Central Metal Atom Research Articles

Synthesis and Characterization of Zr and Hf Triazenido Complexes with Rare κ1N-Coordination Built Directly in the Coordination Sphere of the Metal

The synthesis and characterization of triazenido complexes of the group IV metals zirconium and hafnium is reported. The reaction of the group IV pentafulvene complexes Cp*(π–η5:σ–η1-pentafulvene)-zirconium(IV) and -hafnium(IV)chlorides with the sterically demanding 2,6-dimesitylphenyl azide results in the insertion of the γ-nitrogen atom of the ligand precursor into the polarized M–Cexo (Cexo: exocyclic carbon atom) bond of the pentafulvene ligand, forming a formal Cp,N,N tridentate ligand system. The molecular structures of the furnished complexes reveal the rare κ1N coordination of the γ-nitrogen atom to the zirconium or hafnium center along with a localized Nα–Nβ double bond. Unusually, in one case, the ligand system shows additional coordination of the α-nitrogen atom to the central metal atom and well-balanced N–N distances, thus, forming the chelating κ2N,N coordination mode of the triazenido ligand. The potential use of the formed complexes as precursors for cationic group IV cationic complexes was investigated by reaction with methyl lithium.

Magnetic coupling between Fe(NO) spin probe ligands through diamagnetic NiII, PdII and PtII tetrathiolate bridges.

Reaction of the nitrosylated-iron metallodithiolate ligand, paramagnetic (NO)Fe(N2S2), with [M(CH3CN)n][BF4]2 salts (M = NiII, PdII, and PtII; n = 4 or 6) affords di-radical tri-metallic complexes in a stairstep type arrangement ([FeMFe]2+, M = Ni, Pd, and Pt), with the central group 10 metal held in a MS4 square plane. These isostructural compounds have nearly identical ν(NO) stretching values, isomer shifts, and electrochemical properties, but vary in their magnetic properties. Despite the intramolecular Fe⋯Fe distances of ca. 6 Å, antiferromagnetic coupling is observed between {Fe(NO)}7 units as established by magnetic susceptibility, EPR, and DFT studies. The superexchange interaction through the thiolate sulfur and central metal atoms is on the order of NiII < PdII ≪ PtII with exchange coupling constants (J) of -3, -23, and -124 cm-1, consistent with increased covalency of the M-S bonds (3d < 4d < 5d). This trend is reproduced by DFT calculations with molecular orbital analysis providing insight into the origin of the enhancement in the exchange interaction. Specifically, the magnitude of the exchange interaction correlates surprisingly well with the energy difference between the HOMO and HOMO-1 orbitals of the triplet states, which is reflected in the central metal's contribution to these orbitals. These results demonstrate the ability of sulfur-dense metallodithiolate ligands to engender strong magnetic communication by virtue of their enhanced covalency and polarizability.

Chiral metallic anticancer drugs: A brief-review

Chiral metallic drugs are becoming the hottest point of discussion in the field of medicinal chemistry. As we know that more than 80% drugs are chiral in nature, and prescribed in the racemic form. The main problem with chiral drugs is the different biological activities of different enantiomers. This is because the human body has a chiral environment, as there is the presence of protein, carbohydrates, enzymes, and other chiral macromolecules. Hence, if a chiral anticancer drug is being prescribed to the patient in the racemic form, it means two or more drugs are being prescribed. Therefore, the chiral separation and analysis of chiral anticancer drugs are important for improving the quality of chiral drug medication. Many metal complexes are used as anticancer drugs, but the conditions become more critical if they have chirality or a chiral moiety, because of which they exist in two or more forms. Because of the presence of chirality or chiral moiety, the complex of metals is termed a chiral metallic complex. Of course, the enantioseparation of the chiral metallic complexes must be done before their prescription. Enantioseparation of the chiral metallic complex will not only provide a pharmaceutically active form to the patient but also reduce the side effects caused by the racemic mixture. Hence, the accessible article reviews the chiral metallic complexes having ruthenium, osmium, palladium, gold, silver, and platinum, etc. as central metal atoms. Besides, the future perspectives regarding the chiral metallic anticancer drugs and the role of their enantioseparation are also discussed.

Boosting the oxygen reduction reaction behaviour of Ru single atoms in porous carbon nanospheres via microscopic coordination environment manipulation

The development of high-performing oxygen reduction reaction (ORR) single atom catalysts (SACs) is the basis for mass production of metal-air batteries and fuel cells. This is also an important means to achieve peak carbon dioxide emissions and carbon neutrality. Ru SACs can effectively imped Fenton reactions and significantly enhance resistance to attenuation. However, Ru SACs exhibit inferior ORR activity than TM (transition metal)-N-C catalysts and Ru atoms are prone to agglomeration. Herein, we report a simple method for the controllable preparation of Ru SAs in N and S modulated porous carbon nanospheres (Ru-SAs-N/S-PCNSs). S heteroatoms doping can change the charge density of Ru central metal atom, and reduce its binding strength to ORR intermediates, and expedite ORR activity. The porous carbon nanospheres matrix makes Ru SAs active site fully exposed. The onset potential and half-wave potential of Ru-SAs-N/S-PCNSs electrocatalyst is as high as 1.0 V and 0.87 V (vs RHE), which is in the excellent ranks. In addition, the performance of Zn-air battery with Ru-SAs-N/S-PCNSs is better than that of Pt/C + RuO2. The synthesis method we developed can effectively preclude the agglomeration of Ru metal atoms, and provides a new pathway for the preparation of SACs with high catalytic performance.

Surface bonding of MN4 macrocyclic metal complexes with pyridine-functionalized multi-walled carbon nanotubes for non-aqueous Li-O2 batteries

It is essential to develop bifunctional catalysts with high activity and stability for reversible oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) in lithium-oxygen (Li-O2) batteries. In this work, pyridine (Py) functionalized multi-walled carbon nanotubes (MWCNTs) were prepared to immobilize various solid MN4 macrocyclic metal complexes (MN4-MC) as cathode electrocatalysts for Li-O2 batteries. Three types of MN4-MC molecules, including iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc) and iron protoporphyrin IX (Heme) were examined to evaluate the influence of central metal atoms and ligand substituents found in MN4-MC molecules on the electrocatalytic performance of the study samples. The order of the ORR/OER catalytic activity of the bifunctional catalysts is FePc > Heme > CoPc. The central metal atom in FePc molecule has the highest occupied molecular orbital (HOMO) energy than the corresponding metal atoms in CoPc and Heme molecules. This made the molecule to have better dioxygen-binding ability and higher catalytic activity in the ORR process; it also made it to easily lose electrons that were oxidized in the OER process. This study proposed a simplified scheme of the electrode surface route to assist in understanding the diverse ORR/OER performances of MN4-MC. It is discovered that the positive core of the MN5 coordination sphere in MN4-MC/Py/MWCNTs composite is the primary active site that can influence the formation of MN5···O2* and MN5-LOOLi cluster in the ORR process. The interfacial electron could be easily delivered between MWCNTs and MN5 active site through the Py bridge. This facilitated the formation and decomposition of MN5-LOOLi species during the ORRs/OERs, leading to the enhancement of its catalytic performance. This work provides a new insight into the effects of the molecular structure and organization of MN4-MC on the catalytic activity of O2 electrodes in Li-O2 batteries.

Investigation of Non-Isothermal Curing of an Epoxy Resin with Partially Substituted Polyethoxymetallosiloxanes

Differential scanning calorimetry is used to study the curing of an epoxy resin with metal organosiloxanes differing in the type of a central metal atom (Al, Zr). The equilibrium temperatures and apparent activation energies of curing reactions are defined. It is established that the type of the central metal atom predetermines the thermal effect of the curing reaction and the activity of the metal organosiloxane as an epoxy resin curing agent.

Olefin coordination versus weak agostic C[sbnd]H[sbnd]M interactions in Sandwich-Type complexes of the split (3 + 2) Five-Electron donor hydrocarbon ligand Tricyclo[5.2.1.0]-deca-3,8-dien-5-yl (dicp) related to cyclopentadiene dimer

Sandwich-type complexes (dicp)MCp (M = Ti, V, Cr, Mn, Fe, Co, Ni; Cp = cyclopentadienyl) of the split (3 + 2) five-electron donor ligand tricyclo[5.2.1.0]-deca-3,8-dien-5-yl (dicp) related to cyclopentadiene dimer have been investigated by density functional theory. In the low-energy structures of the transition metal complexes (dicp)MCp (M = Ti, V, Cr, Mn, Fe), all of the split (3 + 2) five electrons from the dicp ligand are donated to the central transition metal atom leading to 14-, 15-, 16-, 17, and 18-electron configurations for the singlet (dicp)TiCp, quartet (dicp)VCp, triplet (dicp)CrCp, doublet (dicp)MnCp, and singlet (dicp)FeCp structures. For the late transition metals Co and Ni, only the allyl unit of the dicp ligand is strongly coordinated to the transition metal atom, in contrast to the Cp2Co and Cp2Ni in which all ten carbon atoms of the two cyclopentadienyl ligands are coordinated to the central metal atom. The potential energy surface for the manganese complex (dicp)MnCp is much more complicated than that of manganocene Cp2Mn, in which the doublet, quartet, and sextet structures are nearly degenerate in energy, with the quartet and sextet low-energy structures having only have part of the allyl or olefin unit coordinated to the central manganese atom. Weak agostic CHM interactions between the dicp ligand and the metal atoms, typically with M—H distances of ∼2.7 Å, are found in many of the (dicp)MCp complexes in contrast to the Cp2M (M = Ti, V, Cr, Mn, Fe, Co, Ni).

Robust broken-gap MoTe2/ZrS2 van der Waals heterostructure

Two-dimensional van der Waals (vdW) heterostructures with several possibilities of band edge alignment are promising candidates in the design of semiconductor junction devices with good electrostatic control. We predict a robust broken-gap band alignment for the ${\mathrm{MoTe}}_{2}/{\mathrm{ZrS}}_{2}$ vdW heterostructure and uncover the underlying mechanism. Our first-principles calculations reveal that upon formation of the vdW heterostructure a small amount of charge is transferred between the layers which sits on the central transition metal atoms and is responsible for the band edge alignment. Moreover, the lattice-mismatch-induced in-plane strain and the interfacial polarization are shown to play no role in band alignment. However, we find a weak sensitivity of the electronic structure and band edge alignment of the vdW heterostructures to an external normal-to-plane strain or electric field. Our findings are helpful in designing heterojunction devices with desired electronic structures.

Synthesis, Spectroscopic Characterization, Biocidal evaluation Molecular Docking & DFT Investigation of 16-18 membered Macrocyclic Complexes of Cobalt (II).

Antimicrobial, DFT, and Docking representation of Cobalt (II) macrocyclic complexes. The online version contains supplementary material available at 10.1007/s12039-022-02109-2.

Tuning the Coordination Microenvironment of Central Fe Active Site to Boost Water Electrolysis and Oxygen Reduction Activity.

In heterogeneous catalysis, single-atom catalysts are the frontier and important prototypes for many reactions, and revealing the intrinsic structure-activity relationship is presently a critical task, but remains challenging. In this work, water electrolysis and oxygen reduction performances of FeXYi N3 -i (X, Y = B, C, O, P and S; i= 0, 1) moiety in Fe-porphyrin are studied by the first-principles calculations, aiming at unraveling how and why tuning the coordination microenvironment of the active metal atom can improve the activity. It can be concluded that breaking the coordination shell symmetry breaks the well-accepted standard scaling relationship, adjusts *O adsorption behavior and thus optimizes the oxygen evolution reaction (OER) activity, for example, to an extremely low overpotential of 0.17V. In combination with the Fe atom spin configuration and ligand field theory, the dramatically improved OER activity can be well explained. In the present work, the significance of the coordination microenvironment of central metal atom in studies of electrocatalysis is highlighted.

Influence of central atoms on the catalytic effect of transition metal phthalocyanines in Li-S battery cathodes

Transition metal phthalocyanines (MPc) with different central metal atoms of Co(II), Fe(II), Ni(II), Mn(II) and Cu(II) were loaded on carbon nanofibers to act as the cathode catalytic materials for Li-S batteries. The influence of central atoms on the catalytic activity was explored. Higher specific capacities and cycling stability were achieved with CoPc and FePc, exhibiting higher catalytic activities for the oxidation and reduction processes respectively. The MPc molecules all present similar adsorption geometries with Li2S6 and adsorption energy was found to be unsuitable to explain the difference. The presence of unoccupied dz2 orbitals in Co and Fe might be the origin for the higher catalytic activities.

Engineering the Coordination Interface of Isolated Co Atomic Sites Anchored on N-Doped Carbon for Effective Hydrogen Evolution Reaction.

The regulation of the coordination environment of the central metal atom is considered as an alternative way to enhance the performance of single-atom catalysts (SACs). Herein, we design an electrocatalyst with active sites of isolated Co atoms coordinated with four sulfur atoms supported on N-doped carbon frameworks (Co1-S4/NC), confirmed by high-angle annular dark-field scanning transmission electron microscope (HADDF-STEM) and synchrotron-radiation-based X-ray absorption fine structure (XAFS) spectroscopy. The Co1-S4/NC possesses higher hydrogen evolution reaction (HER) catalytic activity than other Co species and exceptional stability, which exhibits a small Tafel slope of 60 mV dec-1 and a low overpotential of 114 mV at 10 mA cm-2 during the HER in 0.5 M H2SO4 solution. Furthermore, through in situ X-ray absorption spectrum tests and density functional theory (DFT) calculations, we reveal the catalytic mechanism of Co1-S4 moieties and find that the increasing number of sulfur atoms in the Co coordination environment leads to a substantial reduction of the theoretical HER overpotential. This work may point a new direction for the synthesis, performance regulation, and practical application of single-metal-atom catalysts.

Microenvironment Modulation in Carbon‐Supported Single‐Atom Catalysts for Efficient Electrocatalytic CO2 Reduction

The electrocatalytic CO2 reduction reaction (ECRR) becomes an effective way to reduce excess CO2 in the air and a promising strategy to maintain carbon balance. Carbon-supported single-atom catalysts (C-SACs) is a kind of cost savings and most promising catalysts for ECRR. For C-SACs, the key to achieving efficient ECRR performance is to adjusting the electronic structure of the central metal atoms by modulating their microenvironment of the catalysts. Not only the coordination numbers and hetero-atom coordination, but also the regulation of diatomic sites have a great influence on the performance of C-SACs. This review mainly focuses on recent studies for the microenvironment modulation in C-SACs for efficient ECRR. We hope that this review can contribute readers a comprehensive insight in the current research status of C-SACs for ECRR, as well as provide help for the rational design of C-SACs with better ECRR performance.

Potential risk resulting from the influence of static magnetic field upon living organisms. Numerically simulated effects of the static magnetic field upon metalloporphyrines

Background: An attempt to recognize the effects of a static magnetic field (SMF) of varying flux density on flora and fauna.. For this purpose the influence of static magnetic field upon molecules of Mg(II), Fe(II), Fe(III), Co(II), Co(III) and Cu(II) metalloporphyrins is studied. Methods: Computations of the effect of real SMF 0.0, 0.1, 1, 10 and 100 AFU (Arbitrary Magnetic Field Unit; here 1AMFU &amp;gt; 1000 T) flux density were performed in silico (computer vacuum) involving advanced computational methods. Results: The static magnetic field (SMF) decreased the stability of the metalloporphyrine molecules. This effect depended on the situation of the molecule in respect to the direction of the SMF of the Cartesian system. An increase in the value of heat of formation was accompanied by an increase in the dipole moment. It was an effect of deformations of the molecule which involved pyrrole rings holding the hydrogen atoms at the ring nitrogen atoms and the length of the C-H and N-H bonds. As a consequence, that macrocyclic ring lost its planarity. Conclusions: SMF even of the lowest, 0.1 AMFU flux density influences the biological role of metalloporphyrines associated with their central metal atoms. This effect is generated by changes in the electron density at these atoms, its steric hindering and polarization of particular bonds from pure valence bonds possibly into ionic bonds.

Chemical Vapor Deposition of High-Optical-Quality Large-Area Monolayer Janus Transition Metal Dichalcogenides.

One-pot chemical vapor deposition (CVD) growth of large-area Janus SeMoS monolayers is reported, with the asymmetric top (Se) and bottom (S) chalcogen atomic planes with respect to the central transition metal (Mo) atoms. The formation of these 2D semiconductor monolayers takes place upon the thermodynamic-equilibrium-driven exchange of the bottom Se atoms of the initially grown MoSe2 single crystals on gold foils with S atoms. The growth process is characterized by complementary experimental techniques including Raman and X-ray photoelectron spectroscopy, transmission electron microscopy, and the growth mechanisms are rationalized by first principle calculations. The remarkably high optical quality of the synthesized Janus monolayers is demonstrated by optical and magneto-optical measurements which reveal the strong exciton-phonon coupling and enable an exciton g-factor of -3.3.

Influence of the molecular structure of metal-phthalocyanine on electrocatalytic reactions

The demand for new catalysts for renewable energy production has become crucial. As an alternative to metal catalysts for electrocatalysis to produce energy sources, metal-phthalocyanine (MPc) electrocatalysts have shown potential. Their physicochemical and electrochemical properties depend on the chemical structure of the MPc and the central metal atom. Recent reviews of MPcs focused on their electrochemical performance in specific catalytic reactions, such as oxygen reduction reaction and CO2 reduction reaction. However, understanding the structure of MPcs in depth is important, since their electrochemical catalytic activity is affected by structural modifications of MPcs. Therefore, this minireview focuses on how the molecular structure of MPcs affects electrochemical catalysis.

Modulating the microenvironment structure of single Zn atom: ZnN4P/C active site for boosted oxygen reduction reaction

The electronic structure of catalytic active sites can be influenced by modulating the coordination bonding of the central single metal atom, but it is difficult to achieve. Herein, we reported the single Zn-atom incorporated dual doped P, N carbon framework (Zn-N4P/C) for ORR via engineering the surrounding coordination environment of active centers. The Zn-N4P/C catalyst exhibited comparable ORR activity (E1/2 = 0.86 V) and significantly better ORR stability than that of Pt/C catalyst. It also shows respectable performance in terms of maximum peak power density (249.6 mW cm−2), specific capacitance (779 mAh g−1), and charge-discharge cycling stability for 150 hours in Zn-air battery. The high catalytic activity is attributed to the uniform active sites, tunable electronic/geometric configuration, optimized intrinsic activity, and faster mass transfer during ORR-pathway. Further, theoretical results exposed that the Zn-N4P configuration is more electrochemically active as compared to Zn-N4 structure for the oxygen reduction reaction.

Benchmarking the two-dimensional conductive Y3(C6X6)2 (Y = Co, Cu, Pd, Pt; X = NH, NHS, S) metal-organic framework nanosheets for CO2 reduction reaction with tunable performance

Scrutinizing competent and economical electrocatalysts for carbon-di-oxide reduction reactions (CO2RR) is essential for wide-range commercialization of livestock feed. Therefore, via density functional theory (DFT), we broadly explored the electrocatalytic performance of two-dimensional (2D) metal−organic frameworks (Y3(C6X6)2), where Y indicates Co, Cu, Pd, Pt; and X indicates organic ligands; (NH, NHS, S) for CO2RR. The 2D Y3(C6X6)2 monolayers unveiled metallic behavior due to the suitable π electron conjugation network and the productive interaction among the metal atom, organic ligands, and benzene rings, except for Co3(C6S6)2, which revealed semiconducting behavior. Significantly, the catalytic performance of Y3(C6X6)2 is influenced by the strength of interaction between the CO2RR intermediates and the metal complex (Y-X4), which may be altered by varying the central metal atom with different d-electron orbitals or by organic ligands. Surprisingly, Co3(C6(NH)3S3)2, Co3(C6(NH)3)2, and Cu3(C6S6)2 have excellent CO2RR to formic acid activity. Whereas, Pt3(C6(NH)3)2 and Pd3(C6(NH)3)2 shows good CO2RR to carbon mono-oxide activity. Our research provides imperative insights for designing and screening efficient CO2RR catalysts. This research put forward the idea of developing metal-organic frameworks with beneficial properties to meet the specific requirements of diverse research areas, such as catalysis, energy storage, and molecular sensing.

Variable Learning‐Memory Behavior from π‐Conjugated Ligand to Ligand‐Containing Cobalt(II) Complex†

Comprehensive SummaryIn the information‐explosion era, developing novel algorithms and memristive devices has become a promising concept for next‐generation capacity enlargement technology. Organic small molecule‐based devices displaying superior learning‐memory performance have attracted much attention, except for the existence of poor heat‐resilience and mediocre conductivity. In this paper, a strategy of transforming an organic‐type data‐storage material to metal complex is proposed to resolve these intrinsic issues. A pristine NDI‐derivative (NIPy) and its corresponding Co(II) complex (CoNIPy) are synthesized for the purpose of electrical property investigation. CoNIPy complex‐based memristive device exhibits superior ternary WORM memory performance compared with the binary behavior of NIPy, including &gt;104 s of reading, lower threshold voltage (Vth), 1: 102: 105 of OFF/ON1/ON2 current ratio, and long‐term stability in heating environment. The variable learning‐memory behavior can be attributed to the enhanced ligand‐to‐metal charge transfer (LMCT) and improved redox activity after the introduction of central metal atom and coordination bond. These studies on material innovation and optimal performance are of great importance not only for environmentally‐robust memristive devices but also for practical application of a host of organic electronic devices.

(Invited) Nucleation and Growth of Small Atomic Aggregates into Superatom Nanoclusters

One of the challenges in nucleation and growth of small atomic aggregates is to develop the novel research field of solid-state chemistry and material science using gas-phase-synthesized superatom nanoclusters. Among various superatoms, the greatest advantage of the central-atom-encapsulating binary superatoms, such as M@Si16, is that their electronic structures can be designed by optimizing the central metal atom M while retaining the geometrical symmetry of the Si16 cage [1], as shown in the figure below. We have systematically investigated the nucleation and growth of M@Si16 superatoms with gas-phase mass spectrometry, and then performed the surface immobilization of the M@Si16 cations and anions on a substrate monodispersively with the size-selective soft-landing. Initial products prepared via the surface immobilization of M@Si16 superatoms on solid surfaces decorated with monolayer films of C60 molecules were investigated using scanning tunneling microscopy (STM) [2] and X-ray photoelectron spectroscopy (XPS) [3]. Furthermore, we have developed a large-scale synthesis method for M@Si16 (M = Ti and Ta) by scaling up the clean dry-process with a high-power impulse magnetron sputtering (HiPIMS, nanojima®) [4] and by a direct liquid embedded trapping (DiLET) method [5]. The spectroscopic results reveal that the structures of soft-landed and isolated M@Si16 superatoms are the metal-encapsulating tetrahedral silicon-cage (METS) [5,6].Furthermore, superatoms of group-5 metals (M = V, Nb, and Ta) encapsulating Si16 cage nanoclusters (M@Si16) can be efficiently generated to form assembled films [7]. Temperature-dependent current–voltage (I–V) characteristics of the M@Si16 assembled films revealed that the electrical conduction mechanism is not band transport, but hopping transport with Efros–Shklovskii variable range hopping for all central M atoms [8]. The results show that electrons involved in conduction are strongly correlated to localized electronic states.[1] K. Koyasu, A. Nakajima, et al. J. Am. Chem. Soc. 127, 4998 (2005).[2] M. Nakaya, A. Nakajima, et al. Nanoscale, 6, 14702 (2014).[3] M. Shibuta, A. Nakajima, et al. J. Am. Chem. Soc. 137, 14015 (2015).[4] C. H. Zhang, A. Nakajima, et al. J. Phys. Chem. A 117, 10211 (2013).[5] H. Tsunoyama, A. Nakajima, et al. J. Phys. Chem. C 121, 20507 (2017).[6] H. Tsunoyama, A. Nakajima, et al. Acc. Chem. Res. 51, 1735 (2018).[7] M. Shibuta, A. Nakajima, et al. J. Phys. Chem. C, 124, 28108 (2020).[8] T. Yokoyama, A. Nakajima, et al. J. Phys. Chem. C, 125, 18420 (2021). Figure 1