Bidentate Research Articles

57Fe nuclear resonance vibrational spectroscopic studies of tetranuclear iron clusters bearing terminal iron(iii)-oxido/hydroxido moieties.

57Fe nuclear resonance vibrational spectroscopy (NRVS) has been applied to study a series of tetranuclear iron ([Fe4]) clusters based on a multidentate ligand platform (L3-) anchored by a 1,3,5-triarylbenzene linker and pyrazolate or (tertbutylamino)pyrazolate ligand (PzNH t Bu-). These clusters bear a terminal Fe(iii)-O/OH moiety at the apical position and three additional iron centers forming the basal positions. The three basal irons are connected with the apical iron center via a μ4-oxido ligand. Detailed vibrational analysis via density functional theory calculations revealed that strong NRVS spectral features below 400 cm-1 can be used as an oxidation state marker for the overall [Fe4] cluster core. The terminal Fe(iii)-O/OH stretching frequencies, which were observed in the range of 500-700 cm-1, can be strongly modulated (energy shifts of 20-40 cm-1 were observed) upon redox events at the three remote basal iron centers of the [Fe4] cluster without the change of the terminal Fe(iii) oxidation state and its coordination environment. Therefore, the current study provides a quantitative vibrational analysis of how the remote iron centers within the same iron cluster exert exquisite control of the chemical reactivities and thermodynamic properties of the specific iron site that is responsible for small molecule activation.

Studies on the behavior of the bis-complex of Pt(IV) with the tridentate ligand all-cis-2,4,6-triaminocyclohexane-1,3,5-triol in aqueous solutions

NMR spectroscopy and high-resolution mass spectrometry were applied to study the stability of the complex cation [Pt(taci)2]4+ known as ditaciplatin in aqueous solutions at varying acidity and in the presence of monodentate ligands. Ditaciplatin is a cationic part of the bis-complex of Pt(IV) with the tridentate ligand all-cis-2,4,6-triaminocyclohexane-1,3,5-triol (taci) with a composition [Pt(taci)2](CO3)2·6H2O (2A). It was found that the ditaciplatin complex is stable in solution at all of the studied conditions within the period of 7 days. Three new compounds were isolated in the experiments in solution, namely: [Pt(taci)2](CO3)1.5(OH)·7H2O (2B), [Pt(taci)2](Cl)4·H2O (2C) and [Pt(taci)2](NO3)4·2H2O (2D). 2B and 2C crystalize in triclinic crystal system P-1 and 2D – in monoclinic Р21/n. The cationic part of the compounds is ditaciplatin and the counterions depend on the synthetic conditions.

Synthesis, characterization, and anticancer activity of Co(II), Cu(II), and Zn(II) complexes containing mefenamic acid and 2-methylimidazole

Mefenamic acid (mef), a widely used nonsteroidal anti-inflammatory drug in pain treatment, was utilized as the starting material in synthesizing three metal (II) complexes in the presence of 2-methylimidazole (mei) co-ligand. The newly synthesized complexes, [Co(mef)2(mei)2(C2H5OH)2]; (1), [Cu(mef)2(mei)2(C2H5OH)2]; (2), and [Zn(mef)2(mei)2]; (3), were characterized using elemental analysis, spectroscopic techniques (FTIR, UV–Vis), thermal analysis, and single crystal X-ray crystallography. Complex (3) was further characterized by 1H and 13C NMR and PXRD. FTIR studies confirmed the coordination of mefenamato ligand and 2-methylimidazole in the complexes, while TG analysis determined their compositions and thermal stability. Complexes (1) and (2) were found to be isostructural, with an octahedral geometry and surrounded by monodentate ligands, while complex (3) is a tetrahedral Zn(II) complex. In addition, the MTT test was used to investigate the cytotoxicity of mefenamic acid and the complexes on lung cancer cells (NCIH-460), breast cells (MDAMB), and normal cells (L929). Complex (1) demonstrated the most significant anti-MDAMB cell line activity.

Capacitive deionization of uranium mediated by dioxygen functionalities in the C = O = C = O segment of polyacrylic acid-functionalized graphene aerogel

The extraction of uranium is crucial for sustaining a consistent nuclear fuel cycle, yet the task of isolating uranyl ions from aqueous solutions presents formidable challenges. Herein, a PAA/GO aerogel was developed using polyacrylic acid-functionalized graphene, wherein the C = O = C = O segment's dual oxygen served both as electrodes for capacitive deionization and as sites for charge transfer and uranyl capture, effectively purifying uranium mine wastewater. Furthermore, under the stringent experimental conditions set at 298 K and a pH of 5.5, the PAA/GO composite demonstrated an impressive adsorption capacity of 898.7 mg g−1. When this composite was further amalgamated into the CDI architecture, it exhibited an impressive 92 % uranium extraction from genuine mine effluent at an unwavering potential of 0.9 V. Through density functional theory (DFT) analyses, the adsorption energies of [UO2(H2O)5]2+ with the PAA/GO composite involving C = O = C = O ligands displayed the highest value compared with PAA and PAA/GO composite (involving monodentate and bidentate ligands). The Bader charge analysis further indicating the greatest charge loss in the uranium ion. In conclusion, the novel PAA/GO aerogel 3D framework with its specific C = O = C = O regional chain sets a pioneering standard in uranium extraction techniques, showcasing unprecedented efficiency in UO22+ removal from aqueous solutions.

Antisolvent-Free Heterogenous Nucleation Enabled by Employing 4-Tert-Butyl Pyridine Additive and Two-Step Annealing for Efficient CsPbI2Br Perovskite Solar Cells.

All inorganic perovskite based on CsPbI2Br has attracted significant attention due to its relatively thermal stable structure compare to its hybrid counterparts. With a wide bandgap of 1.9eV and excellent light absorption capability, it has been extensively explored for applications in indoor photovoltaics and as a front absorber in tandem devices. However, the uncontrollable crystallization process during solvent evaporation and thermal annealing leads to both macroscopic defects like cracks and microscopic defects such as voids. In this study, a metastable adduct with lead (II) halides by incorporating 4-tert-butyl pyridine as a volatile Lewis base monodentate ligand in the precursor solution is formed. The strategic preferential decomposition of the adduct during the early-stage low-temperature annealing facilitated the desorption of lead (II) halides, inducing antisolvent-free heterogenous nucleation. This, in turn, promoted crystal growth during subsequent high-temperature annealing, resulting in dense films with low defect density. As a result, a maximum open-circuit voltage of 1.30V is achieved with the champion power conversion efficiency of 16.5% in CsPbI2Br-based perovskite solar cell. The work reveals a new mechanism of using Lewis acid-base adduct to obtain high quality perovskite films other than hindering crystallization in traditional way.

Tungsten Nitride/Tungsten Oxide Nanosheets for Enhanced Oxynitride Intermediate Adsorption and Hydrogenation in Nitrate Electroreduction to Ammonia.

Electrochemical NO3- reduction reaction (NO3RR) is a promising technique for green NH3 synthesis. Tungsten oxide (WO3) has been regarded as an effective electrocatalyst for electrochemical NH3 synthesis. However, the weak adsorption and the sluggish hydrogenation of oxynitride intermediates (NOx, e.g., *NO3 and *NO2) over WO3 materials hinder the efficiency of converting NO3- to NH3. Herein, we design a heterostructure of tungsten nitride (WN) and WO3 (WN/WO3) nanosheets to optimize *NO3 and *NO2 adsorptions and facilitate *NO2 hydrogenations to achieve a highly efficient electrochemical NO3RR to produce NH3. Theoretical calculations predict that locally introducing WN into WO3 will shorten the distance between adjacent W atoms, resulting in *NO3 and *NO2 being strongly adsorbed on W active sites in the form of bidentate ligands instead of the relatively weak monodentate ligands. Furthermore, WN facilitates H2O dissociation to supply the requisite protons, which is beneficial for *NO2 hydrogenations. Inspired by theoretical prediction, WN/WO3 nanosheets are successfully fabricated through a high-temperature nitridation process. The transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy investigations confirm that the amorphous WN has been locally introduced in situ into WO3 nanosheets to form a composite heterostructure. The as-prepared WN/WO3 nanosheets exhibit a high Faraday efficiency of 88.9 ± 7.2% and an appreciable yield rate of 8.4 mg h-1 cm-2 toward NH3 production, which is much higher than that of individual WO3 and WN. The enhanced adsorption and hydrogenation behaviors of *NOx over WN/WO3 are characterized by in situ Fourier-transform infrared spectroscopy, consistent with the theoretical predictions. This work develops facile and effective heterostructure nanomaterials to tune the adsorption and hydrogenation of NOx for boosting the efficiency from NO3- to NH3.

Defect mitigation using multi-dentate ligand in FASnI3 perovskite films

Tin-based perovskite shows a more rational band gap, along with lower exciton-binding energy, and is noted to be suitable for solar cell fabrication. One of the open questions is their lower environmental stability due to poor crystallinity and surface inhomogeneity. We probed the impact of sulfur-containing multi-functional additives in FASnI3 thin films, which interacts intensely with the Sn-based perovskites, and in turn, regulate the crystallization process to allow the preferential crystal growth along (h00) planes at the microscale. The single sulfur-containing ammonium cation (Isothio-Br) based perovskites showed improved crystallinity and microstructure as compared to the double sulfur-containing Disulfo-Cl molecule.

Synthesis, crystal structure and Hirshfeld surface analysis of a cadmium complex of naphthalene-1,5-di-sulfonate and o-phenyl-enedi-amine.

A novel o-phenyl-enedi-amine (opda)-based cadmium complex, bis-(benzene-1,2-di-amine-κ2 N,N')bis-(benzene-1,2-di-amine-κN)cadmium(II) naphthalene-1,5-di-sulfonate, [Cd(C6H8N2)4](C10H6O6S2), was synthesized. The complex salt crystallizes in the monoclinic space group C2/c. The Cd atom occupies a special position and coordinates six nitro-gen atoms from four o-phenyl-enedi-amine mol-ecules, two as chelating ligands and two as monodentate ligands. The amino H atoms of opda inter-act with two O atoms of the naphthalene-1,5-di-sulfonate anions. The anions act as bridges between [Cd(opda)4]2+ cations, forming a two-dimensional network in the [010] and [001] directions. The Hirshfeld surface analysis shows that the primary factors contributing to the supramolecular inter-actions are short contacts, particularly van der Waals forces of the type H⋯H, O⋯H and C⋯H.

Advancement in the synthesis of metal complexes with special emphasis on Schiff base ligands and their important biological aspects

Schiff bases and their metal complexes are versatile compounds synthesized from the condensation of an amino compound with carbonyl compound and widely used for the industrial purposes. They also exhibit a broad range of biological activities including antifungal, antimalarial, antiproliferative, antibacterial, antipyretic and antiviral. Many Schiff base complexes exhibit excellent catalytic activity in various reactions. The activity is usually increased by complexation therefore, to understand the properties of both ligands and metal can lead to the synthesis of highly active compounds. The influence of certain metals on the biological activity of these compounds and their intrinsic chemical interest as multidentate ligands has prompted a considerable increase in the study of their coordination behaviour. Development of new Schiff base metal complexes is now attracting the attention of medicinal chemists. This review compiles the synthesis of various multidentate Schiff bases ligands and their complexation with various metals such as Zr, V, Mo, Mn, Fe, Zn, Re, Cd, and Ln. This review is an attempt to congregate complete survey on synthesis and biological activity of Schiff base metal complexes that will give glimpse on the future directions for successful development and discovery of useful drugs.

ReaLigands: A Ligand Library Cultivated from Experiment and Intended for Molecular Computational Catalyst Design.

Computational catalyst design requires identification of a metal and ligand that together result in the desired reaction reactivity and/or selectivity. A major impediment to translating computational designs to experiments is evaluating ligands that are likely to be synthesized. Here, we provide a solution to this impediment with our ReaLigands library that contains >30,000 monodentate, bidentate (didentate), tridentate, and larger ligands cultivated by dismantling experimentally reported crystal structures. Individual ligands from mononuclear crystal structures were identified using a modified depth-first search algorithm and charge was assigned using a machine learning model based on quantum-chemical calculated features. In the library, ligands are sorted based on direct ligand-to-metal atomic connections and on denticity. Representative principal component analysis (PCA) and uniform manifold approximation and projection (UMAP) analyses were used to analyze several tridentate ligand categories, which revealed both the diversity of ligands and connections between ligand categories. We also demonstrated the utility of this library by implementing it with our building and optimization tools, which resulted in the very rapid generation of barriers for 750 bidentate ligands for Rh-hydride ethylene migratory insertion.

Photoinduced Carbon−Heteroatom Cross‐Coupling Catalyzed by Nickel Naphthyridine Complexes

AbstractWe describe versatile and practical light‐promoted C−N and C−O cross‐coupling reactions catalyzed by NiII complexes supported by 2,7‐dimethyl‐1,8‐naphthyridine ligand. Using the same Ni catalyst and visible light irradiation, both C−O and C−N coupling reactivity was observed without additional photocatalysts. These results demonstrate that Ni naphthyridine complexes represent a versatile catalytic motif for photoredox nickel catalysis alternative to commonly used bipyridines or multidentate ligands.

Cascading Energy Transfer for Highly Efficient Deep-Red OLED Emission with Cyclometalated [3+2+1] Iridium Complexes.

The promising cyclometalated iridium (III) complexes have been proved to possess great potential in vacuum-deposited organic light-emitting diodes (OLEDs) applications for full-color displays and white solid-state lighting sources. Herein, based on the unique bidentate ligand of dibenzo[a,c]phenazine (dbpz) group with strong conjugated effect of aromatic rings for red emission, four novel [3+2+1] coordinated iridium (III) emissive materials have been rationally designed and synthesized. The monodentate ligands of -CN and -OCN have been effectively employed to tune the deep-red emission of 628-675nm with high photoluminescence quantum yields up to 98%. Moreover, all devices displayed deep-red color coordinates ranging from (0.675, 0.325) to (0.716, 0.284), which is close to the standard-red color coordinates of (0.708, 0.292), as recommended by International Telecommunication Union Radiocommunication (ITU-R) BT.2020. The device based on nBuIr(dbpz)CN with an exciplex cohost has exhibited maximum external quantum efficiencies of 20.7% and good stability. With nBuIr(dbpz)CN as an effective sensitizer, the nBuIr(dbpz)OCN based phosphorescent OLED devices have successfully demonstrated cascading energy transfer processes, contributing to pure red emission with maximum luminance as high as 6471cd m-2. Therefore, this work has been successfully demonstrated rational molecular design strategy of [3+2+1] iridium complexes to obtain highly efficient deep-red electrophosphorescent emission.

Highly selective recovery of yttrium from mining wastewater using biosynthetic iron sulfide nanoparticles

The selective recovery of rare earth elements (REEs) from mining wastewater has become a hot research topic due to the increasing industrial value of REEs. Herein, biosynthetic iron sulfide nanoparticles (nFeS) were deployed as a superior adsorbent to selectively recover Y(Ⅲ) from mining wastewater. The maximum adsorption efficiency achieved for of Y(Ⅲ) by nFeS was 81.2 % compared to only 38.7 % for Eu(Ⅲ) and 20.8 % for Mn(Ⅱ), demonstrating that nFeS had a high selective adsorption for Y(Ⅲ). To understand the origins of the high selectivity of nFeS, the removal of REEs by the capping layer and the FeS-core were separately investigated. Specifically, given the hard and soft acid base principle (HASB) and the square antiprism coordination geometry of Y(Ⅲ), the adsorption of Y(Ⅲ) by the capping layer was predominantly attributed to CO and –NH2 serving as a monodentate ligand to strongly chelate with Y(Ⅲ), while Y(Ⅲ) interacted with Fe–O on the FeS-core and –COOH more via ion-exchange with Y(Ⅲ). Collectively, cooperative interactions between the capping layer and FeS-core resulted in the overall highly selective adsorption of Y(Ⅲ) by nFeS, suggest this approach has significant potential for future practical remediation and recovery applications to Y(Ⅲ) rich mining wastewaters.

Cation-cation interaction in Np(V) o-chlorobenzoate complexes with 1,10-phenanthroline and 2,2′-bipyridine

Two new Np(V) o-Cl-benzoates of composition [(NpO2)(phen)(C7H4ClO2)]3 (1) and [(NpO2)(bipy)(C7H4ClO2)]4·2H2O (2) with N-donor ligands phenantroline (phen) and bipyridine (bipy) have been synthesized and structurally characterized. In these complexes, NpO2+ cations are linked by cation-cation bonds, acting as monodentate ligands with respect to each other. As a result, a trimeric complex is formed in 1, and a tetrameric complex is formed in 2. The Np atoms in both compounds have a pentagonal-bipyramidal environment with “yl” oxygen atoms in apical positions. The equatorial planes of the bipyramids are formed by two nitrogen atoms of phen (1) or bipy (2), one oxygen atom of another NpO2+ cation, and two oxygen atoms from two C7H4ClO2– anions. Electronic absorption spectra of crystalline compounds were measured in the near IR-visible range.

Synthesis, X-ray Structures and Hirshfeld Analysis of Two Novel Thiocyanate-Bridged Ag(I) Coordination Polymers

Two novel silver(I) coordination polymers, [Ag(4BP)(SCN)]n (1) and {(4BPH)+[Ag(SCN)2]−}n (2) (4BP = 4-benzoyl pyridine), have been synthesized. The two complexes were prepared using almost the same reagents, which were AgNO3, 4BP and NH4SCN. The only difference was the presence of 1:1 (v/v) HNO3 in the synthesis of 2. In the two complexes, the Ag(I) has distorted tetrahedral coordination geometry. The structure of both complexes and the involvement of the thiocyanate anion as a linker between the Ag(I) centers were confirmed using single-crystal X-ray diffraction. 4BP participated as a monodentate ligand in the coordination sphere of complex 1, while in 2 it is found protonated (4BP-H)+ and acts as a counter ion, which balances the charge of the anionic [Ag(SCN)2]− moiety. The thiocyanate anion shows different coordination modes in the two complexes. In complex 1, the thiocyanate anion exhibits a µ1,1,3 bridging mode, which binds three Ag(I) ions to build a boat-like ten-membered ring structure leading to a two-dimensional coordination polymer. In 2, there are mixed µ1,1 and µ1,3 bridging thiocyanate groups, which form the one-dimensional polymeric chain running in the a-direction. Several interactions affected the stability of the crystal structure of the two complexes. These interactions were examined using Hirshfeld surface analysis. The coordination interactions (Ag-S and Ag-N) have a great impact on the stability of the polymeric structure of the two complexes. Additionally, the hydrogen-bonding interactions are crucial in the assembly of these coordination polymers. The O…H (10.7%) and C…H (34.2%) contacts in 1 as well as the N···H (15.3%) and S···H (14.9%) contacts in 2 are the most significant. Moreover, the argentophilic interaction (Ag…Ag = 3.378 Å) and π- π stacking play an important role in the assembly of complex 2.

Synthetic Approaches towards Peptide‐Conjugates of Pt(II) Compounds with an (O,S) Chelating Moiety

AbstractMetal‐containing peptide (bio−)conjugates have received continuous interest due to their enormous potential for bioinorganic and medicinal research. In many bioconjugates the chemical inertness of the metal‐containing units facilitates synthesis e. g. by copper‐catalyzed alkyne−azide cycloaddition or the formation of peptide bonds. However, when the metal complex contains labile ligands, which are often critical to their biological activity, the synthetic proceeding requires careful planning. Here, we report on the synthesis of a set of peptide bioconjugates with a platinum(II) core, coordinated through widely variable (O,S) chelating β‐hydroxydithiocinnamic ester and two monodentate ligands. We have evaluated the synthetic applicability of metal−peptide bioconjugation techniques between the model peptide Leu5−enkephalin and differently functionalized (O,S)Pt units. Within this, the type and position of anchor used at the β‐hydroxydithiocinnamic unit proved to be crucial for success, but equally important was the synthetic order of conjugation and complexation. In this work, synthetic approaches for the linkage of metal complexes that are coordinated by functionalized ligands towards peptides were explored. Two general methods to link the studied (O,S)Pt pharmacophore to the model peptide, Leu5−enkephalin, have been applied, namely the most prominent “click” reaction, CuAAC, and the linking via amide bonds. Overall, it could be shown that the structural motif of the (O,S)Pt compounds presented here offers multiple possibilities of derivatization, so that bioconjugation towards peptides can be made possible. Depending on the demands made on the resulting metal bioconjugate, both the dithioester and the aromatic unit of β‐hydroxydithiocinnamic esters can be used as anchor for peptides. However, from our results here, it can be concluded that anchoring at the aromatic subsite seems preferable from a synthetic point of view as the spatial distance of the reactive terminal functional group (alkyne or azide) to the metal center may avoid intramolecular reactions. Also, for using azide−alkyne click chemistry as a conjugation strategy, the (O,S) unit should contain the azide function and not the alkyne function, as triple bond hydration may occur. Classical amide‐bond conjugation also proved to be a suitable method in our hands when performed in solution. A coupling of the β‐hydroxydithiocinnamic unit to resin‐bound peptide would not be possible due to the typically harsh cleavage conditions.

Kinetics, equilibrium, and computational study on the monomerization reaction of {CH3ReVO(pdt)}2 dimer with monodentate ligands

The monomerization reaction of {MeReO(pdt)}2 dimer (the pdt is 1,3-propanedithiolate) with monodentate ligand has been studied experimentally:{MeReO(pdt)} + 2 L ⇌ 2 MeReO(pdt)L and L is a monodentate ligand presented in Figure 1. No monomerization reaction have been observed with the indazole and diphenyl sulfides, and 2-methylpyridne. For the 2-methylpyridne case, the no reaction was observed because of the steric effect of the methyl group at the ortho position prevent the nitrogen from coordination. But the phosphines and pyridines derivatives monomerize the dimer. The rate law is given by ν = (ka[L] + kb [L]2) {MeReO(pdt)2} for ligands 1 to 4 in Table 1 and the rate law is ν = kb [L]2 {MeReO(pdt)2} for ligands 6 to 8 in Table 1. The equilibrium constant of the same reaction has been also evaluated. The rate constant (k) and the equilibrium constant (Keq) values correlate well with the basicity of the ligand. The reaction constant (ρ) is -4.9 and -1.3 for pyridine and phosphine, respectively, obtained from Hammett correlation with σ. The computational study on I1 and I2 intermediates (Scheme 3) shows that these intermediates are not plausible intermediates as previously proposed1, 2. These results are attributed to the high angle strain on the bridging sulfur that prevent the formation of the I1 and I2 intermediates and the reaction proceed through different intermediates (I3 and Ia Scheme 4). Therefore, the proposed mechanism is modified to accommodate the computational results.

Metal-Organodiphosphonate Chemistry: Hydrothermal Syntheses and Structures of Two Novel Copper(II) Coordination Polymers with o-Xylylenediphosphonic Acid and 4,4′-Bipyridine Ligands

Abstract Two novel copper organodiphosphonates, namely [Cu4(L)2(H2O)4]n (MOF 1) and [Cu4(bpy)(HL)2(OH)2]n•2nH2O (MOF 2), (where H4L = o-xylylenediphosphonic acid and bpy = 4,4′-bipyridine), have been synthesized as a result of changing the pH values (Initial pH: 3.50 for MOF 1 and pH: 6.00 to 3.50 for MOF 2) under hydrothermal conditions. Coordination polymers were characterized by elemental analysis, infrared spectroscopy, and single crystal X-ray diffraction analysis. MOFs 1 and 2 crystalize in the orthorhombic Pna21 and triclinic P$\bar{1}$ space groups, respectively. The organophosphates acted as multidentate bridging ligands in both compounds to link copper ions into a framework. From the analysis of magnetic susceptibility measurements between 1.8 to 300 K, all the Cu valences were confirmed to be 2+, and antiferromagnetic interactions were characterized. The adsorption properties of MOFs 1 and 2 as well as known [Cu3(HL)2]n, [Cu(SO4)(bpy)(H2O)3]n•2nH2O, and [Cu(SO4)(bpy)(H2O)3]n•2nH2O have also been investigated with mono- and divalent dyes including Bromophenol Blue and Orange G as a pollutant removal model.

Four Redox Isomers of a [3 × 3] Copper-Iron Heterometal Grid.

A mixed-valence heterometallic nonanuclear [3 × 3] grid complex, [CuI2CuII6FeIII(L)6](BF4)5·MeOH·9H2O (1; MeOH = methanol), was synthesized by a one-pot reaction of copper and iron ions with multidentate ligand 2,6-bis[5-(2-pyridinyl)-1H-pyrazol-3-yl]pyridine (H2L). 1 showed five quasi-reversible one-electron redox processes centered at +0.74, +0.60, +0.39, +0.27, and -0.13 V versus SCE, assignable to four CuI/CuII processes and one FeII/FeIII couple, respectively. The two-electron-oxidized species [CuII8FeIII(L)6](PF6)7·4MeOH·7H2O (12eOx), the two-electron-reduced species [CuI4CuII4FeIII(L)6](PF6)3·2H2O (12eRed), and the three-electron-reduced species [CuI4CuII4FeII(L)6](PF6)2·5MeOH·H2O (13eRed) were isolated electrochemically. The four redox isomers were characterized by single-crystal X-ray analysis, SQUID magnetometry, and Mössbauer spectroscopy.

Redox Activity of IrIII Complexes with Multidentate Ligands Based on Dipyrido-annulated N-Heterocyclic Carbenes: Access to High Valent and High Spin State with Carbon Donors.

Synthetic strategies to access high-valent iridium complexes usually requireuse of π donating ligands bearing electronegative atoms (e.g. amide or oxide) or σ donating electropositive atoms (e.g. boryl or hydride). Besides the η5-(methyl)cyclopentadienyl derivatives, high-valent η1 carbon-ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all-carbon-ligated anionic bis(CCC-pincer) IrIII complex. Being both σ and π donating, the diaryl dipyrido-annulated N-heterocyclic carbene (dpa-NHC) IrIII complex allowed a stepwise 4e- oxidation sequence. The first 2e- oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC-tetradentate ligand. A further 2e- oxidation allowed isolation of a high-valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon-ligated iridium complexes and demonstrate the electronic tuning potentialof organic π ligands for unusual electronic properties.