N2O2 Donor Set Research Articles

Metal Center-Tuned Photocatalytic Carbon Dioxide Reduction for Frameworks with the Tetraphenylethene-Imidazole Ligand.

As heterogeneous photocatalysts that can effectively transform CO2 to CO, two MOFs with different metal centers, namely, [M(tipe)(H2O)2](ClO4)2·solvent (M = Ni named as Ni-MOF and M = Co referred to as Co-MOF), were synthesized by reactions of 1,1,2,2-tetrakis(4-(imidazole-1-yl)phenyl)ethene (tipe) with the corresponding metal perchlorate. Both Ni-MOF and Co-MOF have 3D structures, in which the metal centers have the same coordination environment with the N4O2 donor set. Driven by visible light, the CO production catalyzed by Co-MOF is 6734.1 μmol g-1 with 45.3% selectivity, and in contrast, Ni-MOF has 4601.3 μmol g-1 CO production with 97.6% selectivity in 5 h. Through photoelectrochemical characterization, DFT calculations, and in situ FT-IR measurements, the photocatalytic CO2 reduction process catalyzed by Ni-MOF and Co-MOF was investigated. The results show that the metal center of the MOF is crucial for photocatalytic CO2 reduction. This work offers an innovative approach for controlling the performance of photocatalytic CO2 reduction through tuning the metal centers of architectures.

Two Zn(II) complexes based on bis(benzimidazole) and different dicarboxylate anions: synthesis, structures, and fluorescent properties

Two new zinc(II) complexes, [Zn2(PBM)2(terephthalate)(formate)2] (1) and {[Zn(PBM)(fumarate)]∙H2O}n (2), were synthesized using 1,3-bis(1H-benzo[d]imidazol-2-yl)propane (PBM) and two different dicarboxylic acids under solvothermal conditions. Complexes 1 and 2 have been characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. The structural analysis showed that 1 was a binuclear structure and then formed a 3D supramolecular network structure through hydrogen bond and π-π conjugation, while 2 was a one-dimensional coordination polymer. In 1 and 2, the zinc ions were four-coordinate with an N2O2 donor set and a slightly distorted tetrahedral geometry. The solid-state fluorescence properties indicate that the fluorescence peaks belong to the π*-π transition of the ligand PBM, which has a significant red shift and enhancement with the order being 1 > 2 > PBM. The stronger fluorescence of the complexes than the ligand is due to the immobilization of the ligand through coordination, which reduces the energy loss of thermal vibration. The π∙∙∙π conjugation in 1 results in a stronger fluorescence of 1 than 2. Therefore, coordination and π∙∙∙π conjugation will affect the fluorescence of complexes.

Syntheses, characterizations and crystal structures of two Ni(II) complexes [Ni2(neoc)4(H2O)(CO3)](NO3)2·3H2O and [Ni(bapa)2](NO3)2·H2O and magnetic properties of the carbonato complex

By the reaction of nickel(II) nitrate hexahydrate with 2,9-dimethyl-1,10-phenanthroline (neoc) and bis(3-aminopropyl)amine (bapa) two novel complexes were isolated, namely [Ni2(neoc)4(H2O)(CO3)](NO3)2·3H2O (1) and [Ni(bapa)2](NO3)2·H2O (2). Both structures are ionic and comprise hexacoordinated Ni(II) central atoms. Complex 1 is built up of dinuclear [Ni2(neoc)4(H2O)(CO3)]2+ complex cation, nitrate anions and water solvate molecules. The dinuclear complex cation is centrosymmetric and the two Ni(II) atoms are linked by a μ3-bridging-chelating carbonato ligand which, due to the presence of an inversion centre, exhibits two orientations with equal probability. The coordination sphere of Ni(II) atom is heteroleptic with an N4O2 donor set formed by two chelating neoc ligands and two O-donor atoms from bridging carbonato and aqua ligands. The carbonato ligand was formed by transformation of absorbed carbon dioxide from air (single crystals) or from dry ice (bulk sample). The crystal structure of 2 is formed by [Ni(bapa)2]2+ complex cation, nitrate anions and water solvate molecule. The coordination sphere of Ni(II) atom in 2 is homoleptic with N6 donor set. Both bapa ligands act as double chelating 3 N-donor ligands and are coordinated in mer-fashion. The study of the magnetic response of 1 in the temperature range 1.8–300 K revealed that the system can be considered as a system of antiferromagnetic S = 1 spin dimers with exchange interaction J/hc = -13.86 cm−1 (J/kB = -19.96 K) and axial single-ion anisotropy D/hc = -4.94 cm−1 (D/kB = -7.12 K). The experimental magnetic results were corroborated by ab initio and DFT calculations.

Synergy of experimental and computational chemistry: structure and biological activity of Zn(II) hydrazone complexes.

In this paper, three different Zn(II) complexes with (E)-2-(2-(1-(6-bromopyridin-2-yl)ethylidene)hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride (HLCl) have been synthesized and characterized by single crystal X-ray diffraction, elemental analysis, IR and NMR spectroscopy. All complexes are mononuclear, with the ligand (L) coordinated in a deprotonated formally neutral zwitterionic form via NNO donor set atoms. Complex 1 forms an octahedral geometry with the composition [ZnL2](BF4)2, while complexes 2 [ZnL(NCO)2] and 3 [ZnL(N3)2] form penta-coordinated geometry. Density functional theory (DFT) calculations were performed to enhance our understanding of the structures of the synthesized complexes and the cytotoxic activity of the complexes was tested against five human cancer cell lines (HeLa, A549, MDA-MB-231, K562, LS 174T) and normal human fibroblasts MRC-5. Additionally, antibacterial and antifungal activity of these complexes was tested against a panel of Gram-negative and Gram-positive bacteria, two fungal strains, and a yeast strain. It is noteworthy that all three complexes show selective antifungal activity comparable to that of amphotericin B. Molecular docking analysis predicted that geranylgeranyl pyrophosphate synthase, an enzyme essential for sterol biosynthesis, is the most likely target for inhibition by the tested complexes.

Synthesis, Characterization, and Computational Studies on Gallium(III) and Iron(III) Complexes with a Pentadentate Macrocyclic bis-Phosphinate Chelator and Their Investigation As Molecular Scaffolds for 18F Binding.

With the aim of obtaining improved molecular scaffolds for 18F binding to use in PET imaging, gallium(III) and iron(III) complexes with a macrocyclic bis-phosphinate chelator have been synthesized and their properties, including their fluoride binding ability, investigated. Reaction of Bn-tacn (1-benzyl-1,4,7-triazacyclononane) with paraformaldehyde and PhP(OR)2 (R = Me or Et) in refluxing THF, followed by acid hydrolysis, yields the macrocyclic bis(phosphinic acid) derivative, H2(Bn-NODP) (1-benzyl-4,7-phenylphosphinic acid-1,4,7-triazacyclononane), which is isolated as its protonated form, H2(Bn-NODP)·2HCl·4H2O, at low pH (HClaq), its disodium salt, Na2(Bn-NODP)·5H2O at pH 12 (NaOHaq), or the neutral H2(Bn-NODP) under mildly basic conditions (Et3N). A crystal structure of H2(Bn-NODP)·2HCl·H2O confirmed the ligand's identity. The mononuclear [GaCl(Bn-NODP)] complex was prepared by treatment of either the HCl or sodium salt with Ga(NO3)3·9H2O or GaCl3, while treatment of H2(Bn-NODP)·2HCl·4H2O with FeCl3 in aqueous HCl gives [FeCl(Bn-NODP)]. The addition of 1 mol. equiv of aqueous KF to these chloro complexes readily forms the [MF(Bn-NODP)] analogues. Spectroscopic analysis on these complexes confirms pentadentate coordination of the doubly deprotonated (bis-phosphinate) macrocycle via its N3O2 donor set, with the halide ligand completing a distorted octahedral geometry; this is further confirmed through a crystal structure analysis on [GaF(Bn-NODP)]·4H2O. The complex adopts the geometric isomer in which the phosphinate arms are coordinated unsymmetrically (isomer 1) and with the stereochemistry of the three N atoms of the tacn ring in the RRS configuration, denoted (N)RRS, and the phosphinate groups in the RR stereochemistry, denoted (P)RR, (isomer 1/RR), together with its (N)SSR (P)SS enantiomer. The greater thermodynamic stability of isomer 1/RR over the other possible isomers is also indicated by density functional theory (DFT) calculations. Radiofluorination experiments on the [MCl(Bn-NODP)] complexes in partially aqueous MeCN/NaOAcaq (Ga) or EtOH (Ga or Fe; i.e. without buffer) with 18F- target water at 80 °C/10 min lead to high radiochemical incorporation (radiochemical yields 60-80% at 1 mg/mL, or ∼1.5 μM, concentration of the precursor). While the [Fe18F(n-NODP)] is unstable (loss of 18F-) in both H2O/EtOH and PBS/EtOH (PBS = phosphate buffered saline), the [Ga18F(Bn-NODP)] radioproduct shows excellent stability, RCP = 99% at t = 4 h (RCP = radiochemical purity) when formulated in 90%:10% H2O/EtOH and ca. 95% RCP over 4 h when formulated in 90%:10% PBS/EtOH. This indicates that the new "GaIII(Bn-NODP)" moiety is a considerably superior fluoride binding scaffold than the previously reported [Ga18F(Bn-NODA)] (Bn-NODA = 1-benzyl-4,7-dicarboxylate-1,4,7-triazacyclononane), which undergoes rapid and complete hydrolysis in PBS/EtOH (refer to Chem. Eur. J. 2015, 21, 4688-4694).

Correlating Structure and KA2 Catalytic Activity of ZnII Hydrazone Complexes

AbstractTwo new Zn(II) complexes bearing tridentate hydrazone‐based ligands with NNO or NNS donor atoms were synthesised and characterised by elemental analysis, infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies, and single crystal X‐ray diffraction methods. These complexes, together with four previously synthesised analogues, having hydrazone ligands with a NNO donor set of atoms, were successfully employed as catalysts in the ketone‐amine‐alkyne (KA2) coupling reaction, furnishing tetrasubstituted propargylamines, compounds with unique applications in organic chemistry. DFT calculations at the CAM‐B3LYP/TZP level of theory were performed to elucidate the electronic structure of the investigated Zn(II) complexes, excellently correlating the structure of the complexes to their catalytic reactivity.

First Report on Several NO-Donor Sets and Bidentate Schiff Base and Its Metal Complexes: Characterization and Antimicrobial Investigation

The condensation product of the reaction between aniline and salicylaldehyde was a 2-(2-hydroxybenzylidinemine)—aniline Schiff base bidentate ligand (L). L was used to generate complexes by interacting with the metal ions lanthanum(III), zirconium(IV), yttrium(III), and copper(II), in addition to cobalt(II). Various physicochemical techniques were utilized to analyze the synthesized L and its metal chelates, including elemental analysis (CHN), conductimetry (Λ), magnetic susceptibility investigations (μeff), Fourier-transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR) spectroscopy, ultraviolet–visible (UV-Vis.) spectrophotometry, and thermal studies (TG/DTG). FT-IR revealed that the L molecule acted as a bidentate ligand by binding to metal ions via both the oxygen atom of the phenolic group in addition to the nitrogen atom of the azomethine group. Additionally, 1H NMR data indicated the formation of complexes via the oxygen atom of the phenolic group. An octahedral geometrical structure for all of the chelates was proposed according to the UV-Vis. spectra and magnetic moment investigations. Thermal analysis provided insight into the pattern of L in addition to its chelates’ breakdown. In addition, the investigation furnished details on the chelates’ potential chemical formulas, the characteristics of adsorbed or lattice H2O molecules, and the water that is coordinated but separated from the structure at temperatures exceeding 120 °C. The thermodynamic parameters utilizing Coats–Redfern in addition to Horowitz–Metzger equations were studied. The antimicrobial effectiveness of L and its chelates against distinct species of bacteria and fungi was studied using the disc diffusion method. Cu(II) and Y(III) chelates had significant antimicrobial activity against Staphylococcus aureus and Micrococcus luteus.

Engineered organotin(IV) and vanadium(V) derivatives with distinct coordination modes and luminescent properties for the efficient detection and quantification of permanganate ions.

The distinction in coordination modes of metal complexes leads to their versatile structural features and unique properties. Here, we report two tetradentate Schiff base ligands (H2L1 and H2L2) bearing N2O2 donor sets, tactically selected to provide distinct coordination modes with different metal ions. The ligands were utilized to synthesize their organotin(IV) (1-4) and vanadium(V) (5) derivatives. The synthesized compounds were characterized using elemental analysis, FT-IR spectroscopy, multi-nuclei NMR (1H, 13C, and 119Sn) spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The organotin(IV) derivatives (1-4) displayed hepta-coordination around both the Sn centres as they were achieved in their dimeric form. Contrariwise, the vanadium(V) compound (5) was isolated as a mononuclear entity exhibiting penta-coordinated geometry around the vanadium centre. The variation in the coordination modes was evident in their UV-vis and fluorescence spectra. The organotin(IV) compounds (1-4) exhibited a strong emission band centred at 468nm when excited at a wavelength of 360nm whereas the vanadium(V) (5) derivative displayed poor fluorogenic response. Compound 1 was further explored for the fluorogenic chemo-sensing of permanganate ions (MnO4-) amongst various anions by quenching response. A detailed investigation of the recognition of permanganate ions was accomplished by spectrofluorometric, spectroscopic (119Sn NMR), mass spectrometric, and computational studies.

The copper(II) coordination chemistry of alkyl substituted bispyrazole pyridine ligands: Structure and spectral properties

Tridentate, planar nitrogen containing ligands based on pyridine and pyrazoles were synthesized by the reaction of 2,6-dibromopyridine with the sodium salts of 3,5-dimethylpyrazole and 3,5-diisopropylpyrazole to yield 2,6-bis(3,5-dimethyl-N-pyrazolyl)pyridine (L0py) and 2,6-bis(3,5-diisopropyl-N-pyrazolyl)pyridine (L1py), respectively. The conformation of the pyrazole rings in the solid-state structures of both L0py and L1py were anti due to relatively low repulsion between the alkyl substituents. Both copper(II) chlorido complexes [CuCl2(L0py)] and [CuCl2(L1py)] were five-coordinate with solid-state structures best described as distorted square-pyramidal geometry involving N3Cl2 donor sets. The ν(Cu–Cl) energies and Cu–Cl bond lengths were clearly different due to the different donating properties of the two ligands. By comparison, the structure of copper(II) trifluoromethanesulfonato complex [Cu(OTf)2(H2O)(L1py)] was six-coordinate with highly distorted octahedral geometry involving an N3O3 donor set. The solution UV–Vis spectra of [CuCl2(L0py)], [CuCl2(L1py)], and [Cu(OTf)2(H2O)(L1py)] revealed π-π* transition bands red-shifted by ∼30 nm on complexation. The d-d transition bands of all three copper(II) complexes were observed at almost the same energy of ∼750 nm, while the corresponding solid-state UV–Vis spectra exhibited absorptions at ∼1010 nm and 674 nm due to differences in coordination geometry. These structural changes in the solution-state were supported by results from EPR spectroscopy.

Static and Dynamic Magnetic Properties of a Co(II)‐Complex with N2O2Donor Set – A Theoretical and Experimental Study

AbstractA representative Co(II) based single ion magnet (SIM) with N2O2donor set and distorted pseudo‐tetrahedral geometry has been synthesized and characterized to study the atomic and electronic structure. DC magnetometry results have been evaluated by means of a phenomenological Hamiltonian approach regarding zero field splitting (ZFS) parameters and compared with results from ab‐initio multi‐reference CASSCF (complete active space self‐consistent field) calculations and qualitative ligand field theory (AILFT). Profound investigation of spin‐lattice relaxation with the variation of temperature (from 1.8 to about 8 K) and magnetic field (at 14 different fields from zero up to 1 T) have been performed based on AC magnetometry. Under an applied dc magnetic field, spin‐lattice relaxation occurs via a direct process withT2temperature dependence due to limited heat transfer at very low temperature and above 5 K relaxation by an Orbach process with an energy barrier of≈80 K dominates.

Dinuclear Phenoxo-Bridged Nickel(II) and Copper(II) Complexes of Phenolate-Based Tripodal Ligand: Theoretical and Experimental Insights

Three dinuclear complexes of composition [NiII 2(L)2][ClO4]2 and [CuII 2(L)2(OClO3)2] . 3H2O have been synthesized using a new tripodal ligand [(2-pyridyl)methyl](2-benzyl)-aminomethyl}-phenol (HL)], in its deprotonated form, providing a N2O donor set. Crystallographic analyses reveal that [CuII 2(L)2(OClO3)2] . 3H2O has a diphenoxo-bridged structure. In [CuII 2(L)2(OClO3)2] . 3H2O, each metal center is MIIN2O3-coordinated with a square-pyramidal environment for each copper(II) center. In this work, the molecular structure, harmonic vibrational frequencies and UV-Vis of [NiII 2(L)2]2+ and [CuII 2(L)2]2+ has been explored. With the help of density functional theory (DFT)/B3LYP techniques and LANL2DZ as a basis set, the ground-state molecule shape and vibrational frequencies were computed. The basic vibrations were allocated using the VEDA program to compute the potential energy distribution (PED) of the vibrational modes. The band gap energies of the title complexes ([NiII 2(L)2]2+ and [CuII 2(L)2]2+) are 3.21 eV and 1.59 eV, respectively, according to HOMO-LUMO energies. The maximal absorption wavelength and band gap energy of the title complexes were calculated theoretically using the UV absorption spectra. MEP analysis identifies electrophilic and nucleophilic sites. Hirshfeld surface analysis was used to characterize the 3D intermolecular interactions in ([NiII 2(L)2]2+ and [CuII 2(L)2]2+) of the crystal surface, whereas fingerprint plots were used to explain the 2D interactions. The biological activity of the complexes was investigated using molecular docking.

Synthesis, crystal structures and fluorescence properties of two 1D Zn(II) homologous coordination polymers

Abstract A pair of zinc(II)-based one-dimensional (1D) homologous coordination polymers, [Zn(Hdba)2(bib)] n (1) and [Zn(Hdba)2(bmib)] n (2), where H2dba = 3-hydroxybenzoic acid, bib = 1,4-bis(1-imidazolyl)benzene, and bmib = 1,4-bis(2-methyl-1H-imidazol-1-yl)benzene were hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. The results revealed that 1 and 2 have the same zigzag infinite chain framework through the partially deprotonated Hdba– monodentate linkage and with μ 2-bib bridging the Zn(II) atoms in 1, and with μ 2-bmib bridges for the Zn(II) atoms in 2. For both 1 and 2, each zinc atom has a slightly twisted tetrahedral configuration with a N2O2 donor set. These chains of 1 and 2 are further connected into three-dimensional (3D) supramolecular structures through O–H···O, C–H···O hydrogen bonds and π···π, C–H···π stacking interactions for 1, and O–H···O, C–H···O hydrogen bonds for 2. Topologically, the 3D hydrogen-bonded organic framework or the 2D π-stacking structure of 1 can be simplified as a 4-connected dia Diamond type with a Schläfli symbol {66}, or as a 4-connected sql type with a Schläfli symbol {44·62} and a Shubnikov tetragonal plane net. The thermal stability and the solid-state fluorescence properties of 1 and 2 were investigated.

Kink distortion of the pseudo-S4 axis in pseudotetrahedral [N2O2] bis-chelate cobalt(II) single-ion magnets leads to increased magnetic anisotropy.

Two new mononuclear cobalt(II) complexes with the general formula [Co(L1,2)2] (1 and 2) were synthesized using bidentate Schiff base ligands with NO donor set, namely, 2-(benzothiazole-2-ylimino)methyl-5-(diethylamino)phenol (HL1) and its methyl substituted derivative 2-(6-methylbenzothiazole-2-ylimino)methyl-5-(diethylamino)phenol (HL2). X-ray structure analysis reveals a distorted pseudotetrahedral coordination sphere at the cobalt(II) ion, that cannot be described by a simple twisting of the two ligand chelate planes with respect to each other, which would imply a rotation about the pseudo-S4 axis of the complex. Such a pseudo-rotation axis would approximately be colinear with the two vectors defined by the cobalt ion and the two centroids of the chelate ligands, where the angle κ between the two vectors would be 180° in an ideal pseudotetrahedral arrangement. For complexes 1 and 2, the observed distortion can be characterized by a significant bending at the cobalt ion with angles κ of 163.2° and 167.4°, respectively. Magnetic susceptibility and FD-FT THz-EPR measurements together with ab initio calculations reveal an easy-axis type of anisotropy for both complexes 1 and 2, with a spin-reversal barrier of 58.9 and 60.5 cm-1, respectively. For both compounds, frequency-dependent ac susceptibility measurements show an out-of-phase susceptibility under applied static fields of 40 and 100 mT, which can be analyzed in terms of Orbach and Raman processes within the observed temperature range.

Binuclear Nickel Complexes of a New Di(hydroxyphenyl)imidazolate

Here, we report a new di(hydroxyphenyl)imidazolate ligand with an N2O2 donor set synthesized by a modified Debus–Radziszewski procedure. Its binuclear nickel(II) complexes feature a weak antiferromagnetic interaction with J12 = −3.16 cm−1 between the two nickel(II) ions identified by magnetometry measurements. As follows from cyclic voltammetry experiments and DFT calculations, they undergo ligand-centered oxidation via the formation of cation radicals with short lifetimes that can be potentially stabilized by bulkier t-butyl groups in the ortho-positions of the ligand. The reported ligand widens the range of the building blocks available to molecular magnetism community and thus provides new ways to the design of magnetic materials with switchable properties.

Opposing magnetic communications in two dinuclear Ni(II) complexes: Ferromagnetic Ni-N-Ni and antiferromagnetic Ni-O-Ni moiety

Two dinuclear Ni(II) complexes [Ni2(L)2(N3)2(H2O)]·2H2O (1) and [Ni2(L)2(NCS)2(H2O)] (2) [HL = 2-methoxy-6-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol] have been synthesized and characterized by single crystal X-ray crystallography and FT-IR spectroscopy. The complexes 1 and 2 are dinuclear and structurally close comparable with metals doubly bridged by a pseudohalide anion (μ1,1-azido and N,N-thiocyanato, respectively) and a μ-(phenoxido). The two HL ligands behave differently with N2O2 and N2O donor set towards the octahedral metal centres. Magnetic studies indicate an overall ferromagnetic interaction between nickel(II) centers in both the complexes. The experimental data can be simulated using the isotropic exchange Hamilton operator Ĥ = −2JS1S2 with following parameters J = +7.9(4) cm−1, g1,2 = 2.246(5), D1,2 = 2.35(10) cm−1 for complex 1 and J = +13.3(5) cm−1, g1,2 = 2.102(4), D1,2 = 4.18(12) cm−1, for complex 2. The structures of the complexes were theoretically optimized in their ground state and the experimental UV–vis electronic absorption spectral data have been compared with the theoretical results obtained from TD-DFT calculation.

Synthesis and Crystal Structures of Mn(II) and Co(II) Complexes as Catalysts for Oxidation of Cyclohexanone

The global demand on adipic usage in the production of plasticizers and synthetic polyamide is increasing. In line with the search for an efficient and energy-conserving way to isolate adipic acid (AA) in good yields, this paper introduces the oxidization of cyclohexanone utilizing two new coordination compounds, [Mn(2,6-pydc)2](imi) (1) and [Co(H2pza)2(H2O)2(NO3)].NO3 (2), as catalysts. Compounds 1 and 2 were synthesized by room temperature and refluxing methods, and characterized by spectral analyses (IR and UV-Vis.), SEM, BET, TGA, elemental, and X-ray crystallography. The single crystal structure of compound 1 revealed that pyridinedicarboxylate (2,6-pydc) and imidazole (imi) moieties were coordinated to the Mn(II) atom through imine nitrogen and deprotonated oxygen atoms, to form an undistorted octahedral coordination geometry with the N2O4 donor set. The axial and equatorial planes containing O2, O4, O5, and O7 atoms were from two adjacent 2,6-pydc ligands which formed the unidendate donor ligand; imi, on the other hand, acted as a bidendate donor ligand. For compound 2, the Co(II) atom was being coordinated by two pyrazinamide (H2pza) moieties, which acted as an unidendate donor ligand; two water molecules occupying the axial position, and one nitrate molecule occupying the apical position, were within the coordination sphere; a nitrate molecule was disordered outside the coordination sphere. The distance, 4.658 Å, between the Co1 atom and the N8 atom of the uncoordinated nitrate molecule, was within the range reported elsewhere. Cyclohexanone peroxidation experiments revealed that compound 1 exhibited unique catalytic performance by giving a 72.8% yield in adipic acid, in comparison to the 71.3% yield obtained with compound 2. The yields in AA were maintained by way of recyclability evaluation. The reaction kinetics of compound 2 gave less activation energy, Ea 2938 J mol−1, while the thermodynamic parameters indicated that the chemical reactivity of cyclohexanone on the active surfaces of compounds 1 and 2 was via monolayer physisorption.

The X-ray crystal structures, molecular docking and biological activities of two novel Cu(II) and Zn(II) complexes with a ligand having a potentially N4O2 donor set and two nitro phenyl rings as pendant arms

A new ligand (L) containing two nitro phenyl rings as side chains was synthesized. The reaction of this ligand with copper(II) and zinc(II) metal ions gave complexes with different coordination environments. The free ligand and the metal complexes were characterized using a number of spectroscopic methods. The crystal structure of [ZnLBr]ClO4 showed that the Zn(II) ion was in a distorted square pyramidal environment. The crystal structure of [CuL](ClO4)2 showed that the Cu(II) ion is in a tetragonally distorted octahedral environment. Molecular docking studies with DNA indicated that the binding of L, [ZnLBr]ClO4 and [CuL](ClO4)2 involved the major groove of DNA, H-bonds and Vander Waals interactions. In contrast, the molecular docking of L, [ZnLBr]ClO4 and [CuL](ClO4)2 with human glutathione reductase (GR) showed that the dominant interactions of these compounds with GR were H-bonding, vander Waals and hydrophobic interactions. The antioxidant activity of the synthesized complexes was analyzed by the free radical scavenging activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay with [CuL](ClO4)2 showing maximum activity. In addition, in vitro anticancer activity of the complexes against human breast MCF-7 cancer cell line was confirmed through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay. All compounds showed a dose-dependent inhibitory effect on the growth of breast cancer cells with the inhibition activity of [CuL](ClO4)2 being more active than the other synthesized compounds. Furthermore, results from the antibacterial activity screening of the compounds against two Gram-positive and Gram-negative pathogenic bacteria by the micro-broth dilution and disk diffusion methods indicated that [CuL](ClO4)2 complex had the strongest antibacterial potential.

{N'-[(E)-1-(5-Chloro-2-oxidophen-yl)ethyl-idene]-4-meth-oxy-benzohydrazidato-κ3 O,N',O'}(1H-imidazole-κN 3)nickel(II).

In the title complex, [Ni(C16H13ClN2O3)(C3H4N2)], the NiII ion is coordinated by two O atoms and one N atom derived from the dianionic N'-[(1E)-1-(5-chloro-2-hy-droxy-phen-yl)ethyl-idene]-4-meth-oxy-benzohydrazide ligand and one N atom from the imidazole mol-ecule. The N2O2 donor set defines an approximate square-planar geometry. The dihedral angles between the imidazole ring and the fused six-membered and meth-oxy-benzene rings are 17.78 (14) and 13.23 (16)°, respectively; the dihedral angle between the C6 rings is 6.63 (12)°. The most prominent feature of the mol-ecular packing is the formation of 41-helical chains (along the c axis) mediated by imidazole-N-H⋯O(phenoxide) hydrogen bonding; these are linked by methyl-C-H⋯Cl inter-actions.

Synthesis and structures of three benzoannelated macrobicyclic diamides.

We report the synthesis and structures of 9,10,20,21-tetrahydro-5,14-(ethanooxyethano)dibenzo[e,q][1,4,10,13,7,16]tetraoxadiazacyclooctadecine-6,13-dione [systematic name: 8,11,21,24,29-pentaoxa-1,18-diazatetracyclo[16.8.5.02,7.012,17]hentriaconta-2,4,6,12(17),13,15-hexaene-19,26-dione C24H28N2O8, I], 6,7,9,10,12,13,20,21-octahydro-5,14-(ethanooxyethano)dibenzo[e,q][1,4,10,13,7,16]tetraoxadiazacyclooctadecine-23,27-dione (8,11,21,24,29-pentaoxa-1,18-diazatetracyclo[16.8.5.02,7.012,17]hentriaconta-2,4,6,12,14,16-hexaene-27,31-dione; C24H28N2O7, II), and 9,10,20,21-tetrahydro-5,14-(ethanooxyethanooxyethano)dibenzo[e,q][1,4,10,13,7,16]tetraoxadiazacyclooctadecine-6,13-dione [8,11,21,24,29,32-hexaoxa-1,18-diazatetracyclo[16.8.8.02,7.012,17]tetratriaconta-2,4,6,12(17),13,15-hexaene-19,26-dione; C26H32N2O7, III]. All three compounds are made up of two tertiary diamides and are composed of two 15-membered rings with N2O3 donor sets and one 18-membered ring with an N2O4 donor set (compounds I and II) or three 18-membered rings with N2O4 donor sets (compound III). The solid-state structures of compounds I and II show little effects from the movement of the amide groups. However, compound III has a larger cavity and a different orientation of donor atoms in comparison to compounds I and II.

Electrocatalytic Water Oxidation Activity of Molecular Copper Complexes: Effect of Redox-Active Ligands.

Two molecular copper(II) complexes, (NMe4)2[CuII(L1)] (1) and (NMe4)2[CuII(L2)] (2), ligated by a N2O2 donor set of ligands [L1 = N,N'-(1,2-phenylene)bis(2-hydroxy-2-methylpropanamide), and L2 = N,N'-(4,5-dimethyl-1,2-phenylene)bis(2-hydroxy-2-methylpropanamide)] have been synthesized and thoroughly characterized. An electrochemical study of 1 in a carbonate buffer at pH 9.2 revealed a reversible copper-centered redox couple at 0.51 V, followed by two ligand-based oxidation events at 1.02 and 1.25 V, and catalytic water oxidation at an onset potential of 1.28 V (overpotential of 580 mV). The electron-rich nature of the ligand likely supports access to high-valent copper species on the CV time scale. The results of the theoretical electronic structure investigation were quite consistent with the observed stepwise ligand-centered oxidation process. A constant potential electrolysis experiment with 1 reveals a catalytic current density of >2.4 mA cm-2 for 3 h. A one-electron-oxidized species of 1, (NMe4)[CuIII(L1)] (3), was isolated and characterized. Complex 2, on the contrary, revealed copper and ligand oxidation peaks at 0.505, 0.90, and 1.06 V, followed by an onset water oxidation (WO) at 1.26 V (overpotential of 560 mV). The findings show that the ligand-based oxidation reactions strongly depend upon the ligand's electronic substitution; however, such effects on the copper-centered redox couple and catalytic WO are minimal. The energetically favorable mechanism has been established through the theoretical calculation of stepwise reaction energies, which nicely explains the experimentally observed electron transfer events. Furthermore, as revealed by the theoretical calculations, the O-O bond formation process occurs through a water nucleophilic attack mechanism with an easily accessible reaction barrier. This study demonstrates the importance of redox-active ligands in the development of molecular late-transition-metal electrocatalysts for WO reactions.