Tetranuclear Nickel Complex 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.

On the Concurrent Bipartite Entanglement of a Spin-1 Heisenberg Diamond Cluster Developed for Tetranuclear Nickel Complexes

The bipartite entanglement of a quantum spin-1 Heisenberg diamond cluster in the presence of the external magnetic field is quantified through the negativity, which is calculated for spin pairs from a diagonal and a side of the diamond spin cluster taking into consideration two different coupling constants. The magnetic field may cause a few crossings of energy levels of the spin-1 Heisenberg diamond cluster, which is responsible at low enough temperatures for a stepwise dependence of the negativity on the magnetic field accompanied with a drop of the negativity at respective magnetic-field-driven transitions due to emergence of mixed states. It is shown that the bipartite entanglement between spin pairs on a diagonal and a side of the diamond spin cluster is concurrent although they may eventually become both nonzero albeit not fully saturated. It is predicted that the tetranuclear nickel complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 (aetpy = 2-aminoethyl-pyridine), which represents an experimental realization of the spin-1 Heisenberg diamond cluster with two different antiferromagnetic coupling constants, exhibits a substantial bipartite entanglement between two spin-1 Ni2+ magnetic ions from a shorter diagonal of the diamond spin cluster up to temperatures approximately about 50 K and up to magnetic fields about 70 T.

Synthesis of novel tetranuclear Ni complex incorporated mesoporous silica for improved photocatalytic degradation of methylene blue in presence of visible light

Tetranuclear nickel complex, [Ni4(LH)4]·CH3CN (I) (LH3 = (E)-2-(hydroxymethyl)-6-(((2-hydroxyphenyl)imino)methyl)phenol)) was synthesized and characterized by single-crystal X-ray analysis. The synthesized mesoporous material was functionalized with organic acid and then tetranuclear Ni complex was incorporated into the modified materials. The characterization of the catalysts were done by powder XRD, FT-IR, TGA, ICP, SEM etc. to have insight into the structural integrity, existence of guest entities in the materials, and other vital parameters. The rise in the activities in photocatalysis was observed after immobilization of the Ni complex onto the surface of acid-functionalized porous materials. The prepared materials were found to be highly active in the degradation of methylene blue (MB) and showed a maximum 92 % degradation in a very short time (15 min) with Ni complex incorporated acid-functionalized MCM-48. The prepared materials are robust in nature and recyclable up to the 4th cycle with good degradation.

Solvent mediated synthesis of homoleptic tri and tetranuclear nickel complex derived from [Ni2(µ-SeC5H4N)2(dppe)2]2+ and theoretical studies

In the present report, the reactivity of the binuclear complex [Ni2(µ-SeC5H4N)2(dppe)2]2+ towards dichloromethane and methanol has been studied. The complex [Ni2(µ-SeC5H4N)2(dppe)2]2+ in the presence of chlorinated solvent resulted in selenido bridged trinuclear complex of composition [Ni3(µ-Se)2(dppe)2]2+ (1) whereas in the presence of methanol hydrolyzed product having cubane core [Ni4{(C5H4N)2Se}4(μ3OH)4(C6H5COO)(HCOO)]2+ (2) was isolated. Both the complexes were characterized by elemental analysis, IR, 1H, and 31P{1H} NMR spectroscopy. An attempt has also been made to investigate their thermal studies. The molecular structure of both the complex [Ni3(µ-Se)2(dppe)2]2+ (1) and [Ni4{(C5H4N)2Se}4(μ3OH)4(C6H5COO)(HCOO)]2+ (2) were established by single-crystal X-ray diffraction analysis. Broken-symmetry density functional theory (BS-DFT) calculations were carried out on complex 2 to investigate the electronic structure and nature of magnetic exchange interaction. BS-DFT reveals the existence of three different J values i.e. -8.9 cm−1, +18.7 cm−1 and +1.8 cm−1 between different Ni(II) pairs. A strong ferromagnetic interaction was observed between formate/phenylacetate bridged Ni(II) centers. An antiferromagnetic interaction between the ferromagnetically coupled formate and phenylacetate bridged Ni(II) dimers result in isolation of S = 0 spin ground state for complex 2. Molecular orbital, spin-density analyses were performed on the X-ray and optimized geometries to probe the electronic structure of complex 2.

Direct copolymerization of ethylene with protic comonomers enabled by multinuclear Ni catalysts

Ethylene/polar monomer coordination copolymerization offers an attractive way of making functionalized polyolefins. However, ethylene copolymerization with industrially relevant short chain length alkenoic acid remain a big challenge. Here we report the efficient direct copolymerization of ethylene with vinyl acetic acid by tetranuclear nickel complexes. The protic monomer can be extended to acrylic acid, allylacetic acid, ω-alkenoic acid, allyl alcohol, and homoallyl alcohol. Based on X-ray analysis of precatalysts, control experiments, solvent-assisted electrospray ionization-mass spectrometry detection of key catalytic intermediates, and density functional theory studies, we propose a possible mechanistic scenario that involves a distinctive vinyl acetic acid enchainment enabled by Ni···Ni synergistic effects. Inspired by the mechanistic insights, binuclear nickel catalysts are designed and proved much more efficient for the copolymerization of ethylene with vinyl acetic acid or acrylic acid, achieving the highest turnover frequencies so far for both ethylene and polar monomers simultaneously.

Synthesis, IR spectroscopic and structural studies of erbium and nickel complexes with N,N'-tetraethyl-N''-trifluoroacetylphosphoroustriamide

A synthesis procedure was developed and a new carbacylamidophosphate type ligand N,N'-tetraethyl-N''-trifluoroacetylphosphoroustriamide (CF3C(O)NHP(O)(NC2H5)2, HL) that contains C(O)NP(O) chelating fragment was isolated in the crystalline state. A mononuclear erbium complex [Er(HL)3(NO3)3] and a tetranuclear nickel complex [Ni4L4(OCH3)4(CH3OH)4] were isolated in the crystalline state. The suggestion about the type and coordination mode of the ligand in complexes was made based on IR spectroscopic investigations: deprotonated (acido-) form in bidentate manner in nickel complex and neutral form in monodentate manner in erbium complex. According to X-ray structural studies, different coordination modes of the ligand in complexes were determined: bidentate chelate manner via the oxygen atoms of the phosphoryl and carbonyl groups of the ligand with the formation of six-membered chelate cycles in case of nickel complex and monodentate manner via the oxygen atom of the phosphoryl group of the ligand in case of erbium complex, the coordination polyhedron of which was interpreted as a distorted three-handed trigonal prism.

Effect of uniaxial single-ion anisotropy on a stability of intermediate magnetization plateaus of a spin-1 Heisenberg diamond cluster

Ground-state phase diagrams and magnetization curves of a spin-1 Heisenberg diamond cluster with two different coupling constants and uniaxial single-ion anisotropy are investigated in a presence of the external magnetic field with the help of exact diagonalization methods. It is shown that the spin-1 Heisenberg diamond cluster exhibits several remarkable quantum ground states, which are manifested in zero- and low-temperature magnetization curves as intermediate plateaus at one-quarter, one-half and three-quarters of the saturation magnetization. It is found that the width of the fractional magnetization plateaus depends basically on a relative strength of the coupling constants as well as uniaxial single-ion anisotropy, which may substantially shrink or even cause full breakdown of some intermediate magnetization plateaus. It is evidenced that a relatively weak uniaxial single-ion anisotropy of the easy-axis type considerably improves a theoretical fit of low-temperature magnetization curves of the tetranuclear nickel complex [Ni4 (μ-CO3)2(aetpy)8](ClO4)4 in a low-field region without spoiling the previous fit based on the fully isotropic Heisenberg model in a high-field region.

Novel carbonate/pyridine tetranuclear nickel complex, exhibiting slow relaxation of the magnetization

Tetranuclear [Ni4(CO3)4(pyridine)8·Na]Cl·pyridine·H2O compound with unusual square-planar geometry was obtained via spontaneous fixation of atmospheric CO2 and its conversion into carbonate bridging ligands. This compound exhibits a slow relaxation of the magnetization caused by a spin-glass behaviour.

Two biologically inspired tetranuclear nickel(II) catalysts: effect of the geometry of Ni4 core on electrocatalytic water oxidation.

Two biologically inspired tetranuclear nickel complexes [Ni4(L-H)4(CH3COO)3]·Cl (1) and [Ni4(L-H)4(CH3COO)4]·2CH3OH (2) (L = di(pyridin-2-yl)methanediol) have been synthesized and investigated by a combination of X-ray crystallography, PXRD, electrochemistry, in-situ UV-Vis spectroelectrochemistry and DLS. Both of the two complexes feature a core composed of four Ni(II) ions with the same peripheral ligation provided by the anionic di(pyridin-2-yl)methanediol and MeCOO- ligands. Whereas, complex 1 possesses one distorted cubane-like [Ni4(µ3-O)4] core, while 2 has one extended butterfly-like [Ni4(µ3-O)2] core. The homogeneous electrocatalytic reactivity of the two water-soluble complexes for water oxidation have been thoroughly studied, which demonstrates that both of them can efficiently electrocatalyze water oxidation with high stability under alkaline conditions, at relatively low over-potentials (η) of 420-790mV for 1 and 390-780mV for 2, both in the pH range of 7.67-12.32, with the high TOF of about 139s-1 (1) and 69s-1 (2) at pH = 12.32, respectively. By a series of comparative experiments for complexes 1 and 2, we proposed that their crystal geometries play an important role in their electrocatalytic reactivity for water oxidation. We verified that biomimetic cubane geometry could promote OER catalysis with two very similar compounds for the first time. Compared with 2, the biomimetic cubane topology of 1 could promote OER catalysis by facilitating efficient charge delocalization and electron-transfer.

Insights into Nature of Magnetization Plateaus of a Nickel Complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 from a Spin-1 Heisenberg Diamond Cluster

Magnetic and magnetocaloric properties of a spin-1 Heisenberg diamond cluster with two different coupling constants are investigated with the help of an exact diagonalization based on the Kambe’s method, which employs a local conservation of composite spins formed by spin-1 entities located in opposite corners of a diamond spin cluster. It is shown that the spin-1 Heisenberg diamond cluster exhibits several intriguing quantum ground states, which are manifested in low-temperature magnetization curves as intermediate plateaus at 1/4, 1/2, and 3/4 of the saturation magnetization. In addition, the spin-1 Heisenberg diamond cluster may also exhibit an enhanced magnetocaloric effect, which may be relevant for a low-temperature refrigeration achieved through the adiabatic demagnetization. It is evidenced that the spin-1 Heisenberg diamond cluster with the antiferromagnetic coupling constants J1/kB = 41.4 K and J2/kB = 9.2 K satisfactorily reproduces a low-temperature magnetization curve recorded for the tetranuclear nickel complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 (aetpy = 2-aminoethyl-pyridine) including a size and position of intermediate plateaus detected at 1/2 and 3/4 of the saturation magnetization. A microscopic nature of fractional magnetization plateaus observed experimentally is clarified and interpreted in terms of valence-bond crystal with either a single or double valence bond. It is suggested that this frustrated magnetic molecule can provide a prospective cryogenic coolant with the maximal isothermal entropy change −ΔSM=10.6 J·K−1·kg−1 in a temperature range below 2.3 K.

Mixed valent/geometry, linear, tetranuclear nickel complex bearing ONO pincer ligand exhibiting hitherto unknown ligation mode

A hitherto unknown linear, tetranuclear nickel(II/III) complex possessing both square-planar and pentagonal bipyramidal geometry around the metal ions was obtained from the reaction of ONO pincer ligand (E)-N′-(2-hydroxybenzylidene)acetohydrazide with [NiCl2(PPh3)2] precursor complex in methanol medium. The novel ONO ligand and its nickel complex were characterized by analytical and spectral data. The identity of the tetranuclear complex crystallized in triclinic crystal system with P1¯ space group was confirmed by single-crystal XRD study. Density Functional Theory (DFT) calculations performed for the optimization of the titled nickel complex by considering the presence as well as the absence of coordinated solvent molecules in the input coordinates revealed that the optimized structures are energetically somewhat disfavored but its formation in the experiment could be attributed to the participation of packing forces that stabilizes the molecule it in the solid state.

Tetranuclear nickel complex of dimethylene bridged diiminedioxime containing different hybridizations of nickel (II)

The reaction of ligand 3,3′-(1,4-ethanediyldinitrilo)bis(2-butanone)dioxime (EnH2) with Ni(ClO4)2 yields [Ni(Ni(En))3](ClO4)2 (1). Complex 1 crystallizes in an R-centered trigonal cell with the space group R3¯. The structure consists of an octahedral [Ni(Ni(En))3]2+ cation containing four Ni(II) ions with different hybridizations (dsp2 and sp3d2) and two perchlorate anions. Three dsp2 Ni(II) ions coordinate to three EnH2 ligands via imine nitrogens and oxime nitrogens and the fourth Ni(II) ion octahedrally coordinates to six oxime oxygens of the coordinated EnH2. Accordingly, a three-bladed propeller-like structure is observed. Two kinds of νCN relating to imine and oxime groups are observed at 1623 and 1488cm−1 respectively. The μeff is 3.47 BM. Bands at 413 and 541nm are assigned to d–d transitions in octahedral field and weak band at 477nm is assigned to d–d transition in square planar field. The emission spectrum under the excitation wavelength 305nm shows a broad band with maximum emission wavelength at 350nm.

Synthesis, structure, and catalytic activity of nickel complexes with new chiral binaphthyl-based NHC-ligands

Two new chiral NHC-nickel complexes have been prepared from the reactions between Ni(OAc)2, K2CO3 or K2CO3/NaBPh4, and imidazolium salts 3 or 4, which are derived from (R)-2,2′-diamino-1,1′-binaphthyl. Treatment of mono-imidazolium salt 3 with 1 equiv of Ni(OAc)2 in the presence of K2CO3 in 1,4-dioxane at 105 °C gives, after recrystallization from a CH2Cl2 solution, the chiral bis-ligated nickel complex (3)2Ni (5). Under similar reaction conditions, bis-imidazolium salt 4 affords a tetranuclear nickel complex [{(4)Ni}3Ni](BPh4)2 (6). All compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 3, 5, 6 have been further confirmed by X-ray diffraction analyses. Nickel complexes 5 and 6 show a good (106 g/mol h) norbornene polymerization activity upon activation with methylaluminoxane (MAO), leading to thermally very stable polynorbornenes.

Synthesis and Crystal Structure of Tetranuclear Nickel Complex Derived from a N-(3-Methoxy-2-hydroxybenzyl)glycine Ligand

Synthesis and Crystal Structure of Tetranuclear Nickel Complex Derived from a N-(3-Methoxy-2-hydroxybenzyl)glycine Ligand

A new tetranuclear nickel complex based on the benzimidazole ligand for the controllable polymerization of methyl methacrylate

Abstract The new tetranuclear [Ni4(L)6Cl]⋅ Cl (1) complex from the benzimidazole-based ligand HL (HL: 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyohenol) was prepared and structurally characterized by EA, FT-IR and X-ray single-crystal diffraction. The tetranuclear complex 1 was shown to efficiently catalyze the controllable polymerization of methyl methacrylate (MMA) in activation with AIBN (azobisisobutyronitrile), giving the syndio-enriched atactic PMMAs. The existence of two active species in the 1/AIBN systems should be favorable for the higher catalytic activities, while the cooperative interactions between the two active centers should result in the relatively broad molecular weight distributions for the obtained PMMAs.

Bis[μ3-N′-oxidopyridine-2-carboximidamidato(2−)]bis[μ2-N′-oxidopyridine-2-carboximidamidato(1−)]tetrapyridinetetranickel(II) dinitrate

The title compound, [Ni4(C6H5N3O)2(C6H6N3O)2(C5H5N)4](NO3)2, is a tetra­nuclear nickel complex containing a single-decker cation, located on an inversion center. The two unique NiII cations are N,N′,N′′,O-chelated by carbox­imid­amid­ate(2−) and carboximidamidate(1−) anions, forming a distorted four-coordinate planar structure, while the other two NiII atoms are N,N′,O,O′-chelated by the same bridging ligands and two pyridine mol­ecules, affording six-coordinated metals in an octa­hedral geometry. The cation is isostructural with the complex crystallized with perchlorate counter-ions in place of nitrate.

Three azido-, alk/phenoxido- and acetato-bridged tetranuclear nickel complexes featuring defective double-cubane

Three new tetranuclear nickel(II) complexes of general formula [Ni 4(L) 2(N 3) 2(CH 3COO) 2(CH 3O) 2] 2· xCH 3OH· yH 2O (HL = HL 1, HL 2 and HL 3; x = 0, y = 1 for 1; x = 2, y = 0 for 2 and x = 2, y = 4 for 3) were synthesized and characterized by single crystal X-ray diffraction and magnetic measurements. Single crystal X-ray studies reveal that all three complexes exhibit similar tetranuclear face-shared defective double-cubane structure, having azido-, alk/phenoxido- and acetato-bridges. Magnetic susceptibility measurements on the complexes in the range of 300–2 K indicate ferromagnetic coupling between the metal ions. The slightly different magnetic behaviors observed are probably caused by subtle structural differences between the respective [Ni 4O 4N 2] cores induced by ligand variation.

Bioinspired Catalytic Conjugate Additions of Thiophenols to α,β-Enones by a Disubstituted Benzoate-Bridged Nickel Mimic for the Active Site of Urease

A disubstituted benzoate polydentate ligand, 2,6-bis[bis(pyridinyl-2-methyl)aminoethoxyl]benzoate (HL), was prepared to synthesize nickel mimics for the active site of urease. Reaction of the deprotonated L− with Ni(ClO4)2·6H2O afforded a dinickel complex, [LNi2(CH3CN)(THF)](ClO4)3 (1), characterized by UV/vis spectroscopy and X-ray crystallography. Addition of urea to an acetonitrile solution of 1 afforded a dinickel urea adduct, [LNi2(urea)2](ClO4)3·2CH3CN (2), which was structurally and spectroscopically characterized. 1H NMR and ESI-MS spectra of 2 both evidenced that urea molecules remained coordinated to the nickel centers of 2 in solution. With the inspiration of urea coordination to the nickel centers of 1, the conjugate additions of thiophenols to α,β-enones catalyzed by complex 1 were examined and found to proceed in good yields. In contrast, the same catalytic reaction by Ni(ClO4)2·6H2O and HL was far less effective. Also, addition of NaOAc or NaOAcPh2 to an acetonitrile solution of 1 gave tetranuclear nickel complexes, [LNi2(μ-OAc)]2(ClO4)4·3H2O (3) and [LNi2(μ-OAcPh2)]2(ClO4)4·5CH3CN·2THF (4), and their molecular structures determined by X-ray diffraction can be described as dimers of dimers. Each dinickel core of 3 and 4 closely mimics the active site of urease. The magnetic data of 1, 3, and 4 exhibited a very weak antiferromagnetic coupling (J = −0.72 cm−1 for 1, −0.65 cm−1 for 3 and 4) between two metal centers in the dinickel core.

Cationic Methallylnickel and (Meth)allylpalladium 2-Phosphinophenol Complexes: Synthesis, Structural Aspects, and Use in Oligomerization of Ethylene

Reactions of methallylnickel bromide with 2-R2PC6H4OH 1a,b (R = Ph, cHex) and AgSbF6 furnish methallylnickel phosphinophenol hexafluoroantimonates 2a,b, which are not very stable and decay in solution at room temperature within an hour (2a) or days (2b) to tetranuclear nickel complexes 3a,b. The related cationic allylpalladium complex 4a is more stable. A crystal structure analysis gives evidence of the monomeric nature, the typical η3-coordination of the allyl group, and the coordination of the phenolic hydroxyl group to palladium. In solution the OH group is uncoordinated and underlines the hemilabile character of the phosphinophenol ligands. The allylpalladium phosphinophenol tetrafluoroborate 5a, stable as a solid, slowly decomposes in CDCl3 solution to give a dinuclear complex 6a and in THF/water as the solvent the palladium bis(phosphinophenolate) 7a. Methallylpalladium phosphinophenol acetates 8a,b, existing as phosphinophenolate acetic acid conjugates, are uncommonly stable and lose the acid on he...

Nickel Complexes of Carboxylate-Containing Polydentate Ligands as Models for the Active Site of Urease

Two new carboxylate-containing polydentate ligands have been synthesized, the symmetric ligand 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-aminomethyl)-4-methylphenol (ICIMP). The ligands have been used to prepare model complexes for the active site of the dinuclear nickel enzyme urease, viz. [Ni(2)(BCIMP)Ac(2)](-) (6), [Ni(2)(BCIMP)(Ph(2)Ac)(2)](-) (7), [Ni(2)(ICIMP)(Ph(2)Ac)(2)] (14), [Ni(4)(ICIMP)(2)(Ph(2)Ac)(2)][ClO(4)](2) (15), [Ni(4)(ICIMP)(2)(Ph(2)Ac)(2)(DMF)(2)][ClO(4)](2) (16), and [Ni(4)(ICIMP)(2)(Ph(2)Ac)(2)(urea)(H(2)O)][ClO(4)](2) (17), where the latter complex contains urea coordinated in a unidentate fashion through the carbonyl oxygen. The N(2)O-N(2)O(2) donor set of ICIMP provides a good framework for the preparation of urease models, but in some cases tetranuclear nickel complexes are formed due to coordination of the carboxylate moiety of one dinickel-ICIMP unit to one or both of the nickels of a second Ni(2) unit. Reactivity and kinetics studies of 7 and 15 show that these model complexes catalyze hydrolysis of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) at basic pH. In this assay, complexes based on the asymmetric ligand ICIMP exhibit a significantly faster rate of hydrolysis than the corresponding BCIMP complexes. Magnetic measurements indicate that there are weak antiferromagnetic interactions between the nickel ions in complex 16.