion of α‐ Thiobenzylated Amino Acid into the Cysteine Derivative

AbstractThe first example of the anionic [1,2]‐shift taking place in the metal coordination environment is described. The α‐thiobenzylated glycine in the form of the Ni(II) Schiff‐base complex is converted into the corresponding cysteine derivative with ca 70 % yield. The reaction disclosed emphasizes how the reactivity of a substrate can be influenced by noncovalent interactions in the metal coordination environment.

Carbon‐Supported Single‐Atom Catalysts: Carbon‐Supported Single Metal Site Catalysts for Electrochemical CO2 Reduction to CO and Beyond (Small 16/2021)

The carbon-supported single metal site catalysts have great potential for electrochemical CO2 reduction due to their flexibility to regulate metal centers, coordination environments, and local structures for enhancing catalytic activity and selectivity. Yi Mei, Gang Wu, and co-workers report that besides the high efficiency of CO2 to CO conversion, single metal sites could provide a synergy to design composite catalysts for producing other C2 products (article number 2005148).

New heptacoordinate tungsten(II) complexes with α-diimine ligands in the catalytic oxidation of multifunctional olefins

New tungsten(II) and molybdenum(II) heptacoordinate complexes [MX2(CO)3(LY)] (MXLy: M = W, Mo; X = Br, I; LY = C5H4NCY = N(CH2)2CH3 with Y = H (L1), Me (L2), Ph (L3)) were synthesized and characterized by spectroscopic techniques and elemental analysis. The two tungsten complexes WXL1 (X = Br, I) were also structurally characterized by single crystal X-ray diffraction. The metal coordination environment is in both a distorted capped octahedron. The complexes with L1 and L2 ligands were grafted in MCM-41, after functionalization of the ligands with a Si(OEt)3 group. The new materials were characterized by elemental analysis, N2 adsorption isotherms, 29Si MAS and 13C MAS NMR. The tungsten(II) complexes and materials were the first examples of this type reported. All complexes and materials were tested as homogeneous and heterogeneous catalysts in the oxidation of multifunctional olefins (cis-hex-3-en-1-ol, trans-hex-3-en-1-ol, geraniol, S-limonene, and 1-octene), with tert-butyl hydroperoxide (TBHP) as oxidant. The molybdenum(II) catalyst precursors are in general very active, reaching 99% conversion and 100% selectivity in the epoxidation of trans-hex-3-en-1-ol. Their performance is comparable with that of the [Mo(η3-C3H5)X(CO)2(LY)] complexes, but it increases with immobilization. On the other hand, most of the W(II) complexes display an activity similar or inferior to that of the Mo(II) analogues and it decreases after they are supported in MCM-41. DFT calculations show that tungsten complexes and iodide ligands are more easily oxidized from M(II) to M(VI) than molybdenum ones, while the energies of relevant species in the catalytic cycle are very similar for all complexes, making the theoretical rationalization of experimental catalytic data difficult.

Influence of the primary and secondary coordination spheres on nitric oxide adsorption and reactivity in cobalt(ii)-triazolate frameworks.

Nitric oxide (NO) is an important signaling molecule in biological systems, and as such, the ability of porous materials to reversibly adsorb NO is of interest for potential medical applications. Although certain metal–organic frameworks are known to bind NO reversibly at coordinatively unsaturated metal sites, the influence of the metal coordination environment on NO adsorption has not been studied in detail. Here, we examine NO adsorption in the frameworks Co2Cl2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) and Co2(OH)2(bbta) using gas adsorption, infrared spectroscopy, powder X-ray diffraction, and magnetometry. At room temperature, NO adsorbs reversibly in Co2Cl2(bbta) without electron transfer, with low temperature data supporting spin-crossover of the NO-bound cobalt(ii) centers of the material. In contrast, adsorption of low pressures of NO in Co2(OH)2(bbta) is accompanied by charge transfer from the cobalt(ii) centers to form a cobalt(iii)–NO− adduct, as supported by diffraction and infrared spectroscopy data. At higher pressures of NO, characterization data indicate additional uptake of the gas and disproportionation of the bound NO to form a cobalt(iii)–nitro (NO2−) species and N2O gas, a transformation that appears to be facilitated by secondary sphere hydrogen bonding interactions between the bound NO2− and framework hydroxo groups. These results provide a rare example of reductive NO binding in a cobalt-based metal–organic framework, and they demonstrate that NO uptake can be tuned by changing the primary and secondary coordination environment of the framework metal centers.

Intrinsic Activity of Metal Centers in Metal-Nitrogen-Carbon Single-Atom Catalysts for Hydrogen Peroxide Synthesis.

Metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) show high catalytic activity for many important chemical reactions. However, an understanding of their intrinsic catalytic activity remains ambiguous because of the lack of well-defined atomic structure control in current M-N-C SACs. Here, we use covalent organic framework SACs with an identical metal coordination environment as model catalysts to elucidate the intrinsic catalytic activity of various metal centers in M-N-C SACs. A pH-universal activity trend is discovered among six 3d transition metals for hydrogen peroxide (H2O2) synthesis, with Co having the highest catalytic activity. Using density functional calculations to access a total of 18 metal species, we demonstrate that the difference in the binding energy of O2* and HOOH* intermediates (EO2* - EHOOH*) on single metal centers is a reliable thermodynamic descriptor to predict the catalytic activity of the metal centers. The predicted high activity of Ir centers from the descriptor is further validated experimentally. This work suggests a class of structurally defined model catalysts and clear mechanistic principles for metal centers of M-N-C SACs in H2O2 synthesis, which may be further extendable to other reactions.

Rational Preparation of Atomically Precise Non-Alkyl Tin-Oxo Clusters with Theoretical to Experimental Insights into Electrocatalytic CO 2 Reduction Applications

Tin oxides (SnO2) have been widely utilized in electronics, nanolithography, and catalysis. As the atomically precise models of SnO2, tin-oxo clusters (TOCs) not only provide opportunities for mech...

Recent Advances in the Development of Single‐Atom Catalysts for Oxygen Electrocatalysis and Zinc–Air Batteries

AbstractRechargeable zinc–air batteries (ZABs) are presently attracting a lot of attention for electrical energy storage, owing to their low manufacturing cost and very high theoretical specific energy density. Currently, the large‐scale application of ZABs is hampered by the sluggish kinetics of the oxygen‐reduction reaction (ORR) and oxygen evolution reaction (OER), which underpin battery discharging and charging processes, respectively. In recent years, metal single‐atom catalysts (SACs) have emerged as promising candidates for driving oxygen electrocatalysis in ZABs, offering both high electrocatalytic activity and high metal atom utilization through unique metal coordination environments (typically porphyrin‐like MNx species on N‐doped carbon supports). Herein, recent breakthroughs in the design of SACs for ORR and OER electrocatalysis are summarized, with a general view towards improving ZAB performance. This Review begins by introducing the operating principles of ZABs and the reaction mechanisms of the ORR and the OER on the air electrode, after which the various types of SAC‐based materials developed to date for oxygen electrocatalysis and ZABs are discussed. Special emphasis is placed on the relationships between the structure of the SAC active site and electrocatalytic performance. Finally, challenges and opportunities for SACs in practical ZABs are explored.

Contributions of primary coordination ligands and importance of outer sphere interactions in UFsc, a de novo designed protein with high affinity for metal ions

Metalloproteins constitute nearly half of all proteins and catalyze some of the most complex chemical reactions. Recently, we reported a design of 4G-UFsc (Uno Ferro single chain), a single chain four-helical bundle with extraordinarily high (30 pM) affinity for zinc. We evaluated the contribution of different side chains to binding of Co(II), Ni(II), Zn(II) and Mn(II) using systematic mutagenesis of the amino acids that constitute the primary metal coordination and outer spheres. The binding affinity of proteins for metals was then measured using isothermal titration calorimetry. Our results show that both primary metal coordination environment and side chains in the outer sphere of UFsc are highly sensitive to even slight changes and can be adapted to binding different 3d metals, including hard-to-tightly bind metal ions such as Mn(II). The studies on the origins of tight metal binding will guide future metalloprotein design efforts.

Solid-state phase transformations toward a metal-organic framework of 7-connected Zn4O secondary building units

In the development of metal-organic frameworks (MOFs), secondary building units (SBUs) have been utilized as molecular modules for the construction of nanoporous materials with robust structures. Under solvothermal synthetic conditions, dynamic changes in the metal coordination environments and ligand coordination modes of SBUs determine the resultant product structures. Alternatively, MOF phases with new topologies can also be achieved by post-synthetic treatment of as-synthesized MOFs via the introduction of acidic or basic moieties that cause the simultaneous cleavage/reformation of coordination bonds in the solid state. In this sense, we studied the solid-state transformation of two ndc-based Zn-MOFs (ndc = 1,4-naphthalene dicarboxylate) with different SBUs but the same pcu topology to another MOF with sev topology. One of the chosen MOFs with pcu nets is [Zn2(ndc)2(bpy)]n (bpy = 4,4′-bipyridine), (6Cbpy-MOF) consisting of a 6-connected pillared-paddlewheel SBU, and the other is IRMOF-7 composed of 6-connected Zn4O(COO)6 SBUs and ndc. Upon post-structural modification, these pcu MOFs were converted into the same MOF with sev topology constructed from the uncommon 7-connected Zn4O(COO)7 SBU (7C-MOF). The appropriate post-synthetic conditions for the transformation of each SBUs were systematically examined. In addition, the effect of the pillar molecules in the pillared-paddlewheel MOFs on the topology conversion was studied in terms of the linker basicity, which determines the inertness during the solid-state phase transformation. This post-synthetic modification approach is expected to expand the available methods for designing and synthesizing MOFs with controlled topologies.

Isoreticular Linker Substitution in Conductive Metal–Organic Frameworks with Through‐Space Transport Pathways

AbstractThe extension of reticular chemistry concepts to electrically conductive three‐dimensional metal–organic frameworks (MOFs) has been challenging, particularly for cases in which strong interactions between electroactive linkers create the charge transport pathways. Here, we report the successful replacement of tetrathiafulvalene (TTF) with a nickel glyoximate core in a family of isostructural conductive MOFs with Mn2+, Zn2+, and Cd2+. Different coordination environments of the framework metals lead to variations in the linker stacking geometries and optical properties. Single‐crystal conductivity data are consistent with charge transport along the linker stacking direction, with conductivity values only slightly lower than those reported for the analogous TTF materials. These results serve as a case study demonstrating how reticular chemistry design principles can be extended to conductive frameworks with significant intermolecular contacts.