Coordination Chemistry Approach Research Articles

Redox- and Charge-State Dependent Trends in 5, 6, and 7-Membered Boron Heterocycles: A Neutral Ligand Coordination Chemistry Approach to Boracyclic Cations, Anions, and Radicals.

ConspectusBoron heterocycles represent an important subset of heteroatom-incorporated rings, attracting attention from organic, inorganic, and materials chemists. The empty pz orbital at the boron center makes them stand out as quintessential Lewis acidic molecules, also serving as a means to modulate electronic structure and photophysical properties in a facile manner. As boracycles are ripe for extensive functionalization, they are used in catalysis, chemical biology, materials science, and continue to be explored as chemical synthons for conjugated materials and reagents. Neutral boron(III)-incorporated polycyclic molecules are some of the most studied types of boracycles, and understanding their redox transformations is important for applications relying on electron transfer and charge transport. While relevant redox species can often be electrochemically observed, it remains challenging to isolate and characterize boracycles where the boron center and/or polycyclic skeleton have been chemically reduced.We describe our recent work isolating 5-, 6-, and 7-membered boracyclic radicals, anions, and cations, focusing on stabilization strategies, ligand-mediated bonding situations, and reactivity. We present a versatile neutral ligand coordination chemistry approach that permits the transformation of boracycles from potent electrophiles to powerful nucleophilic heterocycles that facilitate diverse electron transfer and bond activation chemistry. Although there are a wide range of suitable stabilizing ligands, we have employed both diamino-N-heterocyclic carbenes (NHCs) and cyclic(alkyl)(amino) carbenes (CAACs), which led to boracycles with tunable electronic structures and aromaticity trends. We highlight successful isolation of borafluorene radicals and demonstrate their reversible redox behavior, undergoing oxidation to the cation or reduction to the anion. The borafluorene anion is a chemical synthon that has been used to prepare boryl main-group and transition-metal bonds, luminescent oxabora-spirocycles, borafluorenate-crown ethers, and CO-releasing molecules via carbon dioxide activation. We expanded to 6-membered boracycles and characterized neutral bis(NHC-supported 9-boraphenanthrene)s and the corresponding bis(CAAC-stabilized 9-boraphenanthrene) biradical. We detail the interconvertible multiredox states of boraphenalene, where the boraphenalenyl radical, anion, and cation mimic the charge-states of the all-hydrocarbon analogue. Reactivity studies of the boraphenalenyl anion displayed unusual nucleophilic reactivity at multiple sites on the periphery of the boraphenalenyl tricyclic scaffold. Reduced borepins, 7-membered boron containing heterocycles, have also been isolated. We used a stepwise one-pot synthesis combining the halo-borepin precursor, CAAC, and KC8 to afford the monomeric borepin radicals and anions. The π-system was extended to contain two borepin rings fused in a pentacyclic scaffold, which permitted isolation of diborepin biradicals and a diborepin containing a dibora-quinone core.Our goal is to provide a guide explaining the current structure-function trends and isolation strategies for redox-active boron-incorporated polycyclic molecules to initiate the rational design and use of these types of compounds across a vast chemical space.

Recycling primary lithium batteries using a coordination chemistry approach: recovery of lithium and manganese residues in the form of industrially important materials.

In this study, we have investigated the potential use of post-consumer primary lithium metal batteries (LMBs) commonly used in portable electronic devices to recover lithium and manganese in the form of industrially important materials. A direct reaction of lithium-containing electronic waste with a naturally sourced ester, methyl salicylate, combined with a wide range of aliphatic alcohols has been used as a general method for recovering lithium in the form of lithium aryloxides of different nuclearities [Li(OAr)(HOMe)2] (1), [Li(OAr)(HOAr)] (2), [Li(OAr)(HOEt)]2 (3), [Li(OAr)(H2O)]2 (4), [Li4(OAr)4(EGME)2] (5), [Li6(OAr)6] (6-8) for ArOH = methyl salicylate (1, 2, 4, 6), ethyl salicylate (3, 7), 2-methoxyethyl salicylate (5, 8), and EGME = 2-methoxyethanol. The hydrolysis of 7 was then used to synthesize lithium salicylate [Li(Sal)(H2O)]n (10), which is an important antioxidant in the production of oils and grease. The discharged cathode material of Li-MnO2 batteries was investigated as a source from which LiClO4, Li2CO3, LiMn2O4, and Mn2O3 can be recovered by means of water-alcohol extraction or calcination. Particular emphasis was placed on the detailed characterization of all battery components and their decomposition products. LMBs were completely recycled for the first time, and materials were recovered from the cathode and the anode.

Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization.

The most efficient and stable perovskite solar cells (PSCs) are made from complex mixture of precursors, which are practically always dissolved in combinations of the volatile (and toxic) N, N-Dimethylformamide (DMF), and the non-volatile (and green) dimethyl sulfoxide (DMSO) solvents. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g. by vacuum, an airstream or a so-called antisolvent. Unfortunately, most such oversaturation triggers do not expel the lingering (and highly coordinating) DMSO, which is highly coordinating, from the thin films; this detrimentally affects long-term stability. Here, for the first time, we introduce (the green) dimethyl sulfide (DMS) as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. More precisely, DMS coordinates more strongly than all currently used solvents, hence replacing them, including DMSO, effectively during film formation. Crucially, DMS also has among the highest vapor pressures reported in literature, thus effectively leaving the thin film shortly after formation. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, we process MAPbI3 PSCs, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of our strategy, we tested DMS for FAPbI3 as another composition, which showed higher efficiency of 23.5% compared to 20.9% for fabricated device with CB. This work provides a universal strategy to control perovskite crystallization using coordination chemistry heralding the revival of perovskite compositions with pure DMSO, such as MAPbI3 . This article is protected by copyright. All rights reserved.

Synthesis and metalation of polycatechol nanohoops derived from fluorocycloparaphenylenes.

Due to their unique topology and distinct physical properties, cycloparaphenylenes (CPPs) are attractive building blocks for new materials synthesis. While both noncovalent interactions and irreversible covalent bonds have been used to link CPP monomers into extended materials, a coordination chemistry approach remains less explored. Here we show that nucleophilic aromatic substitution reactions can be leveraged to rapidly introduce donor groups (-OR, -SR) onto polyfluorinated CPP rings. Demethylation of methoxide-substituted CPPs produces polycatechol nanohoop ligands that are readily metalated to produce well-defined, multimetallic CPP complexes. As catechols are recurring motifs throughout coordination chemistry and dynamic covalent chemistry, the polycatechol nanohoops reported here open the door to new strategies for the bottom-up synthesis of atomically precise CPP-based materials.

Identification of metal binding motifs in protein frameworks to develop novel remediation strategies for Hg2+ and Cr(VI).

Amino acid sequences in metal-binding proteins with chelating properties offer exciting applications in biotechnology and medical research. To enhance their application in bioremediation studies, we explicitly aimed to identify specific metal-binding chelating motifs in protein structures for two significant pollutants, such as mercury (Hg2+) and chromium Cr(V1). For this purpose, we have performed an extensive coordination chemistry approach by retrieving Hg2+ and Cr(V1) binding protein structures from the protein database and validated using the B-factor, a term defining uncertainty of the atoms and with occupancy to obtain the best binding motifs. Our analysis revealed that acidic amino acids like aspartic acid, glutamic acid, and basic amino acids such as cysteine and histidine are predominant in coordinating with these metals. The order of preference in Hg2+-bound structures is predicted to be Cys > His > Asp > Glu, and for Cr(V1) is His > Asp > Glu. Examination of the atomic coordinates and their distance from each metal revealed that the sulfur atoms of cysteine showing more preference towards Hg2+coordination with an atomic distance ranging from 1.5 to 2.9Å. Likewise, oxygen atoms of aspartic acid, glutamic acid and nitrogen atoms of histidine are within 2Å of Cr(V1) coordination. Based on these observations, we obtained C-C-C, C-X(2)-C-C-(X)2-C, H-C-H motifs for Hg2+, and D-X(1)-D, H-X(3)-E motif for Cr(V1) to be shared within the coordination space of 3Å. As a future scope, we propose that the identified metal-binding chelating motifs are oligopeptides and can display on the surface of microorganisms such as Escherichia coli and Saccharomyces cerevisiae for effective removal of natural Hg2+ and Cr(V1) through biosorption. Hence, our results will provide the basis for futuristic bioremediation.

Surface modified zinc ferrite as a carbon-alternative negative electrode for high-energy hybrid supercapacitor

The limited energy storage capacities of carbon-based negative electrodes, which rely on conventional double layer charge storage mechanisms, have limited the electrochemical performances of hybrid supercapacitors (HSCs). The development of nanostructured redox-active materials that serve as alternatives to carbon-based negative electrodes is crucial to overcome the limitations of current HSCs. In this work, a coordination chemistry approach is utilized to tune the nanostructure of zinc ferrite thin films on flexible stainless steel (SS) foil by using several zinc salt precursors, including ZnCl2·6H2O, Zn(NO3)2·6H2O, and ZnSO4·6H2O, while using the same iron precursor (FeCl2·4H2O). Materials prepared with the ZnCl2·6H2O metal salt form porous nanosheets with groundnut-like structures that exhibit maximum specific capacities of 544 mA h/g (454 F/g) at current density of 2.5 A/g. Redox-active solid-state HSCs are assembled by using zinc ferrite as a negative electrode, MnO2 nanoflakes as a positive electrode, and a polymer gel as the electrolyte. The developed solid-state HSC cells show excellent performance as exemplified by a maximum specific capacitance of 123.8 F/g and an energy density of 55.72 Wh/kg, both of which are superior to those of conventional carbon-based symmetric and HSCs.

Tea from the drinking to the synthesis of metal complexes and fabrication of PVA based polymer composites with controlled optical band gap

In the present study black tea extract (BTE) solution which is familiar for drinking was used to prepare cerium metal-complexes (Ce(III)-complex). The prepared Ce(III)-complex was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV–Vis spectroscopy. The results indicate that BTE solution is a novel green coordination chemistry approach for the synthesis of metal complexes. The outcomes signify that coordination occurs between cerium cations and polyphenols. The synthesis of metal-complexes with superior absorption performance in the visible region is a challenge for optoelectronic device applications. The suspended Ce(III)-complex in distilled water was mixed with poly (vinyl alcohol) (PVA) polymer to fabricate PVA/ Ce(III)-complex composites with controlled optical properties. The PVA/Ce(III)-complexes composite films were characterized by FTIR, XRD, and UV–Vis spectroscopy. The XRD findings confirms the amorphous structure for the synthesized Ce(III)-complexes. The addition of Ce(III)-complex into the PVA host polymer led to the growth of polymer composites with controllable small optical band gaps. It is shown by the FTIR spectra of the composite films that the functional groups of the host PVA have a vigorous interaction with the Ce(III)-complex. The XRD deconvolution on PVA composites reveals the amorphous phase enlargement with increasing Ce(III)-complex concentration. It is indicated in the atomic force microscopy (AFM) that the surface roughness in the doped PVA films increases with the increase of the Ce(III)-complex. There is a decrease in absorption edge from 5.7 to 1.7 eV. It becomes possible to recognize the type of electron transition by studying both the Tauc's model and optical dielectric loss (ɛi) parameter.

Combined Experimental and Theoretical Molecular Approach of the Catalytically Active Hydrotreating MoS2 Phases Promoted by 3d Transition Metals

High-throughput synthesis combined with a surface organometallic (coordination) chemistry approach is used to prepare in a systematic way a series of 40 metal-promoted (Me)–MoS2 active phases suppo...

Model for Metal Extraction from Chloride Media with Basic Extractants: A Coordination Chemistry Approach

The metal extraction mechanism of basic extractants is typically described as an anion exchange process, but this mechanism does not correctly explain all observations. This paper introduces a novel model for the extraction of metals by basic extractants from chloride media supported by experimental data on methyltrioctylammonium chloride and Aliquat 336 chloride systems. This model relies on the hypothesis that the metal species least stabilized in the aqueous phase by hydration (i.e., the metal species with the lowest charge density) is extracted more efficiently than the more water stabilized species (i.e., species with higher charge densities). Once it is transferred to the organic phase, the extracted species can undergo further Lewis acid-base adduct formation reactions with the chloride anions available in the organic phase to form negatively charged chloro complexes, which than associate with the organic cations. Salting-out agents influence the extraction, most likely by decreasing the concentration of free water molecules, which destabilizes the metal complex in the aqueous phase. The evidence provided includes (1) the link between extraction and transition-metal speciation, (2) the trend in extraction efficiency as a function of the concentration of different salting-out agents, and (3) the behavior of HCl in the extraction system. The proposed extraction model better explains the experimental observations in comparison to the anion exchange model and allows the prediction of optimal conditions for metal extractions and separations a priori, by selecting the most suitable salting-out agent and its concentration.

Modeling the Solvent Extraction of Cadmium(II) from Aqueous Chloride Solutions by 2-pyridyl Ketoximes: A Coordination Chemistry Approach.

The goal of this work is to model the nature of the chemical species [CdCl2(extractant)2] that are formed during the solvent (or liquid-liquid) extraction of the toxic cadmium(II) from chloride-containing aqueous media using hydrophobic 2-pyridyl ketoximes as extractants. Our coordination chemistry approach involves the study of the reactions between cadmium(II) chloride dihydrate and phenyl 2-pyridyl ketoxime (phpaoH) in water-containing acetone. The reactions have provided access to complexes [CdCl2(phpaoH)2]∙H2O (1∙H2O) and {[CdCl2(phpaoH)]}n (2); the solid-state structures of which have been determined by single-crystal X-ray crystallography. In both complexes, phpaoH behaves as an N,N’-bidentate chelating ligand. The complexes have been characterized by solid-state IR and Raman spectra, and by solution 1H NMR spectra. The preparation and characterization of 1∙H2O provide strong evidence for the existence of the species [CdCl2(extractant)2] that have been proposed to be formed during the liquid-liquid extraction process of Cd(II), allowing the efficient transfer of the toxic metal ion from the aqueous phase into the organic phase.

PGM-Free ORR Catalysts Designed by Templating PANI-Type Polymers Containing Functional Groups with High Affinity to Iron

In this work, a coordination-chemistry approach was used to increase the content of nitrogen-coordinated iron moieties (Fe-Nx) in platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR). The catalysts were derived from a series of polyaniline (PANI)-type precursors with N-containing functional side chains having high affinity to iron. The PGM-free ORR catalysts synthesized using such polymeric templates were characterized by scanning electron microscopy, X-ray diffractometry, and tested in an electrochemical cell and H2-air fuel cell for ORR activity. X-ray photoelectron spectroscopy (XPS) analysis showed that, in spite of similar nitrogen contents, catalysts obtained using PANI-type polymers containing side chains with high affinity to iron had higher Fe content than PANI-derived catalyst. These PGM-free catalysts showed improved ORR activity in an electrochemical cell and in H2-air fuel cell testing, compared to the PANI-derived catalyst. A correlation between the content of Fe-Nx moieties and the fuel cell performance was observed in these PGM-free ORR catalysts.

A Coordination Chemistry Approach for Lithium-Ion Batteries: The Coexistence of Metal and Ligand Redox Activities in a One-Dimensional Metal-Organic Material.

We demonstrate herein the use of a one-dimensional metal-organic material as a new type of electrode material for lithium-ion batteries (LIBs) in place of the classic porous three-dimensional materials, which are subject to the size of the channel for lithium-ion diffusion and blocking of the windows of the framework by organic solvents during the charging and discharging processes. Introducing a one-dimensional coordination compound can keep organic active substances insoluble in the electrolyte during the charging and discharging processes, providing a facile and general new system for further studies. The results show that both the aromatic ligand and the metal center can participate in lithium storage simultaneously, illustrating a new energy storage mechanism that has been well-characterized by X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. In addition, the fact that the one-dimensional chains are linked by weak hydrogen bonds rather than strong π-π stacking interactions or covalent bonds is beneficial for the release of capacity entirely without the negative effect of burying the active sites.

Synthesis, characterization, and evaluation of the antimicrobial potential of copper(II) coordination complexes with quinolone and p-xylenyl-linked quinolone ligands

The antimicrobial properties of copper have been known to mankind since the ancient times. In a coordination chemistry approach to develop novel antimicrobial agents, the quinolone antimicrobial agents ciprofloxacin (Hcipro) and pipemidic acid (Hpia), as well as dimers thereof (piperazinyl-linked with a p-xylenyl moiety) were complexed with copper(II). The synthesis and antimicrobial evaluation of bis(ciprofloxacino)copper(II) [Cu(cipro)2], bis(pipemido)copper(II) [Cu(pia)2], and the corresponding dimer complexes, [Cu2(ciproXcipro)2] and [Cu2(piaXpia)2], are reported. No combinational or synergistic effect between copper(II) and the respective quinolone ligands was observed in vitro.

A coordination chemistry approach for shape controlled synthesis of indium oxide nanostructures and their photoelectrochemical properties

False color scanning electron microscopic images of indium hydroxide cubes, maize corns and indium sulfate hydroxide hydrate crystals.

The First Hexadithienylethene‐Substituted Tris(bipyridine)metal Complexes as Quadratic NLO Photoswitches: Combined Experimental and DFT Studies

Flip the NLO switch! A straightforward access to hexadithienylethene-based photochromes by using a coordination-chemistry approach through the combination of bis(dithienylethene)bipyridyl ligands and metal ions (M = Zn, Fe) is reported. The photostability of the isomeric forms of the iron(II) complexes allows the photoswitching of second-order nonlinear optical (NLO) responses (see figure), and the results are rationalized with the help of time-dependent density functional theory.

From Simple Chalcogenidotetrelate Precursors to Complex Structures and Functional Compounds

AbstractChalcogenidotetrelates show a rich and complex chemistry encompassing intricate structures and useful materials. A step‐wise coordination chemistry approach allows the sequential formation of multinary M/T/E anions (M = transition metal, T = tetrel, E = chalcogen) from simple T/E building blocks in solution. This way, a range of compounds displaying different structure types of molecular as well as extended multinary anions were obtained. To allow for even further variety, the approach can be extended to organo‐functionalized chalcogenidotetrelates. Here, the organic shell of the inorganic cages plays a decisive role in reactivity and resulting structures. The formation structures and properties of these compounds will be discussed in detail in this perspective article.

Photoelectrochemistry of solution processed hematite nanoparticles, nanoparticle-chains and nanorods

We report a coordination chemistry approach for shape-controlled synthesis of α-Fe2O3 (hematite) nanostructures. Three distinct morphologies viz. nanoparticles, nanoparticle-chains and nanorods were synthesized from inorganic iron precursor sources of nitrate, sulfate and chloride, respectively, in the presence of urea as a pH regulating agent and were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The responsible growth mechanism and possible factors controlling the morphologies are explored. Photoelectrochemical cells constructed by utilizing these nanostructures produced stable photocurrents in iodide electrolyte. The nanoparticle-chains morphology of α-Fe2O3 revealed the highest photocurrent density of 0.36 mA cm−2 at 0 V bias conditions under 1 Sun illumination. The reason for the high performance is investigated with the help of impedance spectroscopy analysis, wherein the electrode composed of nanoparticle-chains affords the lowest charge transfer resistance and thereby the highest photoconversion yield, as compared to those of the nanoparticle and nanorod electrodes.

Electroactive copper(II) bimetallic self-assembled multilayers on Si(100)

Silicon (100) surfaces were modified by reacting 4-aminopyridine and Si–Cl bond. These surfaces were further used for tethering copper bimetallic complexes and growing monolayers and multilayers by changing the axial position via Lewis acid–base reactions. In this way, coordination chemistry approach can be used as building blocks for controlling the design of functional surfaces. Furthermore, the outcomes of the several characterization techniques indicate that the complex is spatially oriented suggesting that this simple strategy allows the preparation of three dimensional molecular structures exhibiting spatial order. The structures on surface show interesting electroactive behaviors leading two cathodic signals, that can be related to Cu(II)/Cu(I) and Cu(I)/Cu(0) electro-reduction species (signals at −0.15V and −0.50V) and one peak in the anodic region (−0.15V) ascribed to the Cu(0)/Cu(II) electro-oxidation reaction, using an Ag/AgCl saturated electrode and platinum wire as reference and counter electrodes, respectively.

Coordination chemistry approach for the end-to-end assembly of gold nanorods

Gold nanorods synthesized by radiolysis were selectively end-functionalized by a fully conjugated thiol bearing a pendant terpyridine group; addition of ferrous ions led to the end-to-end 1D self-assembly of the nanorods. Similar results have been obtained when the preformed [(HStpy)Fe(tpySH)] 2+ dithiol complex was directly added to the gold nanorods.

Coordination chemistry approach to the long-standing challenge of stereocontrolled chemical glycosylation

This study clearly demonstrates that a multi-dentate metal coordination to the leaving group, along with O-5 and/or a protecting group at O-6, has a strong effect on the stereoselectivity of chemical glycosylation.