Mononuclear Nickel Research Articles

A Nickel(II) Complex as a Homogeneous Electrocatalyst for Water Oxidation at Neutral pH: Dual Role of HPO42− in Catalysis

AbstractA new mononuclear nickel complex, featuring two cis‐relative labile sites, is reported as a homogeneous electrocatalyst for water oxidation in a neutral phosphate buffer. The water oxidation catalysis can be initiated at a moderate overpotential of approximately 0.48 V. Mechanistic studies reveal that the oxidation of water by a two‐electron oxidized species of the nickel catalyst is feasible, with formation of a peroxide intermediate through intramolecular O−O coupling. Interestingly, it has been found that the buffer base (HPO42−) plays a dual role in the catalytic system: it acts as a proton acceptor to expedite proton‐coupled electron transfer (PCET) during catalysis, but it also suppresses the electrocatalysis through an anation process.

Di(carbene)-Supported Nickel Systems for CO2 Reduction Under Ambient Conditions

Di(carbene)-supported nickel species 1 and 2 are efficient catalysts for the room-temperature reduction of CO2 to methanol in the presence of sodium borohydride. The catalysts feature unusual stability, particularly for a base metal catalyst, enabling >1.1 million turnovers of CO2. Moreover, while other systems involve more expensive reducing reagents, sodium borohydride is inexpensive and easily handled. Furthermore, effecting reduction in the presence of water enables direct access to methanol. Preliminary mechanistic data collected are most consistent with a mononuclear nickel active species that mediates rate-determining reduction of a boron formate.

Mononuclear nickel (II) and copper (II) coordination complexes supported by bispicen ligand derivatives: Experimental and computational studies

The synthesis, characterization and density functional theory calculations of mononuclear Ni and Cu complexes supported by the N,N′-dimethyl-N,N′-bis-(pyridine-2-ylmethyl)-1,2-diaminoethane ligand and its derivatives are reported. The complexes were characterized by X-ray crystallography as well as by UV−visible absorption spectroscopy and EPR spectroscopy. The solid state structure of these coordination complexes revealed that the geometry of the complex depended on the identity of the metal center. Solution phase characterization data are in accord with the solid phase structure, indicating minimal structural changes in solution. Optical spectroscopy revealed that all of the complexes exhibit color owing to d-d transition bands in the visible region. Magnetic parameters obtained from EPR spectroscopy together with other structural data suggest that the Ni(II) complexes are in a pseudo-octahedral geometry and Cu(II) complexes are in a distorted square pyramidal geometry. In order to understand in detail how ligand sterics and electronics affect complex topology detailed computational studies were performed. The series of complexes reported in this article will add significant value in the field of coordination chemistry as Ni(II) and Cu(II) complexes supported by tetradentate pyridyl based ligands are rather scarce.

Spectroscopically Characterized Synthetic Mononuclear Nickel-Oxygen Species.

Iron, copper, and manganese are the predominant metals found in oxygenases that perform efficient and selective hydrocarbon oxidations and for this reason, a large number of the corresponding metal-oxygen species has been described. However, in recent years nickel has been found in the active site of enzymes involved in oxidation processes, in which nickel-dioxygen species are proposed to play a key role. Owing to this biological relevance and to the existence of different catalytic protocols that involve the use of nickel catalysts in oxidation reactions, there is a growing interest in the detection and characterization of nickel-oxygen species relevant to these processes. In this Minireview the spectroscopically/structurally characterized synthetic superoxo, peroxo, and oxonickel species that have been reported to date are described. From these studies it becomes clear that nickel is a very promising metal in the field of oxidation chemistry with still unexplored possibilities.

Synthesis, structural characterization and DFT calculation on a square-planar Ni(II) complex of a compartmental Schiff base ligand

Reaction of a symmetric compartmental Schiff-base ligand, (H2L) with nickel(II) perchlorate hexahydrate in 1:1 M ratio in methanol gives rise to a mononuclear nickel(II) compound, NiL (1). The compound has been characterized by C, H, N microanalyses and UV–Vis spectra. The single crystal X-ray diffraction studies reveal a square planar geometry around the Ni(II) center. The compound crystallizes in monoclinic system with space group C2/c with a = 21.6425(6), b = 9.9481(3), c = 13.1958(4) Å, β = 107.728(2)°, V = 2706.16(14) Å3 and Z = 4. Ground state DFT optimization and TDDFT calculations on the ligand and complex were performed to get their UV–Vis spectral pattern.

Syntheses and crystal structures of copper(II) and nickel(II) complexes derived from 2-bromo-4-chloro-6-[(2-methylaminoethylimino)methyl]phenol

A new centrosymmetric mononuclear copper(II) complex [Cu(L)2](ClO4)2 (I) and a new centrosymmetric mononuclear nickel(II) complex [Ni(L)2(MeOH)2](ClO4)2 (II), where L is the zwitterionic ligand 2-bromo-4-chloro-6-[(2-methylammonioethylimino)methyl]phenolate, have been prepared from the Schiff base 2-bromo-4-chloro-6-[(2-methylaminoethylimino)methyl]phenol with copper perchlorate and nickel perchlorate, respectively. The complexes were characterized by elemental analysis, infrared spectra, and single-cyrstal X-ray diffraction (CIF files CCDC nos. 1408054 (I) and 1407973 (II)). Complex I crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 7.7736(4), b = 21.608(1), c = 8.5194(4) A, β = 93.907(2)°, V = 1427.7(1) A3, Z = 2, R1 = 0.0546, and wR2 = 0.1531. Complex II crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 21.324(3), b = 16.821(2), c = 9.425(1) A, β = 90.114(2)°, V = 3380.5(7) A3, Z = 4, R1 = 0.0693, and wR2 = 0.1627. The Cu atom in I is in square planar coordination, and the Ni atom in II is in octahedral coordination.

A mononuclear nickel(II) complex based on polypyridyl ligand: synthesis, characterization, and biological activity

[Ni(acac)2(o-NPIP)](CH3OH)3 (acac = acetylacetonate), based on the polypyridyl ligand 2-(2-nitrophenyl)imidazo[4,5-f]1,10-phenanthroline) (o-NPIP), has been synthesized and characterized by single-crystal analysis, IR and electronic spectra. In the structure of Ni(II) complex, the coordination sphere around Ni(II) is distorted octahedral with one o-NPIP and two acetylacetonates. DNA binding and human serum albumin (HSA) interactions with the Ni(II) complex have been investigated by electronic absorption and fluorescence measurements, revealing that the Ni(II) complex binds with DNA via intercalative binding. The quenching constants verified a dynamic quenching mechanism between HSA and the Ni complex by fluorescence quenching. ΔG, ΔH, and ΔS at different temperatures (288, 298, and 310 K) indicated that hydrophobic interactions play a major role. Synchronous fluorescence spectral experiments revealed that the Ni(II) complex affected the microenvironment around the tryptophan residue of HSA.

Synthesis, Crystal Structure, and Photophysical Properties of Nickel Complex From Triphenylamine Schiff Base Ligand

A novel Schiff base ligand L and its mononuclear nickel complex Ni(L)2(SCN)2 were designed, synthesized and characterized by elemental analysis, IR spectra, MS, 1H-NMR spectroscopy, and single-crystal X-ray diffraction analysis. The crystals of L and Ni(L)2(SCN)2 belong to orthorhombic crystal system with the space group of P212121 for L and Pbcn for Ni(L)2(SCN)2, respectively. The center atom Ni(II) is coordinated with six nitrogen atoms in a distorted octahedron coordination environment. The four N atoms of them are from the two independent ligands and the other two nitrogen atoms from two SCN−. Their photophysical properties of the ligand and its Ni(II) complex were investigated and interpreted on the basis of theoretical calculations (TD-DFT).

Structures and spectroscopic properties of Ni(II) and Mn(II) complexes based on 5-(3′, 5′-dicarboxylphenyl) picolinic acid ligand

Two novel complexes including [Ni(Hdcppa)(H2O)4] (1) and {[Mn3(dcppa)2(H2O)6]·2H2O}n (2) have been synthesized and characterized by single crystal X-ray structure analysis and elemental analysis. Results show that 1 is a mononuclear nickel(II) compound with octahedron coordination geometry, while 2 is a stairs-like 2D layer structure consisting of the trinuclear MnII units linked through dcppa3−. Spectroscopic and electrochemical properties of the complexes 1–2 have also been studied in dimethyl sulfoxide solution at room temperature.

A mononuclear nickel(II) complex and a dinuclear manganese(III) complex derived from N,N'-bis(5-methoxysalicylidene)-1,2-ethanediamine: synthesis, crystal structures, and catalytic epoxidation property

A mononuclear nickel(II) complex and a dinuclear manganese(III) complex derived from N,N'-<i>bis</i>(5-methoxysalicylidene)-1,2-ethanediamine: synthesis, crystal structures, and catalytic epoxidation property

A mononuclear nickel(II) complex and a dinuclear manganese(III) complex derived from N,N'-bis(5-methoxysalicylidene)-1,2-ethanediamine: Synthesis, crystal structures and catalytic epoxidation property

Synthesis and characterization of a mononuclear nickel(II) complex [NiL] · CH3OH (I) and a dinuclear manganese(III) complex [Mn2L2(NCS)2] (II) derived from the bis-Schiff base N,N'-bis(5-methoxysalicylidene)-1,2-ethanediamine (H2L) are reported. The complexes were characterized by elemental analyses, IR spectra and molar conductivity. Single crystal X-ray structures of the complexes have been determined (CIF files CCDC nos. 1056778 (I) and 1056688 (II)). The Ni atom in I is in a square planar coordination, and the Mn atom in II is in an octahedral coordination. Catalytic property for epoxidation of styrene by the complexes using PhIO and NaOCl as oxidant has been studied. As a result, complex II is efficient for the styrene epoxidation.

Syntheses, characterization and crystal structures of [Ni(La)2] and [Zn(Lb)(N3)(Amp)

A new centrosymmetric mononuclear nickel(II) complex, [Ni(La)2] (I), and a new mononuclear zinc(II) complex, [Zn(Lb)(N3)(AMP)] (II) (La = 2-iminomethyl-4-methylphenolate, Lb = 4-methyl-2-[(4-methylpyridin-2-ylimino)methyl]phenolate, AMP = 2-amino-4-methylpyridine), have been prepared and characterized by elemental analysis, IR and UV-Vis spectra, and single-cyrstal X-ray diffraction (CIF files CCDC nos. 1059023 (I) and 1059024 (II)). Complex I crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 16.067(2), b = 5.7222(6), c = 7.9004(9) A, β = 92.471(4)°, V = 725.7(1) A3, Z = 2, R1 = 0.0298, and wR2 = 0.0695. Complex II crystallizes in the triclinic space group \(P\bar 1\) with unit cell dimensions a = 7.649(1), b = 10.414(2), c = 13.903(3) A, α = 106.896(2)°, β = 91.581(2)°, γ = 103.033(2)°, V = 1027.3(4) A3, Z = 2, R1 = 0.0372, and wR2 = 0.0823. The Ni atom in I is in a square planar coordination, and the Zn atom in II is in a tetrahedral coordination. Crystals of the complexes are stabilized by hydrogen bonds and p···p interactions.

Synthesis and structures of nickel(II) complexes with xanthurenate ions

The reaction of nickel(II) chloride with xanthurenic acid afforded two crystalline products, [Ni(HXan)2(H2O)4]·6H2O (1) and [Ni3(Xan)2(H2O)10][Ni(Xan)2]·4{(CH3)2CO}·2H2O (2), with HXan− and Xan2− standing for the deprotonated forms of the acid. Both compounds were unambiguously characterized by means of X-ray structure analysis. Their solid state structures give evidence of a presence of different xanthurenate ions and their tautomeric forms in the solution. Compound 1 is a mononuclear nickel(II) complex with metal ion in a nearly octahedral environment of six ligands: four aqua ligands and two trans positioned HXan− ions, each coordinated in a monodentate manner via a carboxylate oxygen. Compound 2 consists of trinuclear complex cations [Ni3(Xan)2(H2O)10]2+ and mononuclear complex anions [Ni(Xan)2]2−. The Xan2− ions of the complex ions in 2 are not the same, they differ in the position of the ionized hydroxyl moiety. With both compounds possessing several hydrogen bond donors and acceptors, intricate patterns of intramolecular connectivity may be observed in their solid state structures.

Synthesis and Crystal Structure of the Mononuclear Nickel Complex [Me2CHN(PPh2)2]Ni(SCH2Ph)2

The mononuclear nickel complex [Me2CHN(PPh2)2]Ni(SCH2Ph)2 has been synthesized by the reaction of [Me2CHN(PPh2)2]NiCl2 with PhCH2SH and Et3N in CH2Cl2 in 77% yield. The title complex was structurally characterized by 1H NMR, 31P{1H} NMR spectroscopy as well as X-ray crystallography. The X-ray diffraction analysis reveals that the molecular structure consists of a central nickel atom coordinated by two phosphorus atoms of the bis(diphenylphosphanyl)amine and two sulfur atoms of benzylthiolate. There are no classical hydrogen bonds but van der Waals’ interactions exist to stabilize the solid state in the crystal packing.

Synthesis and structural characterization of two half-sandwich nickel(II) complexes with the scorpionate ligands

The synthesis and characterization of two new halfsandwich mononuclear nickel(II) complexes with the scorpionate ligands, [k3-N, N',N''-Tpt-Bu, MeNiI] (1) and [k3-N,N',N''-Tpt-Bu, MeNiNO3] (2), are reported. These complexes have been fully characterized by elemental analyses and infrared spectra. Their molecular structures were determined by single crystal X-ray diffraction. The nickel(II) ion of complex 1 is in a four-coordinate environment, in which the donor atoms are provided by three nitrogen atoms of a hydrotris(pyrazolyl) borate ligand and one iodide atom, while that of complex 2 is in a five-coordinate environment with three nitrogen atoms from a hydrotris(pyrazolyl)borate ligand and two oxygen atoms from a nitrate ion.

SYNTHESIS, CRYSTAL STRUCTURES AND PRELIMINARY ANTIBACTERIAL ACTIVITIES OF NICKEL(II) AND ZINC(II) COMPLEXES DERIVED FROM 2-BROMO-6-[(3-CYCLOHEXYLAMINOPROPYLIMINO) METHYL]PHENOL

ABSTRACT Two centrosymmetric mononuclear nickel(II) and zinc(II) complexes, [NiL 2 ]∙2NO 3 (1) and [ZnL 2 (dca) 2 ] (2), where L is the zwitterionic form of 2-bromo-6-[(3-cyclohexylaminopropylimino)methyl]phenol, and dca is the dicyanamide anion, have been synthesized. The complexes have been characterized by physico-chemical methods and single crystal X-ray determination. Complex (1) crystallizes in the monoclinic space group P 2 1 / n with unit cell dimensions a = 7.0091(7) A, b = 11.137(1) A, c = 23.997(2) A, β = 97.390(3)°, V = 1857.7(3) A 3 , Z = 2, R 1 = 0.0617, and wR 2 = 0.1632. Complex (2) crystallizes in the triclinic space group P -1 with unit cell dimensions a = 8.762(1) A, b = 10.386(1) A, c = 10.687(2) A, α = 85.209(2)°, β = 83.931(2)°, g = 88.734(2)°, V = 963.6(2) A 3 , Z = 1, R 1 = 0.0374, and wR 2 = 0.0873. The Ni atom in (1) is in a square planar geometry, and the Zn atom in (2) is in an octahedral geometry. The preliminary antibacterial activities of the complexes were assayed.

Nickel(II) complexes having different configurations controlled by N,N,O-donor Schiff-base ligands in presence of isothiocyanate as co-ligand: Synthesis, structures, comparative biological activity and DFT study

Four mononuclear nickel(II) complexes, viz. [NiL1(OAc)(H2O)2]·2H2O (1), [NiL1(NCS)(H2O)2]·H2O (1a), [NiL2(OAc)(H2O)] (2), and [NiL2(NCS)] (2a) (where HL1=2-[(2-Morpholin-4-yl-ethylimino)-methyl]-phenol and HL2=2-[(2-Pyrrolidin-1-yl-ethylimino)-methyl]-phenol) have been synthesized and structurally characterized. Single crystal X-ray analysis reveals the presence of square planar coordination geometry about nickel for 2a, whereas others have distorted octahedral geometry. DFT calculations have done to explore the origin of different geometries of 1a and 2a although their preparative procedure is same. The influence of different geometries i.e., octahedral and square-planar on the anticancer activity of Ni(II) have been investigated on Erhlich’s ascities carcinoma (EAC) cells and the order of anticancer activity is 2a>1a>2>1. The biological results are further compared to the activity of cis-platin.

Synthesis and Crystal Structure of Mononuclear Nickel Ethanedithiolate Complex with 1,2-bis(diphenylphosphino)ethane

The title complex (dppe)Ni(edt) [dppe = 1,2-bis(diphenylphosphino)ethane, edt = ethanedithiolate] was prepared by treatment of (dppe)NiCl2 with HSCH2CH2SH in the presence of Et3N in CH2Cl2 at room temperature and structurally characterized by 1H NMR, 31P{1H} NMR, 13C{1H} NMR and ESI-MS spectroscopy. In addition, the molecular structure was determined by single crystal X-ray diffraction analysis. The title complex consists of a distorted square planar NiP2S2 core coordinated by dppe and edt. The van der Waals’ interactions stabilize the solid state in the crystal packing.

Steric Effect on the Nucleophilic Reactivity of Nickel(III) Peroxo Complexes.

A set of nickel(III) peroxo complexes bearing tetraazamacrocyclic ligands, [Ni(III)(TBDAP)(O2)](+) (TBDAP = N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) and [Ni(III)(CHDAP)(O2)](+) (CHDAP = N,N'-dicyclohexyl-2,11-diaza[3.3](2,6)pyridinophane), were prepared by reacting [Ni(II)(TBDAP)(NO3)(H2O)](+) and [Ni(II)(CHDAP)(NO3)](+), respectively, with H2O2 in the presence of triethylamine. The mononuclear nickel(III) peroxo complexes were fully characterized by various physicochemical methods, such as UV-vis, electrospray ionization mass spectrometry, resonance Raman, electron paramagnetic resonance, and X-ray analysis. The spectroscopic and structural characterization clearly shows that the NiO2 cores are almost identical where the peroxo ligand is bound in a side-on fashion. However, the different steric properties of the supporting ligands were confirmed by X-ray crystallography, where the CHDAP ligand gives enough space around the Ni core compared to the TBDAP ligand. The nickel(III) peroxo complexes showed reactivity in the oxidation of aldehydes. In the aldehyde deformylation reaction, the nucleophilic reactivity of the nickel(III) peroxo complexes was highly dependent on the steric properties of the macrocyclic ligands, with a reactivity order of [Ni(III)(TBDAP)(O2)](+) < [Ni(III)(CHDAP)(O2)](+). This result provides fundamental insight into the mechanism of the structure (steric)-reactivity relationship of metal peroxo intermediates.

Syntheses, structures and magnetic properties of two mononuclear nickel(II) complexes based on bicarboxylate ligands

AbstractTwo new complexes, [Ni(pydc)(H2O)3] (1) and [Ni(cma)(H2O)3] (2) (H2pydc = pyridine-2,6-dicarboxylic acid, H2cma = 2-(carboxymethoxy)benzoic acid), have been synthesized and structurally characterized. In both compounds, NiIIis surrounded by one tridentate chelate dianionic ligand (pydc2ˉ for1and cma2ˉ for2) and three coordinated water molecules in a distorted octahedral geometry (NiNO5for1and NiO6for2). The magnetic properties for1and2have been discussed in detail.