Multimetal Complexes Research Articles

Asymmetric by Design: Heteroleptic Coordination Compounds with Redox-Active Dithiolene and 1,2,4,5-Tetrakis(isopropylthio)benzene Ligands.

The 1,2,4,5-tetrakis(alkylthio)benzenes are redox-active organosulfur molecules that support oxidation to a stable radical cation. Their utility as ligands for the assembly of multimetal complexes with tailored functionality/property is unexamined. Here, 1,2,4,5-tetrakis(isopropylthio)benzene (tptbz, 1) is shown to bind PdCl2 at either one end, leaving the other open, or at both ends to form centrosymmetric [Cl2Pd(tptbz)PdCl2], 4. Ligand metathesis between Na2[(N≡C)2C2S2] (Na2mnt) and [Cl2M(tptbz)] (M = Pd, 2; M = Pt, 3) yields [(mnt)M(tptbz)] (M = Pd, 5; M = Pt, 6), but an alternative route involving transmetalation with [(mnt)SnMe2] delivers substantially greater yield. The mixed dithiolene-dithioether compound [(Ph2C2S2)Pt(tptbz)] (8) is formed by a similar transmetalation protocol using [(Ph2C2S2)SnnBu2]. Compounds 5, 6, and 8 are the first such heteroleptic complexes prepared by deliberate synthesis. The cyclic voltammetry of 8 reveals anodic waves at +0.14 and +0.97 V vs Fc+/Fc, which are attributed to successive dithiolene oxidation processes. While oxidized at +0.73 V as a free ligand, the redox-active MO of tptbz is pushed to a higher potential upon coordination to Pt2+ and is inaccessible. Calculations of the structures of [8]+ and of [((Cl2-3,5-C6H3)2C2S2)Pt(tptbz)]+ show that, in the latter, the dithiolene MOs are drawn down in energy into proximity with the tptbz MOs.

Metalloporphyrins: their multitalented nature as observed in multi-metal complex systems.

Five topics pertaining to the unique chemistry of metalloporphyrins as observed in multi-metal complex systems are introduced. The topics include the following: (i) the unique chromatographic separation of cyclic porphyrins on modified silica gel; (ii) room temperature phosphorescence from the zinc porphyrin part in a zinc porphyrin/rhenium complex hetero dyad; (iii) the substituent effect, in the preparation of a readily soluble special-pair-type zinc porphyrin dimer/rhenium complex having efficient photocatalytic CO2 reduction ability; (iv) assessment of the excited triplet state of a special-pair-type zinc porphyrin dimer in macrocyclic multiporphyrin rings; and (v) solvation/desolvation indicators based on exclusive transformation between the head-head type and head-tail type of supramolecular co-ordination polymers composed of bis(zinc porphyrin)s.

Theoretical study of the heterometal complexation of Pr(III) with L-isoleucine in the presence/absence of Mg(II) in solution: 4f-4f transition spectra as probe

The Judd-Ofelt intensity Tλ (λ=2, 4, 6), oscillator strength (P) and other energy interaction parameters like Slater Condon (FK), Racah (EK), Lande (ξ4f), nephelauxetic ratio (β), bonding (b1/2), percent covalency (δ) were evaluated to study the mode of interaction of Pr(III) with L-isoleucine in the presence/ absence of Mg(II) in different aquated organic solvents (DMF, dioxane, methanol and acetonitrile) and also at pH levels 2, 4, 6, using the 4f-4f transition spectra as a probe. The variation in values of both intensity and energy interaction parameters could reveal the formation of a bond among Pr(III), L-isoleucine, and Mg(II). Multimetal complexation among Pr(III) and the ligands were found to be most favourable in DMF solvent and at pH 6.

Covalent Organic Frameworks Composites Containing Bipyridine Metal Complex for Oxygen Evolution and Methane Conversion.

Novel covalent organic framework (COF) composites containing a bipyridine multimetal complex were designed and obtained via the coordination interaction between bipyridine groups and metal ions. The obtained Pt and polyoxometalate (POM)–loaded COF complex (POM–Pt@COF–TB) exhibited excellent oxidation of methane. In addition, the resultant Co/Fe–based COF composites achieved great performance in an electrocatalytic oxygen evolution reaction (OER). Compared with Co–modified COFs (Co@COF–TB), the optimized bimetallic modified COF composites (Co0.75Fe0.25@COF–TB) exhibited great performance for electrocatalytic OER activity, showing a lower overpotential of 331 mV at 10 mA cm−2. Meanwhile, Co0.75Fe0.25@COF–TB also possessed a great turnover frequency (TOF) value (0.119 s−1) at the overpotential of 330 mV, which exhibited high efficiency in the utilization of metal atoms and was better than that of many reported COF-based OER electrocatalysts. This work provides a new perspective for the future coordination of COFs with bimetallic or polymetallic ions, and broadens the application of COFs in methane conversion and electrocatalytic oxygen evolution.

Computational study of multimetal complexation of Nd(III) with GSH and Mg(II) in solution at different pH through 4f-4f transition spectra

Nd(III) complexes with GSH and Mg(II) have been studied using 4f-4f absorption spectrophotometry in different aquated organic solvents(50/50) in dioxane, methanol, acetonitrile and DMF. The mode of binding of Nd(III) with GSH and Mg(II) at pH 2, 4, 6 was also investigated. The binding behaviour of Nd(III) with GSH and Mg(II) along with the solvent and pH effect have been evaluated by using the computed energy interaction parameters like Slater-Condon (Fk, k = 2, 4, 6), Lande spin-orbit interaction (ξ4f), nephelauxetic ratio (β), bonding (b1/2) and percent covalency (δ).

A quantum chemical model for a series of self-assembled nanocages: the origin of stability behind the coordination-driven formation of transition metal complexes up to [M12L24]24.

Herein, we present a systematic computational model to study the electronic states and free energies of a self-assembled multi-metal complex series. By combining the previously developed model Hamiltonian approach for transition-metal complexes and the generalized Born model, the thermodynamics, optimized geometries, and electronic states of the [Pd12L24]24+ nanocage are revealed, together with [PdnLm]2n+ complex series. The effective model Hamiltonian is a theoretical method to obtain the d-electron wavefunction and potential energy including interaction energy between the transition-metal and ligands. In the present improvement, the electronic state on each transition-metal center is focused as a building unit and solved under the whole electronic field of the assembling system. We realize a reliable and systematic treatment of multi-transition-metal complexes with different sizes and charges. Consequently, our model could reproduce binding energies of the [PdnLm]2n+ complex series quantitatively as compared to density functional theory (DFT). Regarding free energy, we revealed that the assembling solute becomes unstable due to the electrostatic interaction, and effects of the solvent and counter anions mainly compensated it. Optimized geometries were also analysed. The local square-planar coordination structures around the palladium centres were characterized in the complex series. The relationships between the entire symmetrical geometries and the local coordination structures are also discussed. Finally, electronic structures of the [Pd12L24]24+ nanocage were well characterized as a single-determinant, where only dx2-y2 is unoccupied due to the ligand-field effect. We also found that the solvent polarized the electronic states of the Pd ions, whereas the counter anion suppressed the polarization. The present method realizes size-independent reliable and rapid computations, and therefore can be expected to further application studies on self-assembly dynamics.

Mechanistic insight to mycoremediation potential of a metal resistant fungal strain for removal of hazardous metals from multimetal pesticide matrix

Fungi have an exceptional capability to flourish in presence of heavy metals and pesticide. However, the mechanism of bioremediation of pesticide (lindane) and multimetal [mixture of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn)] by a fungus is little understood. In the present study, Aspergillus fumigatus, a filamentous fungus was found to accumulate heavy metals in the order [Zn(98%)>Pb(95%)>Cd(63%)>Cr(62%)>Ni(46%)>Cu(37%)] from a cocktail of 30 mg L−1 multimetal and lindane (30 mg L−1) in a composite media amended with 1% glucose. Particularly, Pb and Zn uptake was enhanced in presence of lindane. Remarkably, lindane was degraded to 1.92 ± 0.01 mg L−1 in 72 h which is below the permissible limit value (2.0 mg L−1) for the discharge of lindane into the aquatic bodies as prescribed by European Community legislation. The utilization of lindane as a cometabolite from the complex environment was evident by the phenomenal growth of the fungal pellet biomass (5.89 ± 0.03 g L−1) at 72 h with cube root growth constant of fungus (0.0211 g1/3 L−1/3 h−1) compared to the biomasses obtained in case of the biotic control as well as in presence of multimetal complex without lindane. The different analytical techniques revealed the various stress coping strategies adopted by A. fumigatus for multimetal uptake in the simultaneous presence of multimetal and pesticide. From the Transmission electron microscope coupled energy dispersive X-ray analysis (TEM-EDAX) results, uptake of the metals Cd, Cu and Pb in the cytoplasmic membrane and the accumulation of the metals Cr, Ni and Zn in the cytoplasm of the fungus were deduced. Fourier-transform infrared spectroscopy (FTIR) revealed involvement of carboxyl/amide group of fungal cell wall in metal chelation. Thus A. fumigatus exhibited biosorption and bioaccumulation as the mechanisms involved in detoxification of multimetals.

A new approach for the synthesis of electrocatalytically active CoFe2O4 catalyst for oxygen reduction reaction

Synthesis of non-precious electrocatalyst for the reduction of oxygen is of significant interest in the development of electrochemical energy conversion devices. Herein, we demonstrate a new, low-cost, and facile non-hydrothermal approach for the synthesis of electrocatalytically active spinel CoFe2O4 by thermal annealing of the multimetal complex, potassium cobalt hexacyanoferrate [K2CoFe(CN)6]. The as-synthesized CoFe2O4 is characterized by spectroscopic, electron microscopic and electrochemical techniques. The polyhedral-shaped crystalline CoFe2O4 particles have size ranging from 200 to 300nm. The CoFe2O4 catalyst is integrated with reduced graphene oxide (rGO) and its electrocatalytic activity toward oxygen reduction reaction is evaluated. The integrated hybrid catalyst rGO/CoFe2O4 favors the 4-electron reduction of oxygen to water at low overpotential in alkaline pH with Tafel slope of 63mV dec−1. The hybrid catalyst (rGO/CoFe2O4) has high durability and methanol tolerance. The catalytic performance is superior to that of the as-synthesized CoFe2O4 and rGO. The enhanced electrocatalytic performance is ascribed to the synergistic effect of CoFe2O4 and rGO, large surface area and high electronic conductivity. The ideal integration of CoFe2O4 with electronically conducting rGO favor the facile diffusion and promote the electron transfer for the reduction of oxygen.

Pressure-Leaching Behavior of Nickel from Ni–Mo Ore in Aqueous Oxygenated Media

AbstractNi–Mo ore is a multi-metal complex and unique mineral resource that exists as a black shale. This ore contains more than 4 wt% Mo and at least 2 wt% Ni. Economic value is associated with deriving products from Ni–Mo ore that contains amorphous colloidal sulfides and that is highly active. Under low-temperature hydrothermal conditions (water at 120 °C or more) and in excess oxygen, amorphous sulfides are oxidized easily to metal-sulfate forms, which leads to nickel and molybdenum dissolution. In this study, the effects of agitation speed, temperature, oxygen partial pressure and particle size on the rate of nickel leaching were investigated. The leaching rate was nearly independent of agitation speed above 400 rpm and increased with a decrease in particle size. A temperature increase to 150 °C contributed significantly to the nickel leaching rate. Oxygen pressure influences nickel leaching, with an oxygen pressure of between 0.5 MPa and 0.7 MPa providing the greatest effect. The pressure-leaching behavior of nickel was fitted to a shrinking-core kinetic model. The mathematical analyses indicates that the dissolution process is chemical-reaction controlled during early dissolution, with an activation energy of 42.68 kJ/mol, and the reaction order with respect to the oxygen partial pressure was 0.79. Up to nearly 70 % nickel was dissolved into solution, and product layers of molybdenum and iron oxide were formed on the surface of the Ni–Mo ore particles, which prevented further nickel dissolution. Thereafter, nickel leaching was controlled by liquid-film diffusion, with an activation energy of 11.01 kJ/mol.

Catalyst Support in Oxygen Electrocatalysis: A Case Study with CoFe Alloy Electrocatalyst

Synthesis of a highly efficient oxygen electrocatalyst is of significant interest for the development of energy storage devices. The electronic and surface structure, shape, size, and catalyst support largely control the electrocatalytic activity. We demonstrate the synthesis of bifunctional CoFe alloy electrocatalysts encased in nitrogen-doped graphitic carbon (N-C-CoFe) and supported on nitrogen-doped reduced graphene oxide (N-rGO-CoFe) for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) and the influence of catalyst support on the electrocatalytic performance. N-C-CoFe and N-rGO-CoFe were synthesized from a single-source precursor, potassium cobalt hexacyanoferrate multimetal complex, by thermal annealing. Both catalysts efficiently catalyze ORR and OER at low overpotential. The benchmark current density of 10 mA/cm2 for OER is obtained at very low overpotentials of 0.22 and 0.29 V with N-rGO-CoFe and N-C-CoFe, respectively. The N-C-CoFe catalyst is highly durable toward OER and...

Multi-metal citrate complex: green synthesis using Lime juice for hydrogen storage applications

Multi-metal citrate complex: green synthesis using Lime juice for hydrogen storage applications

Self-Assembly of Complex Multimetal Nanostructures from Perforated Lamellar Block Copolymer Thin Films.

We introduce a facile and effective fabrication of complex multimetallic nanostructures through block copolymer self-assembly. Two- and three-dimensional complex nanostructures, such as "nanomesh," "double-layered nanomeshes," and "surface parallel cylinders on nanomesh," can be fabricated using the self-assembly of perforated lamellar morphology in block copolymer thin films. Simultaneous integration of various metallic elements, including Pt, Au, and Co, into the self-assembled morphologies generates multimetal complex nanostructures with highly interconnected morphology and a large surface. The resultant metal nanostructures with a large surface area, robust electrical connectivity, and well-defined alloy composition demonstrate a high-performance electrochemical catalysis for hydrogen evolution reaction (current density: 6.27 mA/cm2@0.1 V and Tafel slope: 43 mV/dec).

Oxygen Electrocatalyst Based on Non-Precious Bifunctional Hybrid Material

Synthesis of new functional materials for the development of energy conversion and storage devices like fuel cells, metal-air batteries received significant interest in the last decade. The limited availability of traditional fossil fuel demands renewable energy resources. The electrochemical oxygen reduction and oxygen evolution reaction are the key processes in energy conversion and storage devices like metal-air batteries. The development of rechargeable metal-air batteries requires efficient bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Traditionally, Pt-, Ru- and Ir-based materials have been used for ORR and OER.1 The large overpotential due to the slow electron transfer kinetics, high cost and the electrochemical instability of these traditional precious metal-based electrocatalysts demands for active non-precious bifunctional catalysts. Moreover, the use of these traditional catalysts as an oxygen electrode is limited as they are not able to catalyse both the ORR and OER simultaneously. In the recent past, the oxides of transition metals such as Co, Mn, etc. including mixed valence spinel and perovskites have been proposed as alternate catalyst for these reactions.2 However, the poor electronic conductivity and the recyclability of these oxides limits their potential application.3 Recently, the hybrid electrocatalyst based on carbon and transition metal catalyst is emergingfor ORR and OER reactions.4 Our group is interested in the development of new functional materials for fuel cell and supercapacitor applications.2a,5 In continuation of our earlier efforts, herein we demonstrate the synthesis of two types of low-cost transition metal (Co, Fe) based hybrid bifunctional electrocatalyst. The two catalysts cobalt and nitrogen dual-doped carbon (Co-N-C) and reduced graphene oxide-CoFe (rGO-CoFe) were synthesized by chemical method followed by thermal annealing at an optimized temperature. The Co-N-C catalyst was obtained from cobalt tetra-aza macrocycle (Co-TET-A) whereas the rGO-CoFe catalyst was synthesized from multimetal complex, cobalt hexacyanoferrate. Both the catalysts were characterized by analytical techniques including XPS, TEM and XRD. The electrocatalytic response towards ORR and OER was evaluated by hydrodynamic voltammetry. The Co-N-C and rGO-CoFe catalysts show the limiting current density of -4.37 mA/cm2 and -5.58 mA/cm2, respectively and both the catalysts promote the 4-electron pathway for the reduction of oxygen. The OER activity was evaluated by measuring the overpotential at which 10 mA/cm2 current density was observed. Interestingly both Co-N-C and rGO-CoFe catalysts show the benchmark current density of 10 mA/cm2 at a low overpotential of 0.28 V and 0.22 V, respectively. The overall oxygen electrode activities were evaluated by calculating the difference in potential (ΔE) between the OER current density at 10 mA/cm2 and the ORR current density at −3 mA/cm2. We could achieve a ΔE of 0.92 V and 0.82 V on Co-N-C and rGO-CoFe catalyst respectively, confirming the efficient bifunctional activity of these catalysts. It is demonstrated that the synergistic effect between the metal and carbon and the porous nature of the catalysts plays an important role in the bifunctional activity. The detailed synthetic and bifunctional activity will be discussed.

Oxygen Reduction Reaction at Multi-Copper Complexes Investigated by Modified Electrode and In Situ XAFS

The oxygen reduction reaction (ORR), which occurs at the cathode in polymer electrolyte fuel cells (PEFCs), requires a large overpotential (more than 200 mV) even at the highly active platinum group metal (PGM) catalysts, since this reaction contains 4-electrons and 4-protons transfer to yield two water molecules from a dioxygen molecule. However, the biocathodes which are constructed by covalently attaching multi-copper enzymes, such as laccase (Lac), at electrode surfaces show nonexsistent overpotential (ca. 20 mV) toward ORR[1-2]. Unfortunately, the pH region, where the Lacs works well as an electrocatalyst for ORR, is limited and the spatial density of reactive sites at such the biocathode seems to be insufficient as compared with the state-of-the-art PGM electrocatalysts. Thus, the extraction of reactive sites in Lac and the effective arrangement on catalyst supports have been desired[3]. Recently, Gewirth and co-workers have achieved a preparation of binuclear copper complex, Cu2(Hdatrz)2, as an electrocatalyst for ORR[4-6]. Although the catalyst shows relatively large overpotential for ORR in acidic solution, the activity in alkaline solution is quite high. The active site for ORR in the catalyst has been proved to be bi-copper centers [6-7] and the investigation of ORR mechanism at the catalyst seems to be valuable.In the present study, we have adopted in situ X-ray absorption fine structure (XAFS) spectroscopy to monitor the electronic structure of Cu centers during ORR and to determine the molecular structure of Cu2(Hdatrz)2 complexes on electrodes. In situ XANES measurement has shown that the ORR at the Cu centers requires the formation of CuI species and the rate-determining step for ORR is dependent on pH.For further development of metal complex catalysts by replacing Cu centers to other metal ions, a easy preparation of model complex electrode should be required. Chemically modified model electrodes are also constructed on gold surface to investigate ORR at multi-metal complex using electrochemistry and spectroscopic methods. This work was supported by New Energy, Industrial Technology Development Organization (NEDO). XAFS experiments were performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2010G200 and 2013G173)[1] N. Mano, V. Soukharev, A. Heller, J. Phys. Chem. B, 110, 11180 (2006)[2] M.S. Thorum, C.A. Anderson, J.J. Hatch, A.S. Campbell, N.M. Marshall, S.C. Zimmerman, Y. Liu, A.A. Gewirth, J. Phys. Chem. Lett, 1, 2251 (2010)[3] C.H. Kjargaard, J. Rossmeisi, J.K. Norskov, Inorg. Chem., 49, 3567 (2010)[4] M.S. Thorum, J. Yadav, A.A. Gewirth, Ang. Chem. Int. Ed., 48, 165 (2008)[5] F.R. Brushett, M.S. Thorum, N.S. Lioutas, M.S. Naughton, C. Tornow, H-R. M. Jhong, A.A. Gewirth, P.A. Kenis, J. Am. Chem. Soc., 132, 12185 (2010)[6] M.S. Thorum, J.M. Hankett, A.A. Gewirth, J. Phys. Chem. Lett., 2, 295 (2011)[7] C.C.L. McCrory, A. Devadoss, X. Otterwaelder, R.D. Lowe, T.D.P. Stack, C.E.D. Chidsey, J. Am. Chem. Soc., 133, 3696 (2011)

ChemInform Abstract: Trends in the Chemistry of Mono‐ to Multimetal π‐Arene Complexes of Chromium and Manganese

AbstractReview: 105 refs.

Highly-Effective Structural Modulation of Trisaloph Heterotetranuclear Zn3La Complex by Anion Coordination

Abstract A trisaloph ligand L1, in which the three saloph units are macrocyclically incorporated, is a versatile multidentate ligand that maintains the multimetal complex. Structural modulation of the trisaloph complexes by anion coordination would offer more functions than the usual saloph metal complexes. In this study, the anion exchange of the heterotetranuclear complex 1(TfO)3 was applied to prepare various complexes. The two isomers, uuu- and uud-isomers, in which the coordination sites of the anions are different, were formed. The uuu-isomer was very selectively formed by using anions having a phosphate or C3-symmetric tricarboxylate.

Trends in the chemistry of mono- to multimetal π-arene complexes of chromium and manganese

The preparation and the features of the ring activation in π-arene metal (chromium, manganese) complexes are discussed. The bottom-up approach to the synthesis of σ, π-bi- and multimetal complexes, and the synthesis of cyclometallated and multicyclic complexes from a variety of selected routes are also reviewed. The stereochemical features of such complexes, and their applications in carbon–carbon coupling reactions and metal insertion reactions are highlighted. The redox reactivities and selected applications of (multi)metal π-arene complexes in catalysis and organic synthesis are included. Finally, the extension of the multimetal π-arene complexes to larger assemblies is shown. The importance of arene ring substituents in the basic mononuclear units and their use as bidentate metalloligands, with bidentate amines as linkers, in the construction of polymers, metal organic frameworks, networks (also on nanoparticles or silica supports), is highlighted.

ChemInform Abstract: Cooperative Formation and Functions of Multimetal Supramolecular Systems

AbstractReview: 72 refs.

Cooperative formation and functions of multimetal supramolecular systems

Multimetal complexes provide a variety of interesting structures, unique properties, and functions. Such sophisticated functions are often produced by synergistic and cooperative interactions among the metal ions accumulated in the restricted small area of the multimetal systems. We describe novel three strategies (i.e., macrocyclic, C-shape, and multimetal template) for the preparation of the multimetal supramolecular systems by the cooperative metal binding of a multi-Schiff-base and multi-oxime ligands, and their characteristic structures and functions. The three approaches are versatile and effective because the employed coordination reactions smoothly and quickly proceeded under mild conditions to quantitatively form the desired coordination structures. The multimetal supramolecular systems obtained here exhibit the synergistic and cooperative functions for ion recognition, magnetic properties, helicity control, and modulation of reaction selectivity. These types of multimetal complexes could be developed for a cascade functional supramolecular system that shows highly synergistic properties, integrated multifunctions, and function amplification.

Programmed multiple complexation for the creation of helical structures from acyclic phenol–bipyridine oligomer ligands

Two new multidentate ligands, H3L(1) and H4L(2), possessing bipyridine-phenol repetitive units were designed so that the multi-metal complexation could produce a single-helical structure in a pre-programmed fashion. The ligands were synthesized by successive palladium-catalyzed coupling reactions. The complexation of H3L(1) with zinc(II) and nickel(II) acetate afforded [L(1)Zn2(OAc)] and [(L(1))2Ni4](OAc)2, respectively. Each of the ligand moieties in these complexes formed a one-turn single helix. The zinc(II) complex [L(1)Zn2(OAc)] underwent a helix compression-extension motion in solution. The complexation of the H3L(1) ligand with iron(III) chloride gave a dinuclear complex [(HL(1))2Fe2Cl2] with a non-helical dimeric structure. The longer ligand H4L(2) afforded a trinuclear complex [L(2)Zn3(OAc)2] with a 1.5-turn single-helical structure upon complexation with zinc(II) acetate. The reaction of the H4L(2) ligand with cobalt(II) acetate under aerobic conditions gave a mixed valence complex [L(2)Co3(OAc)3(OMe)], which had two trivalent and one divalent cobalt ions. The structural features of the trinuclear complexes significantly depended on the metals; [L(2)Co3(OAc)3(OMe)] had a helical pitch of 7.6 Å, which was almost twice that of [L(2)Zn3(OAc)2] (4.0 Å).