The oxygen evolution reaction (OER) of water splitting is essential to electrochemical energy storage applications. While nickel electrodes are widely available heterogeneous OER catalysts, homogeneous nickel catalysts for OER are underexplored. Here we report two carbene-ligated nickel(II) complexes that are exceptionally robust and efficient homogeneous water oxidation catalysts. Remarkably, these novel nickel complexes can assemble a stable thin film onto a metal electrode through poly-imidazole bridges, making them supported heterogeneous electrochemical catalysts that are resilient to leaching and stripping. Unlike molecular catalysts and nanoparticle catalysts, such electrode-supported metal-complex catalysts for OER are rare and have the potential to inspire new designs. The electrochemical OER with our nickel-carbene catalysts exhibits excellent current densities with high efficiency, low Tafel slope, and useful longevity for a base metal catalyst. Our data show that imidazole carbene ligands stay bonded to the nickel(II) centers throughout the catalysis, which allows the facile oxygen evolution.

A new Zn(II) coordination polymer based on -phthalato (Phth) and 2-aminopyridine (2-Ampy) viz. {[Zn(2Ampy)(Phth)]∙(HO)]} () has been synthesized at room temperature and characterized by elemental analyses, electronic spectroscopy, FTIR spectroscopy, thermal analysis (TGA/DSC), powder Xray diffraction (PXRD) and single crystal Xray diffraction. The basic trimeric units of form a polymeric chain by N-H⋯O and π⋯π interactions. These polymeric chains interconnect through various non-covalent interactions in two perpendicular directions to ultimately give rise to a 3D architecture of . The interesting non-covalent interactions in , contributing to its stability in the solid state are studied by Hirshfeld surface analysis and other different theoretical tools. Molecular docking study of is performed against six different proteins of SARS-CoV-2. The drug potential of the synthesized compound is evaluated by ADMET calculations.

Three new mixed-ligand copper(II) complexes (-) with NN'O type unsymmetrical tridentate Schiff base ligands and -donor heterocyclic co-ligands, with general formula [Cu(SB)(L)]ClO, were synthesized and characterized using single crystal x-ray diffraction (SCXRD), FT-IR and UV-Vis spectroscopy and elemental analyses. The SB ligand is the half-unit form of the condensation of 1,3-propanediamine with 5-methoxysalicylaldehyde and the co-ligands (L) are pyridine (py in ), 2,2'-bipyridine (bpy in ) and 1,10-phenanthroline (phen in ). Crystal structures of and were obtained by SCXRD. Molecular docking and pharmacophore studies were performed to study the interactions between the synthesized complexes and SARS-CoV-2 virus main proteases (PDB IDs: 6LU7, 6WQF and 6W9C). Results revealed that complex with phen co-ligand showed better docking scores with the three receptors, i.e. 6LU7 (-8.05 kcal.mol), 6W9C (-7.70 kcal.mol) and 6WQF (-7.75 kcal.mol). The order of the binding best energies for was also as follows: 6LU7 > 6WQF > 6W9C. All of the studied complexes showed considerable performance, comparable to the standard drug, Favipiravir.

The global coronavirus (COVID-19) outbreak has prompted scientists to discover a cure for the disease. So far, phosphorus-based drugs have been proposed. These drugs have good inhibitory activity against the main protease (Mpro). Hence, in order to introduce a group of inhibitors the coronavirus, 51 compounds containing different mono, bis, and tetra phosphonates as Remdesivir derivatives, 32 of which are new, were synthesized and characterized by P, C, and H NMR and IR spectroscopy. Their biological activities were also investigated by Molecular Docking, QSAR, and Pharmacophore. Van der Waals, hydrogen bonding, and hydrophobic interactions were studied for all compounds as well as binding energy (△G, Kcal/mole) and the inhibitory constant Ki (μM) obtained by Molecular Docking. The results showed that the topology of the ligands and the change of the different groups attached to them can be effective in the placement position in the active site of the enzyme (Glu 166 and Gln 189). And bisphosphonates have a high interaction tendency with Mpro COVID-19. Compound L24 was identified as the best inhibitor with the -6.38 kcal/mol binding energy. The quantitative structure-activity relationship (QSAR) findings demonstrated that the polarity and topology of molecules in all phosphonate derivatives were important parameters affecting the effecting on the binding energy and inhibitory ability of compounds. The DFT and pharmacophore results are in good accordance with those of QSAR and molecular docking. This study can be helpful to gain a better understanding of the interactions between the Mpro of virus and its inhibitors in order to attain drugs with more effect on coronavirus (COVID-19).

A series of air-stable trigonal bipyramidal Fe complexes supported by a redox non-innocent NNN pincer ligand, Cz (Pyr) (R = Pr, Me, or H), were synthesized, fully characterized, and utilized for the investigation of the interaction between acetone and the Fe center. The magnetic moments determined from the paramagnetic H NMR spectra in conjunction with EPR and Mössbauer spectroscopy indicate the presence of a high-spin ferric center. Cyclic voltammetry studies feature two quasi-reversible events corresponding to a metal-centered Fe reduction around -0.40 V (vs. Fc) and a ligand-centered Cz (Pyr)/Cz (Pyr) oxidation at potentials near +0.70 V (vs. Fc). UV-Visible spectroscopy in CHCl showcases ligand-metal charge transfer (LMCT) bands, as well as coordination of acetone to Cz (Pyr)FeCl. In situ IR spectroscopy and solution conductivity (κ) measurements of Cz (Pyr)FeCl with varied equivalents of acetone reveal that acetone is weakly associated with the iron center.

The remarkable catalytic transformation of CO to liquid hydrocarbons by Fe and Co catalysts in the industrial Fischer-Tropsch process motivates interest in developing well-defined systems to model aspects of this chemistry. One of the most interesting potential intermediates in this chemistry is a terminally-bound, first row metal carbide, yet a molecular model of this species remains elusive. With this in mind, we targeted the synthesis of highly-activated Fe-thiocarbonyl complexes, as prospective precursors to S-functionalization, C-S bond cleavage, and carbide generation. Herein, we describe the synthesis of three Fe-CS complexes that can be alkylated to generate a series of terminal Fe-carbynes that could be characterized across three oxidation states. Strategies to access C-S bond scission from these species are discussed, including limitations that, thus far, have precluded the generation of a terminal Fe-carbide for this system.

Multimetallic redox cooperativity features heavily in both bioinorganic and synthetic reactions. Here, the electronic structure of the bimetallic Ti/Ti complex , [(CpTi)(OCTMS)] has been revisited with EPR, confirming a predominantly Ti/Ti electronic structure. Reactions of with 2,6-dimethylphenyl isocyanide (CNXyl), TMSCl, MeI, and BnCl were explored, revealing differential redox chemistry of the bimetallic core. In reactions with CNXyl and TMSCl, the metallacyclic Ti center remained unperturbed, with reactions taking place at the pendent κ(O,O)-titanocene fragment, while reaction with MeI resulted in remote oxidation of the metallacyclic Ti center, indicative of a cooperative redox process. All structures were studied via X-ray diffraction and EPR spectroscopic analysis, and their electronic structures are discussed in the context of the covalent bond classification (CBC) electron counting method.

Municipal and residential water purification rely heavily on activated carbon (AC), but regeneration of AC is costly and cannot be performed at the point-of-use. Clay minerals (CMs) comprise a class of naturally abundant materials with known capacities for analyte adsorbance. However, the gel-forming properties of CMs in aqueous suspension pose problems for these materials being used in water-purification. In this study, we have taken three main steps to optimize the use of CMs in these applications. First, we produced several variants of montmorillonite CMs to evaluate the effect of interstitial cation hydrophobicity on the ability of the CM to uptake chargecarrying organic pollutants. These variants include CMs with the following cations: sodium, hexyl(triphenyl) phosphonium, hexyadecyl(triphenyl)phosphonium, and hexyl(tributyl)phosphonium. Second, we synthesized polymer-clay mineral composite films composed of polyvinyl alcohol (PVA), crosslinked in the presence of a CM variant. These films were evaluated for their ability to uptake malachite green (MG). Finally, we developed a one-pot synthetic method for the generation of polymer-clay particles for use in a continuous column process. We synthesized polymer-clay mineral particles using the highest performing CM (based on the film experiments) and evaluated the equilibrium capacity and kinetics of MG uptake from solution.

An EPR signal for Mn(III) bound to the metal transport protein transferrin has been detected for the first time. The temperature dependence and simulations of the EPR signal are consistent with the Mn(III) centers being six-coordinate in an elongated tetragonal environment. Thus, the incorporation of Mn(III) within the Tf active site does not vastly alter the coordination number or active site geometry relative to native Fe(III)-Tf. This parallel mode EPR signal for Mn(III)-Tf could prove valuable for future studies aimed at determining the physiological relevance of Mn(III)-Tf.

A series of 2,6-diiminopyridine-derived macrocyclic ligands have been synthesized via [2+2] condensation around alkaline earth metal triflate salts. The inclusion of a -butyl group at the 4-position of the pyridine ring of the macrocyclic synthons results in macrocyclic complexes that are soluble in common organic solvents, thereby enabling a systematic comparison of the physical properties of the complexes by NMR spectroscopy, mass spectrometry, solution-phase UV-Vis spectroscopy, cyclic voltammetry and single-crystal X-ray crystallography. Solid-state structures determined crystallographically demonstrate increased twisting in the ligand, concurrent with either a decrease in ion size or an increase in macrocycle ring size (18, 20, or 22 membered rings). The degree of folding and twisting within the macrocycle can be quantified using parameters derived from the N-M-N bond angle and the relative orientation of the pyridinediimine (PDI) and pyridinedialdimine (PDAI) fragments to each other within the solid state structures. Cyclic voltammetry and UV-Vis spectroscopy were used to compare the relative energies of the imine π* orbital of the redox active PDI and PDAI components in the macrocycle when coordinated to redox inactive metals. Both methods indicate the change from a methyl to hydrogen substitution on the imine carbon lowers the energy of the ligand π* system.

We report iridium catalysts IrCl(η-Cp*)(κ-(2-pyridyl)CHNSOCHX) (, X = CH and , X = F) for transfer hydrogenation of ketones with 2-propanol that operate by a previously unseen metal-ligand cooperative mechanism. Under the reaction conditions, complexes ( and ) derivatize to a series of catalytic intermediates: Ir(η-Cp*)(κ-(CHN)CHNSOAr) (), IrH(ηCp*)(κ-(2-pyridyl)CHNSOAr) (), and Ir(η-Cp*)(κ-(2-pyridyl)CHNSOAr) (). The structures of and were established by single-crystal X-ray diffraction. A rate-determining, concerted hydrogen transfer step ( + RCHOH ⇄ + RCO) is suggested by kinetic isotope effects, Eyring parameters (Δ = 29.1(8) kcal mol and Δ = -17(19) eu), proton-hydride fidelity, and DFT calculations. According to DFT, a nine-membered cyclic transition state is stabilized by an alcohol molecule that serves as a proton shuttle.

The synthesis of the metalloligand Ta(κ-NP)Cl (NP = 2-diphenylphosphinopyrrolide) and its coordination chemistry with group 9 and 10 metals is reported. Treatment of Ta(κ-NP)Cl with group 9 and 10 metals resulted in clean formation of the heterobimetallic complexes ClTa(μ-NP)M (M = Ni (), Pd ()) or ClTa(μ-NP)MCl (M = Rh (), Ir ()). Each pair of complexes is isostructural and contains three phosphinopyrrolide ligands that bridge the metal centers. The d or d complexes are all diamagnetic and X-ray crystallographic analysis reveals similarly short metal-metal distances, ranging from 2.2979(5) Å to 2.4366(2) Å. Despite the similar bonding metrics in -, treatment with an L type donor (2,6-dimethylphenylisocyanide (CNXylyl)) reveals 3 different coordination geometries in TaNi(CNXylyl) (), TaPd(CNXylyl) (), and TaIr(CNXylyl) (). While complexes , , and all bind the isocyanide at the late metal, ligand rearrangements are observed in the first row complex . Complex binds the isocyanide in the axial position while equatorial binding is observed in . All isocyanide adducts maintain close metal-metal contacts in the solid state.

Bidentate chelators 1-(1-benzyl-1,2,3-triazol-4-yl)isoquinoline and 3-(1-benzyl-1,2,3-triazol-4-yl)isoquinoline were prepared from benzyl bromide and trimethylsilylethynylisoquinoline precursors using a tandem deprotection/substitution/CuAAC synthetic approach. Each chelator is capable of forming a stable 3:1 Ru(II) coordination compound, which forms as a geometric isomer mixture. These Ru(II) complexes possess unique MLCT absorbance signatures at 450/472 nm (1-isomer) and 367 nm (3-isomer) relative to their constituent chelating units. Minimum inhibitory concentration values as low as 0.4 μM are observed for Ru(II) complexes against representative Gram-positive bacteria and . Comparing the MIC values of these isoquinoline compounds with analogous 2-(1-benzyl-1,2,3-triazol-4-yl)pyridine compounds shows a 2.5- to 40-fold improvement in potency. This study establishes that increased hydrophobicity introduced at the central chelating units of Ru(II) coordination compounds can be a useful means by which to optimize antimicrobial activity that is complimentary to the variation of peripheral substituent identity at the chelator's N1 triazole position.

Low-coordinate ions possess exciting magnetic, optical, and reactive properties that may afford novel material physics. Hence, it is important to test both synthetic methods for realizing extended solids of such ions as well as the properties of smaller molecular fragments of envisioned future materials. Herein, we report the synthesis and characterization of a new dinuclear Fe species, [{(MeSi)N}Fe{--{HN(SiMe)}(CMe){N(SiMe)}}Fe{N(SiMe)}] (), formed through a transamination reaction between [Fe{N(SiMe)}] and the bulky diamine -{HN(SiMe)}(CMe) (). The Fe centers of this dimer assume a pseudo-trigonal-planar, three-coordinate conformation in , bridged by two aromatic diamines. Single-crystal X-ray diffraction, IR spectroscopy, and Mössbauer spectroscopy enable the assignment of both Fe centers as the 2+ oxidation state. Magnetic studies show that displays a weak antiferromagnetic exchange interaction ( = -2.33 cm) and moderate zero-field splitting ( = 7.51 cm). Importantly, these studies demonstrate the viability of using transamination to bridge high-spin low-coordinate metal ions and hence the technique may, in the future, produce new extended structures.

Cyclometalated rhodium(III) and iridium(III) complexes () of two Schiff base ligands and with the general formula [M(ppy)(L)]Cl {M = Rh, Ir; ppy = 2-phenylpyridine; = 1, 2; L = Schiff base ligand} have been synthesized. The new ligands and the complexes have been characterized with spectroscopic techniques. Electrochemistry of the complexes revealed anodic behavior, corresponding to an M(III) to M(IV) oxidation. The X-ray crystal structures of complexes and have also been determined to interpret the coordination behavior of the complexes. Photophysical study shows that all the complexes display fluorescence at room temperature with quantum yield of about 3 × 10 to 5 × 10. The electronic absorption spectra of all the complexes fit well with the computational studies. Cellular imaging studies were done with the newly synthesized complexes. To the best of our knowledge, this is the first report of organometallic complexes of rhodium(III) and iridium(III) with Schiff base ligands explored for cellular imaging. Emphasis of this work lies on the structural features, photophysical behavior, cellular uptake and imaging of the fluorescent transition metal complexes.

A total of 44 bis-aryl-monocyclic polyamines, monoaryl-monocyclic polyamines and their transition metal complexes were prepared, chemically characterized, and screened in vitro against the promastigotes, axenic amastigotes and intracellular amastigotes in THP1 cells. The IC and/or IC values showed that 10 compounds were similarly active at about 2-fold less potent than known drug pentamidine against promastigotes. The most potent compound had an IC of 2.82 μM (compared to 2.93 μM for pentamidine). Nine compounds were 1.1-13.6-fold more potent than pentamidine against axenic amastigotes, the most potent one being about 2-fold less potent than amphotericin B. Fourteen compounds were about 2-10 fold more potent than pentamidine, the most potent one is about 2-fold less potent than amphotericin B against intracellular amastigotes in THP1 cells. The 2 most promising compounds (FeCl and MnCl), with strong activity against both promastigotes and amastigotes and no observable toxicity against the THP1 cells are the Fe- and Mn- complexes of a dibenzyl cyclen derivative. Only 2 of the 44 compounds showed observable cytotoxicity against THP1 cells. Tetraazamacrocyclic monocyclic polyamines represent a new class of antileishmanial lead structures that warrant follow up studies.

The reactions of 1-methyl-1,3-dihydro-2-benzimidazole-2-selone, H(sebenzim), towards the zinc and cadmium halides, MX (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzim)]MX, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N-H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzim)]ZnX and [H(sebenzim)]CdX (X = Cl, Br), exhibit two intramolecular N-H•••X interactions, whereas the iodide derivatives, [H(sebenzim)]ZnI and [H(sebenzim)]CdI, exhibit only one intramolecular N-H•••I interaction. Comparison of the M-Se and M-Cl bond lengths of the chloride series, [H(sebenzim)]MCl (M = Zn, Cd, Hg), indicates that while the average M-Cl bond lengths progressively increase as the metal becomes heavier, the variation in M-Se bond length exhibits a non-monotonic trend, with the Cd-Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzim)]CdCl, [H(sebenzim)],CdCl•[H(sebenzim)]CdCl, which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI and H(sebenzim) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzim)]-[H(benzim)]CdI, a transformation that is associated with cleavage of the C-Se bond.

Homoleptic iron-alkyl complexes have been implicated as key intermediates in iron-catalyzed cross-coupling with simple iron salts. Tetraalkyliron(III) ferrate species have been shown to be accessible with either methyl or benzyl ligands, where the former complex is = 3/2 and distorted square planar while the latter is a = 5/2 distorted tetrahedral species. In the current study, a new tetraalkyliron(III) complex is synthesized containing modified methylene substituents that incorporate large trimethylsilyl (TMS) groups to further probe steric and electronic ligand effects in tetraalkyliron(III) complexes by increasing the electron-donating ability of the ligand while retaining steric bulk. Detailed structural and DFT studies provide insight into electronic structure and bonding of the four-coordinate trimethylsilylmethyl iron(III) complex compared to the previously reported analogs containing methyl and benzyl ligands.

Crown ethers are useful macrocycles that act as size-selective binding sites for alkali metals. These frameworks have been incorporated into a number of macromolecular assemblies that use simple cations as reporters and/or activity triggers. Incorporating crown ethers into secondary coordination sphere ligand frameworks for transition metal chemistry will lead to new potential methods for controlling bond formation steps, and routes that couple traditional ligand frameworks with these moieties are highly desirable. Herein we report the syntheses of a family of tridentate phosphine complexes bearing tethered aza-crown ethers (lariats) designed to modularize the variation of aza-crown size, lariat length, and distal phosphine substituents, followed by the synthesis and solid-state structures of Mo(III) complexes bearing cations in the pendent crown ethers.

A series of -NHC pincer complexes of palladium(II) have been prepared and characterized. These pyridyl-spaced dicarbene complexes ( ) were synthesized with substituents of varying steric bulk at the wingtip positions, which include R = methyl, ethyl, isopropyl, cyclohexyl, mesityl and 2,6-diisopropylphenyl. The synthesis of this library of complexes was accomplished either by direct metallation of the prerequisite pyridyl-spaced -imidazolium proligands with Pd(OAc) or via treatment with AgO to afford the corresponding silver carbenes, which were then transmetallated onto palladium. Solid-state structures for each of the derivatives were obtained via X-ray crystallography and allowed for the steric properties of each PDC ligand to be evaluated by two methods. These analyses, which included calculation of the percent buried volume (%V) and solid angles of the PDC ligands, served to characterize the steric environment around the palladium center in each of the complexes that was prepared. Finally, voltammetry and controlled potential electrolysis studies were performed to characterize the redox chemistry of the derivatives and assess if they could electrocatalyze the reduction of CO. The influence of the steric properties of the PDC ligand on the electrochemistry of the resulting complexes is also discussed.

The preparation and characterization of two Ni complexes are described, a terminal Ni-OH complex with the tripodal ligand tris[(N)-tertbutylureaylato)-N-ethyl)]aminato ([Hbuea]) and a terminal Ni -OH complex with the tripodal ligand ,',″-[2,2',2″-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido) ([MST]). For both complexes, the source of the -OH and -OH ligand is water. The salts K[NiHbuea(OH)] and NMe[NiMST(OH)] were characterized using perpendicular-mode X-band electronic paramagnetic resonance, Fourier transform infrared, UV-visible spectroscopies, and its electrochemical properties were evaluated using cyclic voltammetry. The solid state structures of these complexes determined by X-ray diffraction methods reveal that they adopt a distorted trigonal bipyramidal geometry, an unusual structure for 5-coordinate Ni complexes. Moreover, the Ni-OH and Ni-OH units form intramolecular hydrogen bonding networks with the [Hbuea] and [MST] ligands. The oxidation chemistry of these complexes was explored by treating the high-spin Ni compounds with one-electron oxidants. Species were formed with S = 1/2 spin ground states that are consistent with formation of monomeric Ni species. While the formation of Ni-OH complexes cannot be ruled out, the lack of observable O-H vibrations from the putative Ni-OH units suggest the possibility that other high valent Ni species are formed.