Coordination Geometry Research Articles

Effect of B-site cationic substitution on the structural, spectroscopic, and conductivity behaviour of Ho2(Hf1-xZrx)2O7 (x=0 and 1)

Ideally, a solid electrolyte which is a central component of SOFC should exhibit high anionic or cationic ionic conductivity at the proposed operating temperatures. In most cases, the performance is compromised when operating above 1000 °C due to poor mechanical, thermal and chemical stability of selected functional and non-functional materials. In this context, pyrochlores are one of the potential candidates due to their high conductivity, flexibility to accommodate large cations, and high mechanical, thermal and chemical stability. In this study, we report the synthesis of nano-powders of Ho2Hf2O7 (HH) and Ho2Zr2O7 (HZ) pyrochlore ceramics by eco-friendly alginate mediated ion-exchange process also known as Leeds Alginate Process (LAP) and provide further insight into the structure - conductivity relationship of HH and HZ compounds by EXAFS studies. Both the compositions were sintered at temperatures, ranging from 1100 °C-1500 °C at 2 h dwell time to achieve the desired high-density ceramic with stable pyrochlore structure. X-ray diffraction and Extended X-ray absorption fine structural (EXAFS) analysis showed superlattice reflections and complex coordination geometry of these oxides. The coordination number and disorder factor in the case of HZ were found to be more stable than the HH sample, as evident from the EXAFS. Impedance spectroscopy and dc-conductivity analysis showed a better charge transport behavior in HZ ceramics than in HH making HZ as a preferred solid electrolyte for SOFC. The conductivity of Ho2Zr2O7 is comparable with the best-known fluorite oxide-ion conductor such as Sc2O3-stabilized ZrO2 at 500 °C.

Enhanced Catalytic Activity of a Copper(II) Metal-Organic Framework Constructed via Semireversible Single-Crystal-to-Single-Crystal Dehydration.

Herein, we present a copper(II) metal-organic framework, [Cu2(btec)(OH2)4]·2H2O (1) [(btec)4- = 1,2,4,5-benzenetetracarboxylate], that undergoes single-crystal-to-single-crystal transformations into two anhydrous phases 2' and 2″ with the chemical formula [Cu2(btec)], triggered by two-step dehydration at 403 and 433 K, respectively. After immersion in water for 3 days at room temperature, 2' transformed into [Cu2(btec)(OH2)] (3), while both 2' and 2″ took 1 week to revert to 1. Dynamic vapor sorption studies validated water-induced reversible structural transformations at 70% relative humidity (RH). According to single-crystal X-ray diffraction (SC-XRD), the local coordination geometry of the Cu2+ ion in 2' changed from a saturated octahedron to a coordinatively unsaturated square-based pyramid in 3, manifested by changes in color and dimensionality. From a topological point of view, all of the scaffolds show a binodal (3,6)-connected kgd topology with the point symbol {43}2{46}. In addition, the materials were thoroughly characterized using routine spectroscopic data and various analytical techniques. The catalytic activity of the microporous materials in the liquid-phase oxidation of styrene in acetonitrile, using 30% (wt) H2O2 as the oxidant, was investigated. The excellent performance of the monohydrous phase 3 was shown to be superior to the pristine framework and the anhydrous counterparts, as evidenced by a good turnover number (TON) and turnover frequency (TOF) = 82.6 and 21.0 h-1, respectively. Within 4 h, the substrates were catalytically oxidized to the desired products with up to 67% conversion and 100% benzaldehyde selectivity. It is worth noting that the accessible active metal sites and higher surface area enhanced the catalytic properties of 3. Furthermore, the maintenance of catalytic efficiency over five cycles and reusability are illustrated and discussed in terms of the structural differences of the microporous frameworks. Thus, a preliminary reaction mechanism for the selective oxidation of styrene is proposed. This study not only provides a fascinating example of MOF chromism achieved by thermal activation and rehydration but also sheds some light on the relationship between pore-surface- or metal-engineered sites in MOFs and their heterogeneous catalytic performances.

Crystal structures, phase transitions, thermodynamics, and molecular dynamics of organic–inorganic hybrid crystal [NH(CH3)3]2ZnCl4

Understanding the physical properties of organic–inorganic hybrid [NH(CH3)3]2ZnCl4 is necessary for its potential application in batteries and fuel cells due to its environmentally-friendly, and highly stable character. Here, we determine its overall properties in detail, such as its orthorhombic crystal structure, and phase transition temperatures associated with five different phases. Structural geometry was studied by the chemical shifts caused by the local field around 1H. No changes were observed for the environment around 1H for CH3, whereas the 1H chemical shifts around NH in the cation were shown due to the change in the hydrogen bond N‒H···Cl. This is related to the change in Cl around Zn in the anion. In addition, the coordination geometry of 14N and 1H around 13C exhibited increased symmetry at high temperatures. Finally, we were able to understand its molecular dynamics by the significant change with temperature observed from the spin–lattice relaxation time T1ρ values, which represent the energy transfer for the 1H and 13C atoms of the cation. The activation energies obtained from the T1ρ results were 3–4 times large at phase I (> 348 K) than at phase V and IV (< 286 K). The relaxations show that the energy barriers in phases IV and V are related to the reorientation of methyl groups around the triple symmetry axis, while the reorientation of methyl groups of the cation in phase I is related to as a whole.

Exploring the insights and benefits of biomass-derived sulfuric acid activated carbon for selective recovery of gold from simulated waste streams

The surging affluent in society, concomitant with increasing global demand for electrical and electronic devices, has led to a sharp rise in e-waste generation. E-wastes contain significant amounts of precious metals, such as gold, which can be recovered and reused, thus reducing the environmental impact of mining new metals. Selective recovery using sustainable and cost-effective materials and methods is therefore vital. This study undertook a detailed evaluation of low-cost biomass-derived activated carbon (AC) for selective recovery of Au from simulated e-waste streams. Utilizing high-performance synthesized H2SO4-AC, the adsorption mechanisms were explicated through a combination of characterization techniques, i.e., FE-SEM, BET, TGA, XRD, FTIR, XPS, and DFT simulations to conceptualize the atomic and molecular level interactions. Optimization of coordination geometries between model H2SO4-AC and anionic complexes revealed the most stable coordination for AuCl4- (binding energy, Eb = -4064.15 eV). The Au selectivity was further enhanced by reduction of Au(III) to Au(0), as determined by XRD and XPS. The adsorption reaction was relatively fast (∼5h), and maximum Au uptake reached 1679.74 ± 37.66 mg/g (among highest), achieved through adsorption isotherm experiments. Furthermore, a mixture of 0.5 M thiourea/1 M HCl could effectively elute the loaded Au and regenerate the spent AC. This study presents radical attempts to examine in detail, the synergistic effects of H2SO4 activation on biomass-derived ACs for selective recovery of Au from complex mixtures. The paper therefore describes a novel approach for the selective recovery of Au from e-wastes using multifunctional biomass-derived H2SO4-AC.

Computational Structural Assessment on the Stereochemistry of the Transition Metal Complex Formed by a Naphthalene-1,4-dione Based Ligand with Divalent Nickel

The purpose of this paper is elucidating the stereochemistry of a complex obtained by coordinating to divalent nickel a naphthalene-1,4-dione based chemical compound, namely N-(3-mercapto-naphthalene-1,4-dione-2-yl)nicotinamide. As this particular transition metal ion may lead to different coordination geometries and also tacking into account the fact that the organic ligand contains six heteroatoms, it seem to be worth clarifying denticity of the ligand, the coordination geometry (including stereoisomerism) and, of course, what are the atoms involved into the coordination process. The study has been conducted by computational means, followed by quantum-chemical calculations and comparative interpretation of the UV-Vis spectra of both the ligand and the complex compound, in order to find out in which case the structural assessment is consistent with the electronic transitions exhibited whithin the spectra, i.e. which of the several theoretical coordination posibilities is the actual one. This investigation leads to the conclusion that the organic compound acts as a bidentate ligand and, moreover, the complex compound has a square-planar coordination geometry, the two heteroatoms through which the coordination is realized being the sulfur atom and the nitrogen atom directly bonded to the naphthalene-1,4-dione heterocycle. This is an important achievement, as the properties of the complex compound � including its biologic activity - are obviously related to the coordination manner.

Effects of changing ions on the crystal design, non-covalent interactions, antimicrobial activity, and molecular docking of Cu(II) complexes with a pyridoxal-hydrazone ligand.

The present work reports the influence of the presence of different ions (Cl-, Br-, NO3 -, or SO4 2-) on the formation and proprieties of Cu(II) complexes with pyridoxal-benzoylhydrazone (PLBHZ). Four new complexes were successfully synthesized, [CuCl2(PLBHZ)] (1), [CuBr2(PLBHZ)] (2), [CuCl(PLBHZ)H2O]⋅NO3⋅H2O (3), and [CuSO4(PLBHZ)H2O]⋅3H2O (4), and characterized by spectroscopic and physicochemical methods. A single-crystal X-ray study reveals the Schiff base coordinated to the metal center tridentate by the ONS-donor system, resulting in distorted square pyramidal coordination geometries. Noncovalent interactions were investigated by 3D Hirshfeld surface analysis by the d norm function, 2D fingerprint plots, and full interaction maps. The ion exchange is important in forming three-dimensional networks with π⋅⋅⋅π stacking interactions and intermolecular hydrogen bonds. The in vitro biological activity of the free ligand and metal complexes was evaluated against Gram-positive and Gram-negative bacterial strains and the free pyridoxal-hydrazone ligand showed higher activity than their Cu(II) complexes. Molecular docking was used to predict the inhibitory activity of the ligand and complexes against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria.

Synthesis, Characterization, Single Crystal XRD, Solid State Assembly Inspection by Hirshfeld Surface Analysis, and Theoretical Studies of Pb(II) complex with Thiourea Derivative

The current work describes the synthesis of a new Pb(II) complex Pb[ROMLIP]2 with a thiourea derivative. The synthesized complex was characterized by FT-IR, elemental analysis, and single crystal X-ray diffraction (XRD) analysis. The spectroscopic data confirmed that the thiourea ligands coordinate with the Pb center in a way that forms a dimeric structure with a distorted square pyramidal coordination geometry. Hirshfeld surface analysis was used to elaborate on the numerous intermolecular interactions responsible for the stabilization of the supramolecular assembly of the complex. Voids analysis was used to predict the crystal response to an applied stress. Geometry optimization of the synthesized complex was also explored through density functional theory (DFT) analysis. The structural parameters obtained through the DFT study at B3LYP/6-311g(d,p) level of theory with basis set 6-311G(d,p) are in good match with X-ray diffraction analysis. Additionally, the electronic energy band gap of the prepared complex was explored, which revealed the electronic transition during excitation from the ground state to the excited state.

A study of multibeam line measurement based on analytic geometry and genetic algorithm

This paper focuses on the multibeam bathymetry technology for seabed terrain detection, and utilizes the geometric model, genetic algorithm to study the multibeam bathymetry line according to the actual situation of multibeam bathymetry coverage width, measurement length and overlap rate. Firstly, this paper uses the geometric analysis of the coverage width in relation to the slope angle and seawater depth , establishes the multibeam bathymetry coverage width and overlap rate model, and obtains the results of the coverage width and overlap rate in the specified cases by using python. Secondly, on this basis, a new condition of line direction angle is introduced to establish a multibeam bathymetry coverage width model based on line direction, and the coverage widths under different line directions are obtained by using pyhon, and the analytical results show that the coverage widths and seawater depths are positively correlated with each other under the main oblique measurement direction. Finally, considering the influence of the minimum coverage area, the range of overlap rate and other constraints, the objective function of the shortest survey line length is established under the oblique measurement direction, and the shortest survey line program is obtained based on the genetic algorithm solution. The model constructed in this paper can provide a new idea in the field of nautical miles surveying and mapping.

(4-Butyl-1-ethyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane)rhodium(I) tetra-fluorido-borate.

In the title triazole-based N-heterocyclic carbene rhodium(I) cationic complex with a tetra-fluorido-borate counter-anion, [Rh(C8H12)(C8H15N3)(C18H15P)]BF4, which crystallizes with two cations and two anions in the asymmetric unit, the Rh center has a distorted square-planar coordination geometry with expected bond distances. Several nonclassical C-H⋯F hydrogen-bonding inter-actions help to consolidate the packing. Two of the F atoms of one of the anions are disordered over adjacent sites in a 0.814 (4):0.186 (4) ratio.

Solvent control of dimensionality in titanium aryloxide coordination polymers prepared from 4,4′-bis(hydroxyphenyl)sulfide

The crystal and molecular structures of three covalent metal–organic network (CMON) materials synthesized from titanium (IV) isopropoxide and the Bisphenol-A analog 4,4′-bis(hydroxyphenyl)sulfide in three different solvents have been determined. The structures of the one-dimensional chain coordination polymer [trans-Ti(μ-O:O’-OC6H4SC6H4O)2(C5H5N)2]n (1) obtained from pyridine and the two-dimensional sheet coordination polymer {[Ti2(μ-O:O’-OC6H4SC6H4O)2(μ2O:κO’-OC6H4SC6H4O)2(C4H8O)2]∙(C4H8O)y}n (2) from tetrahydrofuran both contain octahedral titanium (IV) coordination geometries, whereas the doubly interpenetrated three-dimensional coordination network [Ti2(μ-O:O’-OC6H4SC6H4O)2(μ2O:κO′-OC6H4SC6H4O)2]n (3) synthesized from benzene contains trigonal bipyramidal titanium (IV). Each material has been characterized by single crystal and powder X-ray diffraction, elemental analysis, and by 1H NMR quench when it contains more than one organic component.

Investigation of the correlation between the substituent effect of ligands and the catalytic activity/magnetic properties in fine-tuned rare-earth complexes

Amine-bis(benzothiazole phenol) ligands, C1NNBiBTHP-H2 and CLNNBiBTHP-H2 ligands, were designed for yttrium complexes with analogous structures. A series of nitrophenolate (NP)-type of ligands possessing R substituents with variable electronic properties (R = NO2, Cl, H, CH3) on ortho and/or para position attached to the phenolate rings have been selected as secondary ligands for complexes syntheses. Ten novel yttrium complexes have been synthesized, [Y(C1NNBiBTHP)(NP)(MeOH)] (1–5) and [Y(CLNNBiBTHP)(NP)(MeOH)] (6–10) where the secondary ligand NP = 2,4-dinitrophenol(1 and 6), 2,5-dinitrophenol (2 and 7), 2-nitrophenol (3 and 8), 4-chloro-2-nitrophenol (4 and 9) and 4-methyl-2-nitrophenol (5 and 10), as well as the structures and catalytic properties for lactide (LA) polymerization were both studied. All the core structures and coordination geometries for complexes 1–10 were isostructural. All complexes were demonstrated to be active catalysts for LA polymerization, and the catalytic performance for these complexes was compared. The dysprosium analogues (11, 12 with C1NNBiBTHP-H2 and 13, 14 with CLNNBiBTHP-H2) also been synthesized and the magnetic properties of these compounds are fully studied. Comparing a series of nitrophenolate co-ligands in two different ligand systems, we presented the first example to study the correlation between electronic effect of the ligands and catalytic properties for mononuclear rare-earth complexes.

Anticancer behaviour of 2,2′-(pyridin-2-ylmethylene)bis(5,5-dimethylcyclohexane-1,3-dione)-based palladium(II) complex and its DNA, BSA binding propensity and DFT study

Herein, we report the synthesis and biological evaluation of [Pd(L)(OH2)Cl] complex (where L = 2,2′-(pyridin-2-ylmethylene)bis(5,5-dimethylcyclohexane-1,3-dione) as a novel promising anticancer candidate. The complex was characterized by single-crystal X-ray diffraction and other various spectroscopic techniques. Besides, the optimized structure was determined through DFT calculations revealing that the coordination geometry of [Pd(L)(OH2)Cl] complex is square planar. The binding propensity of [Pd(L)(OH2)Cl] complex with DNA and BSA was assessed by the spectrophotometric method. The antimicrobial profile of the ligand and its [Pd(L)(OH2)Cl] complex was screened against clinically important bacterial strains. [Pd(L)(OH2)Cl] complex showed promising activity against these microorganisms. Pd(L)(OH2)Cl] complex exhibited a potent antiproliferative potential compared to its ligand against different human cancer cells (A549, HCT116, MDA-MB-231, and HepG2) with less toxic effect against normal cells (WI-38). Additionally, [Pd(L)(OH2)Cl] complex exerted its anticancer effects against the most responsive cells (HCT116 cells; IC50 = 11 ± 1 μM) through suppressing their colony-forming capabilities and triggering apoptosis and cell cycle arrest at S phase. Quantitative PCR analysis revealed a remarkable upregulation of the mRNA expression level of p53 and caspase-3 by 4.8- and 5.9-fold, respectively, relative to control. Remarkable binding properties and non-covalent interactions between L and its [Pd(L)(OH2)Cl] complex with the binding sites of different receptors including CDK2, MurE ligase, DNA, and BSA were established using molecular docking. Based on our results, [Pd(L)(OH2)Cl] complex is an intriguing candidate for future investigations as a potential anticancer drug for the treatment of colon cancer.

Heme Spin Distribution in the Substrate-Free and Inhibited Novel CYP116B5hd: A Multifrequency Hyperfine Sublevel Correlation (HYSCORE) Study.

The cytochrome P450 family consists of ubiquitous monooxygenases with the potential to perform a wide variety of catalytic applications. Among the members of this family, CYP116B5hd shows a very prominent resistance to peracid damage, a property that makes it a promising tool for fine chemical synthesis using the peroxide shunt. In this meticulous study, we use hyperfine spectroscopy with a multifrequency approach (X- and Q-band) to characterize in detail the electronic structure of the heme iron of CYP116B5hd in the resting state, which provides structural details about its active site. The hyperfine dipole-dipole interaction between the electron and proton nuclear spins allows for the locating of two different protons from the coordinated water and a beta proton from the cysteine axial ligand of heme iron with respect to the magnetic axes centered on the iron. Additionally, since new anti-cancer therapies target the inhibition of P450s, here we use the CYP116B5hd system-imidazole as a model for studying cytochrome P450 inhibition by an azo compound. The effects of the inhibition of protein by imidazole in the active-site geometry and electron spin distribution are presented. The binding of imidazole to CYP116B5hd results in an imidazole-nitrogen axial coordination and a low-spin heme FeIII. HYSCORE experiments were used to detect the hyperfine interactions. The combined interpretation of the gyromagnetic tensor and the hyperfine and quadrupole tensors of magnetic nuclei coupled to the iron electron spin allowed us to obtain a precise picture of the active-site geometry, including the orientation of the semi-occupied orbitals and magnetic axes, which coincide with the porphyrin N-Fe-N axes. The electronic structure of the iron does not seem to be affected by imidazole binding. Two different possible coordination geometries of the axial imidazole were observed. The angles between gx (coinciding with one of the N-Fe-N axes) and the projection of the imidazole plane on the heme were determined to be -60° and -25° for each of the two possibilities via measurement of the hyperfine structure of the axially coordinated 14N.

Interplay of bipyridine and 4,4′-diaminodiphenylmethane ligands in crystal design of cadmium-based coordination polymers: Structures and unusual photoluminescence quenching

Starting from Cd(ClO4)2·2H2O, four positively charged coordination polymers were prepared and characterized by IR spectroscopic and single-crystal X-ray diffraction methods. The obtained crystalline solids included one-dimensional coordination polymers, {[Cd(dadpm)(2,2′-bpy)2](ClO4)2}n (1), and {[Cd(dadpm)(2,2′-bpy)2](ClO4)2·0.5(H2O)}n (2), and two-dimensional coordination polymers, {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(dadpm)2}n (3), and {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(4,4′-bpy)0.5(dadpm)·EtOH}n (4) (dadpm = 4,4′-diaminodiphenylmethane, 2,2′-bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine). The similar one-dimensional coordination backbones in 1 and 2 were originated from the mononuclear Cd(II) coordination cores with the N6 distorted octahedral geometries going from two terminal bidentate-chelate 2,2′-bpy and two bidentate-bridging dadpm ligands that mediated the successive metal atoms in coordination chains. The charge-balanced perchlorate anions were located in the interchain space complemented by water molecules in 2. The coordination chains were interconnected into H-bonded networks via NH(NH2)⋯O hydrogen bonds. The 2D coordination polymers 3 and 4 comprised the same positively charged square-grid infinite networks {[Cd(4,4′-bpy)2(H2O)2]2+}n with sql topology and with cadmium atom in the N4O2 tetragonally distorted octahedral coordination geometry as a single node. The charge-compensated ClO4− anions and the dadpm molecules were located in the interlayer space in 3 being complemented by the 4,4′-bpy and EtOH molecules in 4. The solid-state photoluminescence in all reported coordination polymers was significantly attenuated and redistributed along the spectrum in comparison with the pure dadpm which revealed the dual emission in the form of a strong narrow signal in the ultraviolet and a weak signal in the yellow regions of spectrum.

Structures, photoluminescence, and magnetism of 1D lanthanide coordination polymers dominated on 3,5‐dichlorobenzoate

AbstractTwo series of novel coordination polymers (CPs), namely, Ln3(3,5‐DCB)9(bipy) (H2O)2·(bipy) [Ln = Nd (1), Sm (2)] and Ln2(3,5‐DCB)6(bipy)H2O [Ln = Eu (3), Gd (4), Tb (5) and Dy (6)], have been synthesized by hydrothermal reaction of a bridging ligand, 3,5‐dichlorobenzoic acid (3,5‐HDCB), with LnCl3·nH2O and N‐donor neutral ligand, 2,2′‐bipyridine (bipy). Single‐crystal x‐ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), and powder x‐ray diffraction (PXRD) for 1–6 are presented. CPs 1 and 2 exhibit trinuclear lanthanide architectures, in which the center Ln(III) are seven‐coordinated and eight‐coordinated adopting monocapped triangular prismatic, distorted square antiprism and bicapped trigonal prismatic coordination geometry, respectively, whereas CPs 3–6 are isostructural dinuclear structures. The center Ln(III) ions are also seven‐coordinated and eight‐coordinated with different coordinate modes adopting distorted monocapped triangular prismatic and square antiprism coordination geometry. Trinuclear CPs 1 and 2 are packed together via hydrogen‐bonding interaction to form the two‐dimensional (2D) supramolecular layers. CPs 3–6 exhibit 2D layers by the π–π interaction. CPs 2, 3, 5, and 6 display the characteristic fluorescent emissions of Sm(III), Eu(III), Tb(III), and Dy(III), respectively. CPs 1 and 4–6 exhibit corresponding weak anti‐ferromagnetic and ferromagnetic interactions of Nd(III), Gd(III), Tb(III), and Dy(III) in the low‐temperature range.

Benchtop Nickel Catalysis Invigorated by Electron-Deficient Diene Ligands.

ConspectusDue to the rarity of precious metals like palladium, nickel catalysis is becoming an increasingly important player in organic synthesis, especially for the formation of bonds with sp3-hybridized carbon centers. Traditionally, catalytic processes involving active Ni(0) species have relied on Ni(COD)2 or in situ reduction of Ni(II) salts. However, Ni(COD)2 is an air- and temperature-sensitive material that requires use in an inert-atmosphere glovebox, and in situ reduction protocols of Ni(II) salts using metallic or organometallic reductants add additional complications to reaction development.This Account chronicles the development of air-stable Ni(0) precursors as replacements for Ni(COD)2 or in situ reduction. Based on Schrauzer's seminal discovery of Ni(COD)(DQ) as an air-stable zerovalent organonickel complex, our research laboratories at Scripps Research and Bristol Myers Squibb have developed a class of precatalysts based on the Ni(COD)(EDD) (EDD = electron-deficient diene) framework, relying on the steric and electronic properties of the supporting diene to render the metal center stable to air, moisture, and even silica gel but reactive to ligand substitution and redox changes.The stable Ni(0) complexes can be accessed through ligand exchange with Ni(COD)2, through reduction of Ni(acac)2 using DIBAL-H, or electrochemically via cathodic reduction of Ni(acac)2 to Ni(COD)2, followed by addition of an EDD ligand in one pot. As a toolkit, the complexes demonstrate reactivity that is equivalent or enhanced compared to Ni(COD)2, catalyzing C-C and C-N cross-couplings, Miyaura borylations, C-H activations, and other transformations. Since the initial report on Ni(COD)(DQ), its reactivity in C(sp2)-CN activation, metallophotoredox, and electric field-induced cross-coupling have also been demonstrated.By incorporating the precatalyst toolkit into reaction discovery campaigns, our laboratories have been able to perform C(sp3)-S(alkyl) couplings and metallonitrenoid carboamination, both of which represent challenging transformations that were inaccessible with traditional phosphine, nitrogen, or electron-deficient olefin ligands. Computational and experimental studies demonstrate how the quinone ligands are hemilabile, adopting η1(O)-bound geometries to relieve steric strain or stabilize transition states and intermediates; redox-active, able to transiently oxidize the metal center; and electron-withdrawing or -donating, depending on metal oxidation state and coordination geometry. These studies show how the ligands enable key steps in catalysis beyond imparting air-stability.Since our report documenting the catalytic activity of Ni(COD)(DQ), many other laboratories have also observed unique reactivity with this precatalyst. Ni(COD)(DQ) was found to offer superior reactivity to Ni(COD)2 in C-N cross coupling to form N,N-diaryl sulfonamides and in preparation of biaryls from aryl halides and benzene through a Ni-mediated, base-assisted homolytic aromatic substitution.

Antioxidant, Cytotoxicity, and Anti-inflammation Activities of Phenanthroline Adducts of Zn(II) and Ni(II) bis(N-alkyl-N-phenyldithiocarbamate)

In this study, 4,7-diphenyl-1,10-phenanthroline adducts of Ni(II) and Zn(II) of N-methyl or ethyl-N-phenyldithiocarbamate were synthesized and the final adducts were represented as [Zn(L1)2L3], [Zn(L2)2L3], [Ni(L1)2L3], [Ni(L2)2L3] (where L1 = methyl, L2 = ethyl, L3 = bathophenanthroline) and characterized using various spectroscopic techniques and elemental analysis. Both the FT-IR and NMR analysis suggest that all the adducts possessed six coordination geometry by the metal atom centres upon the emergence of a new M-N bond. This was shown by the changes observed in the peaks and chemical shifts of the adducts in comparison to the parent complexes. The cytotoxicity, antioxidant, and anti-inflammatory properties were evaluated using different assays to ascertain their biological properties. In all the assays, no noticeable trend was observed between the adducts of similar ligands and metals. Nevertheless, in the antioxidant assays, a good to moderate activity was observed, especially in the DPPH assay, which gave the best radical scavenging properties. Additionally, the estimated IC50 values of 0.011 and 14.76 µM were calculated for the cytotoxicity in the human cervical cancer (HeLa) cell line for both [Zn(L1)2L3] and [Ni(L2)2L3] adducts, respectively, in comparison to 5-Flurouracil (17.48 µM). On the other hand, very low cytotoxicity was found for most of the adducts in the embryonic kidney 293 (HEK 293) cell lines, especially for [Zn(L1)2L3], demonstrating its superior amongst the other adduct and the standard drug. Moreover, the adducts exhibited good to moderate anti-inflammatory properties compared to diclofenac, a controlled drug. These findings thus suggest that the adducts, particularly [Zn(L1)2L3], hold promise as potential anticancer agents and warrant further evaluation through clinical trials.

Surface Structure to Tailor the Electrochemical Behavior of Mixed-Valence Copper Sulfides during Water Electrolysis.

The semiconducting behavior of mixed-valence copper sulfides arises from the pronounced covalency of Cu-S bonds and the exchange coupling between CuI and CuII centers. Although electrocatalytic study with digenite Cu9S5 and covellite CuS has been performed earlier, detailed redox chemistry and its interpretation through lattice structure analysis have never been realized. Herein, nanostructured Cu9S5 and CuS are prepared and used as electrode materials to study their electrochemistry. Powder X-ray diffraction (PXRD) and microscopic studies have found the exposed surface of Cu9S5 to be d(0015) and d(002) for CuS. Tetrahedral (Td) CuII, distorted octahedral (Oh) CuII, and trigonal planar (Tp) CuI sites form the d(0015) surface of Cu9S5, while the (002) surface of CuS consists of only Td CuII. The distribution of CuI and CuII sites in the lattice, predicted by PXRD, can further be validated through core-level Cu 2p X-ray photoelectron spectroscopy (XPS). The difference in the electrochemical response of Cu9S5 and CuS arises predominantly from the different copper sites present in the exposed surfaces and their redox states. In situ Raman spectra recorded during cyclic voltammetric study indicates that Cu9S5 is more electrochemically labile compared to CuS and transforms rapidly to CuO/Cu2O. Contact-angle and BET analyses imply that a high-surface-energy and macroporous Cu9S5 surface favors the electrolyte diffusion, which leads to a pronounced redox response. Post-chronoamperometric (CA) characterizations identify the potential-dependent structural transformation of Cu9S5 and CuS to CuO/Cu2O/Cu(OH)2 electroactive species. The performance of the in situ formed copper-oxides towards electrocatalytic water-splitting is superior compared to the pristine copper sulfides. In this study, the redox chemistry of the Cu9S5/CuS has been correlated to the atomic arrangements and coordination geometry of the surface exposed sites. The structure-activity correlation provides in-depth knowledge of how to interpret the electrochemistry of metal sulfides and their in situ potential-driven surface/bulk transformation pathway to evolve the active phase.

Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T1 relaxivity of Gd-complexes.

High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+ -complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via "click" functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r1 =7.7 mm-1 s-1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.

Structure-Based Identification of Organoruthenium Compounds as Nanomolar Antagonists of Cannabinoid Receptors.

Metal complexes exhibit a diverse range of coordination geometries, representing novel privileged scaffolds with convenient click types of preparation inaccessible for typical carbon-centered organic compounds. Herein, we explored the opportunity to identify biologically active organometallic complexes by reverse docking of a rigid, minimum-size octahedral organoruthenium scaffold against thousands of protein-binding pockets. Interestingly, cannabinoid receptor type 1 (CB1) was identified based on the docking scores and the degree of overlap between the docked organoruthenium scaffold and the hydrophobic scaffold of the cocrystallized ligand. Further structure-based optimization led to the discovery of organoruthenium complexes with nanomolar binding affinities and high selectivity toward CB2. Our work indicates that octahedral organoruthenium scaffolds may be advantageous for targeting the large and hydrophobic binding pockets and that the reverse docking approach may facilitate the discovery of novel privileged scaffolds, such as organometallic complexes, for exploring chemical space in lead discovery.