In The Nickel Research Articles

Synthesis, Crystal Structure Determination and Magnetic Study of a New [2 × 2] Grid Tetranuclear Fe(II) and Ni(II) Complexes Derived from the Ligand 1, 5-Bis(1-(Pyridin-2-Yl) Ethylidene) Carbonohydrazide)

Complexes of nickel (II) and iron (III) are easily synthetized using the symmetrical ligand 1,5-bis(1-(pyridin-2-yl)ethylidene)carbonohydrazide) (H2L) and metal nitrate salts. Square [2x2] grids structure of one tetranuclear iron and one tetranuclear nickel complex were isolated. X ray diffraction analysis reveals that the crystal structures of the two complexes are similar. The asymmetric unit of each complex consists of four cationic ligand molecules and four metal ions. Each ligand acts in its monodeprotonated form through five coordination sites such as two pyridine nitrogen atoms, two azomethine nitrogen atoms and one oxygen atom. Each of the four ligand molecules acts as a bridge between two metal ions yielding a square 2 x 2 grid structure. Each of the metal ion is hexacoordinated and is situated in a N4O2 core and the environment is best described as a severely distorted square bipyramidal geometry. Electrochemical studies show two electrons process for complex 1 and one electron process for complex 2. Variable temperature magnetic study shows that antiferromagnetic coupling is stronger in the nickel(II) than in the iron(II) complex. Perfect correlation between the magnetic properties and the crystallographic data are observed in both complexes.

Phase equilibria, structural and thermodynamic properties of phases in the nickel (II) methanesulfonate – Water, cobalt (II) methanesulfonate – Water and manganese (II) methanesulfonate – Water systems

Solid-liquid equilibria in the Ni(CH3SO3)2-H2O, Co(CH3SO3)2-H2O, and Mn(CH3SO3)2-H2O systems were studied by isothermal solubility and DSC methods. TG and X-Ray diffraction were used to identify solid phases in equilibria with the solution. Water vapor pressure was determined by static method at 288.15 К, 298.15, and 308.15 K in the Ni(CH3SO3)2-H2O, Co(CH3SO3)2-H2O and Mn(CH3SO3)2-H2O systems. Based on vapor–liquid (VLE) and solid–liquid (SLE) equilibria data, parameters of the Pitzer-Simonson-Clegg model were obtained. Stability parameters of the hydrates Ni(CH3SO3)2·12H2O, Ni(CH3SO3)2·6H2O, Co(CH3SO3)2·4H2O, Co(CH3SO3)2·9H2O, Co(CH3SO3)2·6H2O, Mn(CH3SO3)2·12H2O, and Mn(CH3SO3)2·2H2O were estimated. Binary phase diagram fragments were calculated.

Machine‐Learning Classification for the Prediction of Catalytic Activity of Organic Photosensitizers in the Nickel(II)‐Salt‐Induced Synthesis of Phenols

AbstractCatalytic systems using a small amount of organic photosensitizer for the activation of an inorganic (on‐demand ligand‐free) nickel(II) salt represent a cost‐effective method for cross‐coupling reactions, while C(sp2)−O bond formation remains less developed. Herein, we report a strategy for the synthesis of phenols with a nickel(II) salt and an organic photosensitizer, which was identified via an investigation into the catalytic activity of 60 organic photosensitizers consisting of various electron donor and acceptor moieties. To examine the effect of multiple intractable parameters on the catalytic activity of photosensitizers, machine‐learning (ML) models were developed, wherein we embedded descriptors representing their physical and structural properties, which were obtained from DFT calculations and RDKit, respectively. The study clarified that integrating both DFT‐ and RDKit‐derived descriptors in ML models balances higher “precision” and “recall” across a wide range of search space relative to using only one of the two descriptor sets.

Machine-Learning Classification for the Prediction of Catalytic Activity of Organic Photosensitizers in the Nickel(II)-Salt-Induced Synthesis of Phenols.

Catalytic systems using a small amount of organic photosensitizer for the activation of an inorganic (on-demand ligand-free) nickel(II) salt represent a cost-effective method for cross-coupling reactions, while C(sp2 )-O bond formation remains less developed. Herein, we report a strategy for the synthesis of phenols with a nickel(II) salt and an organic photosensitizer, which was identified via an investigation into the catalytic activity of 60 organic photosensitizers consisting of various electron donor and acceptor moieties. To examine the effect of multiple intractable parameters on the catalytic activity of photosensitizers, machine-learning (ML) models were developed, wherein we embedded descriptors representing their physical and structural properties, which were obtained from DFT calculations and RDKit, respectively. The study clarified that integrating both DFT- and RDKit-derived descriptors in ML models balances higher "precision" and "recall" across a wide range of search space relative to using only one of the two descriptor sets.

Use of Chiraphos as a Highly Efficient Ligand in the Nickel(II)-catalyzed Cross-coupling Polymerization for the synthesis of Poly(1,4-arylene)s

Chiraphos (2,3-diphenylphosphinobutane) serves as a highly effective ligand for nickel catalysts in cross-coupling polymerization reactions. Nickel(II) catalyst efficiently promotes the cross-coupling polymerization of 2,5-differently substituted 1,4-dihalobenzene particularly bearing a sterically congested substituent at the side chain affording the corresponding poly(1,4-phenylene). Such a highly active catalyst allowed the polymerization with a diverse degree of polymerization with controlled molecular weight.

Crystal Structures and Magnetic Properties of Diaquatetrapyridinenickel(II) and Diaquatetrapyridinecobalt(II) Complexes

Metal complexes with pyridine ligands (py) have not been crystallographically characterized in large numbers, while a large number of 2,2′-bipyridine (bpy) complexes have been structurally characterized. Against this background of scarcity of py complexes, the aim of this study was to characterize the structures and magnetic properties of complexes with pyridine ligands. In this study, new py complexes, trans-[Ni(H2O)2(py)4][BPh4]2·4py (1) and trans-[Co(H2O)2(py)4][BPh4]2·4py (2), were prepared and characterized by the single-crystal X-ray diffraction method and magnetic measurements. In the crystal structure analysis, both complexes were found to have octahedral trans-N2O4 coordination geometry, and the coordination of the trans-aqua ligands was found to be enhanced by the hydrogen-bonded pyridine molecules as a base. In the simultaneous analysis of magnetic susceptibility and magnetization, both complexes were found to show strong magnetism in one direction (χz > χx, χy; Mz > Mx, My), and this was explained by the enhancement of the axial aqua ligands. In the nickel(II) complex, the strong axial ligand field was found to cause negative zero-field splitting (D < 0) to show the magnetic behavior, while in the cobalt(II) complex, the strong axial π-orbital effect was found to cause negative ligand field splitting (Δ) in the 4T1 ground state to show the magnetic behavior.

Expanding the Boxmi Ligand Family: Synthesis and Application of NON and NSN Ligands.

Two synthetic strategies for a new family of neutral NON ligands featuring a "bis(oxazolinylmethylidene)isobenzofuran" framework (boxman) are reported. A Pd-mediated cyclization reaction forming the isobenzofuran core constitutes the key reaction in the eight-step synthetic route to the nonbackbone-methylated target compound H,Rboxman. In contrast, the introduction of two additional methyl groups provides stereochemical control during backbone construction and thereby access to the methylated derivative Me,Rboxman, which was synthesized in five steps and improved yields. In addition, the synthetic sequence was transferred to the thio analogue, providing access to the NSN ligand H,Rboxmene. Subsequent complexation experiments with iron and cobalt chloride precursors afforded the four-coordinated chlorido complexes Me,RboxmanMCl2 (R = Ph, iPr; M = Fe, Co) and established the boxman family as trans-chelating, bidentate bis(oxazoline) ligands. Application of the latter in the nickel(II)- and zinc(II)-catalyzed α-fluorination of β-ketoesters and oxindoles (up to 98% yield and 94% ee) demonstrated their suitability for enantioselective catalysis.

Synthesis, X-ray Structural Characterization, and DFT Calculations of Mononuclear Nickel(II) Complexes Containing Diamine and Methacrylate Ligands.

The mononuclear Ni(II) complexes [Ni(en)2(H2O)2](MAA)2 (1) and [Ni(pn)2(MAA)2] (2), where MAA, en and pn are methacrylate, ethylendiamine and 1,3-propylendiamine, respectively, have been synthesized and characterized by elemental analysis, FT-IR and UV�Vis spectroskopy. Structures of the complexes have been determined by single-crystal X-ray diffraction analyses. In the nickel(II) complexes 1 and 2 nickel(II) ion is six-coordinate and has a distorted octahedral geometry. Ni(II) is bonded to four nitrogen atoms of the two diamines and additionally to two oxygen atoms of aqua ligand in 1, and two oxygen atoms of methacrylate ligands in 2. The theoretical geometries of the studied compounds have been calculated by means of density functional theory (DFT) at the B3LYP/6-311+G(d,p)/LanL2DZ level and considering effective core potential (ECP). The comparison of the results indicates that the employed DFT method yields good agreement with experimental data.

Stability, lability, spectral parameters and structure of complexes and stereoselective effects in the nickel(II) – l/d/dl-histidine – l/d/dl-methionine systems

Abstract The equilibrium constants, spectral characteristics of complexes, formation thermodynamic parameters and constants of the chemical exchange reactions in the nickel(II) – l / d / dl -histidine (HisH) – l / d / dl -methionine (MetH) systems (25 °C, 1.0 mol dm−3 KNO3) over wide ranges of pH and ligands to metal ratio were calculated from the pH-potentiometry, multi-wavelength electronic spectroscopy, calorimetry and NMR relaxation data. Based on the DFT computation the structures of some complexes have been proposed. Significant enantioselective effects are exhibited in the formation constants and in some electronic spectra and NMR relaxation parameters of a number of complexes with the meso-forms domination. For the Ni(His)2 complex the process of alkaline catalysis of proton exchange with the short-time N-H proton removal from the coordinated imidazole fragment was characterized. It was shown that in the ligand exchange reaction between Ni(His)2 and His− the Ni(His)3− complex participates as an intermediate. It was found that the Met− thiomethyl group is not bounded in the Ni(Met)+ and Ni(Met)2 complexes but coordinated in the Ni(His)(Met) form. Main factors determining stereoselectivity in the complex formation processes and ligand exchange reactions in the systems studied were identified as trans effect, solvation effect and a new type of interligand thiomethyl group–imidazole ring weak interaction.

Effect of the Structure of Pyridine Ligands and the Substituent in the Carboxylate Anion on the Geometry of Transition Metal Complexes [M2(O2CR)4L2

A series of binuclear tetracarboxylate-linked Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) complexes with 1,2-substituted pyridine, viz., 2,3-cyclododecenopyridine (L), were prepared. Study of the crystal structures of isolated compounds (CIF file CCDC nos. 1575855–1575859) revealed a distortion of the {Ni2(O2CR)4L2} binuclear moiety, manifested as a change in the NiNiN angle (151.67°), in the bridging function of two out of the four carboxylate groups (from μ2- to (κ2,μ2-)), and in the coordination environment of the metal ion (NiO5N). The results were analyzed in comparison with known data. The magnetic properties of copper(II) and nickel(II) complexes were studied. The copper(II) complex is diamagnetic as a result of strong exchange interactions between the unpaired electrons; in the nickel(II) complex antiferromagnetic exchange interactions were detected (JNi–Ni =–25 cm–1).

Copper(II), nickel(II), and zinc(II) complexes with o-tozylaminobenzaldehyde 4,6-dimethylpyrimidyl hydrazone

o-Tosylaminobenzaldehyde dimethylpyrimidyl hydrazone and its copper(II), nickel(II), and zinc(II) complexesare synthesized and studied. According to the X-ray diffraction data, the zinc(II) complex has the structure of a tetragonal pyramid with the N3O donor ligand environment. According to EPR and magnetochemistry data, the copper(II) complex has a similar structure of the chelate core. In the nickel(II) complex, the solvent molecule completes the coordination core to an octahedron.

Thermodynamic parameters of complexation reactions between nickel(II) ion and L-serine in aqueous solutions

A thermochemical study of coordination equilibria in the nickel(II) ions-L-serine system was carried out. The heats of reaction between solutions of an amino acid and nickel(II) nitrate at 288.15, 298.15, and 308.15 K and ionic strength of 0.25, 0.50, and 0.75 (KNO3) were measured. The heats of dilution of nickel nitrate solution in background electrolyte solutions were determined under identical conditions to make proper corrections. The results were processed with allowance for stepwise equilibria. The standard thermodynamic parameters of the complexation processes were calculated. The effect of temperature on heats of complexation reactions in the L-serine-nickel(II) ions was studied. The standard enthalpies of formation of NiSer+, NiSer2, and NiSer3− complexes in aqueous solutions were determined.

Monometallic nickel(II) complexes containing N,N′-iminopyridine chelating ligands with dendritic substituents: The influence of dendrimer topology on the catalytic oligomerization and polymerization of ethylene

Iminopyridine ligands of general formula Gn-PBE-ONN (Gn-PBE=Fréchet-type dendritic wedges of generation G0 (1), G1 (2), G2 (3), and G3 (4); –ONN=-O-4-(2,5-Me2C6H2)-NCH-2-py) have been prepared starting from H-ONN. Reaction of these bidentate ligands with [NiBr2(DME)] results in the nickel(II) complexes [NiBr2(Gn-PBE-ONN)] (5–8). The methylaluminoxane (MAO)-activated monometallic complexes have been studied in the transformation of ethylene into mixtures of polyethylene and oily oligomers, and their catalytic performance scrutinized as a function of dendritic size. A comparison with the behavior observed for related polymetallic dendrimers has enabled the dendritic features that affect various catalytic parameters to be determined. Thus, it has been possible to discern whether the dendritic effect detected in the catalysis should be ascribed to the metallic nuclearity rather than the bulkiness of the metallodendrimer.

The Synthesis of a New Class of Chiral Pincer Ligands and Their Applications in Enantioselective Catalytic Fluorinations and the Nozaki–Hiyama–Kishi Reaction

A new class of chiral tridentate N-donor pincer ligands, bis(oxazolinylmethylidene)isoindolines (boxmi), was synthesized in three steps starting from readily available phthalimides. Their reaction with ethyl (triphenylphosphoranylidene)acetate by means of a key-step Wittig reaction gave the ligand backbones, which were condensed with amino alcohols and then cyclized to obtain the corresponding ligands. These ligands were subsequently applied in the nickel(II)-catalyzed enantioselective fluorination of oxindoles and β-ketoesters to obtain the corresponding products with enantioselectivities of up to >99% ee and high yields. Application of the chiral pincer ligands in the chromium-catalyzed enantioselective Nozaki-Hiyama-Kishi reaction of aldehydes gave the corresponding alcohols with an optimal enantioselectivity of 93%.

Speciation of the nickel(II) complexes with oxalic and malonic acids studied in 1.0 mol dm−3 NaCl at 25°C

In this article, we present the results of the speciation of the binary nickel(II)-oxalic acid (H2L) and nickel(II)-malonic acid (H2L) systems studied by electromotive forces measurements emf (H) using 1.0 mol dm−3 NaCl as the ionic medium at 25°C. The experimental data were analyzed by a computational least-squares program LETAGROP/FONDO, a version of the LETAGROP program, written to analyze regular formation function and reduced formation functions, taking into account the hydrolysis of the nickel(II) cation and the acid base reactions of the ligands which were kept fixed during the analysis. In the nickel(II)-oxalic acid system the complexes [NiHL]+, [NiL], [Ni(OH)L]−, and [NiL2]2− were observed and for the nickel(II)-malonic acid system the complexes [NiHL]+, [NiL], [Ni(OH)L]−, and [Ni(OH)2L]2− were detected. The stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.

Optical and colorimetric characteristics of a nickel(II) complex with 1-nitroso-2-naphthol-3,6-disulfonic acid

Optimal conditions for the complexation of nickel(II) with 1-nitroso-2-naphthol-3,6-disulfonic acid were found using the spectrophotometric method. The optimal pH interval for complexation was 7.2–8.8 with a fivefold excess of the reagent. The stoichiometric Me: R composition was 1: 2. The molar absorption coefficient and colorimetric characteristics of the complex were determined in the nickel(II) concentration range of (4.09–16.35) × 10−5 M. The molar absorption coefficient was (7.52 ± 0.05) × 103 (n = 10, P = 0.95). The most sensitive chromaticity functions were B [(1.83 ± 0.04) × 105] and G [(1.76 ± 0.05) × 105] (n = 9, P = 0.95).

Development of Nanostructured Electrochemical Sensor Based on Polymer Film Nickel-Salen for Determination of Dissolved Oxygen

An amperometric oxygen sensor based on a polymeric nickel-salen (salen = N,Ń -ethylenebis(salicydeneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel-salen complex at a platinum electrode in acetonitrile/tetrabuthylamonium perchlorate by cyclic voltammetry. The voltammetric behavior of the modified electrode was investigated in 0.5mol L-1 KCl solution in the absence and presende of molecular oxygen. A significant increased of cathodic peak current (at -0.20 vs. SCE) of the modified electrode with addition of oxygen to the solution was observed. This result shows that the nickel-salen film on the surface of the electrode promotes the reduction of oxygen. The reaction can be brought about electrochemically where in the nickel(II) complex is first reduced to a nickel(I) complex at the electrode surface. The nickel(I) complex then undergoes a catalytic oxidation by the oxygen molecular in solution back to the nickel(II) complex, which can then be electrochemically re-reduced to produce an enhancement of the cathodic current. The plot of the cathodic current versus the dissolved oxygen concentration for chronoamperometry (potential fixed = -0.20V) at the sensor was linear in the concentration range of 3.95 to 9.20mg L-1 with concentration limit of 0.17mg L-1 O2. The modified electrode proposed is useful for the quality control and routine analysis of dissolved oxygen in commercial water and environmental water samples. The results obtained for the levels of dissolved oxygen are in agreement with the results obtained with an O2 commercial sensor.

Preparation of Nickel/Active Carboncatalyst and its Utilization for Benzene Hydrogenation

The research on the preparation of nickel catalyst impregnated on active carbon by two methods has been carried out. The impregnation of Ni metal was done using nickel(II) chloride as a precursor. The impregnated of Ni metal on samples in A method was made in varying of percentage i.e., 0.5, 1.0 and 2.0% (w/w) as the weight proportion of Ni to active carbon and NiCl2.6H20. The concentration of Ni that would be impregnated on samples in B method was made close to Ni content of samples in A method determined by atomic adsorption spectrometry. Preparation of nickel/active carbon catalyst with A method was done with dipping the active carbon in the nickel(II) chloride solution followed by filtering and then drying at 110 °C for 4 hours, and then calcination by flowing nitrogen and reduction by hydrogen, each at 400 °C at 4 hours. The treatments made on samples in A method was also done on samples in B method, the only difference was evaporating all of precursor solution after dipping active carbon in that precursor solution was done in B method. The characterization includes: iodium adsorption test, determination of nickel content by means of atomic adsorption spectrometry, and acidity by adsorption of ammonia methods. Test of catalyst activity was done by means of hydrogenation of benzene to cyclohexane at 150, 200 and 250 °C, the pressure of 1 atm and the flow rate of hydrogen 6 mL/minute. The products were analyzed by gas chromatographic method. The results show that A method produced a catalyst with relatively low nickel content. However the acidity and ability to convert benzene to cyclohexane were relatively high and it increased as increasing the content of nickel. The temperature of the reaction was achieved at 250 °C which gave the yield on conversion of 25.3678%. The catalyst obtained by B method in the same condition of hydrogenation gave only smaller results.

Nickel(II) complexes of the multihistidine peptide fragments of human prion protein

Nickel(II) complexes of the peptide fragments of human prion protein containing histidyl residues both inside and outside the octarepeat domain have been studied by the combined application of potentiometric, UV–visible and circular dichroism spectroscopic methods. The imidazole-N donor atoms of histidyl residues are the exclusive metal binding sites below pH 7.5, but the formation of stable macrochelates was characteristic only for the peptide HuPrP(76–114) containing four histidyl residues. Yellow colored square planar complexes were obtained above pH 7.5–8 with the cooperative deprotonation of three amide nitrogens in the [N im,N −,N −,N −] coordination mode. It was found that the peptides can bind as many nickel(II) ions as the number of independent histidyl residues. All data supported that the complex formation processes of nickel(II) are very similar to those of copper(II), but with a significantly reduced stability for nickel(II), which shifts the complex formation reactions into the slightly alkaline pH range. The formation of coordination isomers was characteristic of the mononuclear complexes with a significant preference for the nickel(II) binding at the histidyl sites outside the octarepeat domain. The results obtained for the two-histidine fragments of the protein, HuPrP(91–115), HuPrP(76–114)H85A and HuPrP(84–114)H96A, made it possible to compare the binding ability of the His96 and His111 sites. These data reveal a significant difference in the nickel(II) and copper(II) binding sites of the peptides: His96 was found to predominate almost completely for nickel(II) ions, while the opposite order, but with comparable concentrations, was reported for copper(II).

Magnetic and structural studies of novel tetranickel hydroxamates

The dinickel(II) compound [Ni 2(μ-OAc) 2(OAc) 2(μ-H 2O)(asy·dmen) 2]·2.5H 2O, 1; undergoes facile reaction in a 1:2 molar ratio with benzohydroxamic acid (BHA) in ethanol to give the novel nickel(II) tetranuclear hydroxamate complex [Ni 4(μ-OAc) 3(μ-BA) 3(asy·dmen) 3][OTf] 2·H 2O, 2, in which the bridging acetates, bridging two nickel atoms in 1, undergo a carboxylate shift from the μ 2-η 1:η 1 bridging mode of binding to the μ 3-η 1:η 2 bridging three nickel atoms in the tetramer. The structure of complex 2 was determined by single-crystal X-ray crystallography. The two monodentate acetates, water and two bidentate bridging acetates of two moles of complex 1 are replaced by three monodentate bridging acetates and three benzohydroxamates. Three nickel atoms in the tetramer, Ni(2), Ni(3) and Ni(4) are in a N 2O 4 octahedral environment, while the fourth nickel atom Ni(1) is in an O(6) octahedral environment. The Ni–Ni separations are Ni(1)–Ni(2) = 3.108 Å, Ni(1)–Ni(3) = 3.104 Å and Ni(1)–Ni(4) = 3.110 Å, which are longer than previously studied in dinuclear urease inhibited models but shorter than in the nickel(II) tetrameric glutarohydroxamate complex [Ni 4(μ-OAc) 2(μ-gluA 2) 2(tmen) 4][OTf] 2, isolated and characterized previously in this laboratory. Magnetic studies of the tetrameric complex show that the four Ni(II) ions are ferromagnetically coupled, leading to a total ground spin state S T = 4. Three analogous tetranuclear nickel hydroxamates were prepared from AHA and BHA and the appropriate dinuclear complex with either sy·dmen or asy·dmen as capping ligands.