Binuclear Nickel Complexes Research Articles

Synthesis, Structure, and Biological Activity of Binuclear Mixed-Ligand Complexes of Nickel(II) Benzoylhydrazone 2-(N-Tosylamino)Benzaldehyde

Synthesis, Structure, and Biological Activity of Binuclear Mixed-Ligand Complexes of Nickel(II) Benzoylhydrazone 2-(N-Tosylamino)Benzaldehyde

The comparison of mononuclear and binuclear nickel complexes in their synthesis and catalytic performance of styrene oxidation

The synthesis, characterization, and catalytic activity of four new nickel hydrazone complexes: [NiL2] (1), [Ni(HL)2]·2ClO4·3H2O (2), [Ni2L2(NCS)2(H2O)2]·2H2O (3) and [Ni2L2(NCNCN)2(CH3OH)2] (4) were reported here. HL was obtained by mixing 2-acetylpyridine, 2-aminobenzohydrazine, and methanol together. Complexes 1–4 were synthesized using HL and nickel perchlorate as the main raw materials, methanol as the solvent, and different auxiliary materials. The four complexes were characterized by FT-IR, UV–Vis, and 1H NMR, and their structures were further confirmed by X-ray single crystal diffraction. The impact of the four complexes on styrene oxidation was assessed by employing H2O2 as the oxidant. Investigations revealed that each complex demonstrated effective catalytic functions. Catalytic activity parameters, such as the ratio of substrate to oxidant, temperature, reaction time, catalyst dosage, solvent dosage, and solvent properties, as well as the effect of acid and base additives, were optimized to obtain better conversion of styrene. In particular, the different catalytic performance between mononuclear and binuclear nickel complexes was compared, and a possible mechanism was proposed.

A new binuclear Ni(II) complex, an effective A3-coupling catalyst in solvent-free condition

A newly binuclear nickel(II) complex, [Ni2(en)4(ox)](ClO4)2 (1) (where en = ethylenediamine, and ox = oxalate), has been isolated from a reaction of NiCl2·6H2O, ethylenediamine, ammonium oxalate and sodium perchlorate in water and its crystal structure has been determined by X-ray crystallography and infra-red techniques. Compound 1 was successfully employed to promote the one-pot reaction of aldehydes, amines and acetylenes for the construction of corresponding propargylamines under solvent-free media with fine yields. Further studies reveal this catalytic system can be refreshed and used again in five runs.

The investigation of two bis(phenoxo)-acetate-bridged binuclear nickel(II) complexes driven by different alcohol solvents

Two solvent-induced bis(phenoxo)-acetate-bridged binuclear Ni(II) complexes, [Ni2(L)(µ-OAc)(CH3OH)] (1) and [Ni2(L)(µ-OAc)(H2O)] (2), were synthesized with a bis(salamo)-like ligand H3L and Ni(OAc)2·4H2O in two different alcohol solvents (methanol and ethanol). Complexes 1 and 2 were described by elemental analyses, single crystal X-ray diffraction, IR spectra, UV–vis spectra and fluorescence spectra. Complexes 1 and 2 have analogous crystal structures, but the non-covalent interactions are distinct. The one-dimensional chain of 1 is formed by π–π interactions, and the three-dimensional supramolecular network structure of 2 is formed by intermolecular hydrogen bonding interactions. In addition, fluorescence experiments indicated that the fluorescence of 1 and 2 undergoe a significant quenching compared to H3L. Intermolecular forces were investigated using Hirshfeld surface analysis. DFT calculations showed that 1 and 2 have high chemical reactivity and low kinetic stability.

Structure and stability of nickel(II) complexes with cryptand[2.2.2

The values of the stability constants of the mononuclear, protonated and binuclear complexes of nickel(II) with cryptand [2.2.2] were determined using potentiometric titration at ionic strength value µ→0 and temperature of 298 K. The structure and the most important geometric characteristics of Ni2 + cryptates were optimized via quantum chemical calculations performed in vacuo .

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.

Lantern-type dinickel complexes: An exploration of possibilities for nickel-nickel bonding with bridging bidentate ligands.

Many binuclear nickel complexes have NiNi distances suggesting NiNi covalent bonds, including lantern-type complexes with bridging bidentate ligands. This DFT study treats tetragonal, trigonal, and digonal lantern-type complexes with the formamidinate, guanidinate, and formate ligands, besides some others. Formal bond orders (ranging from zero to two) are assigned to all the NiNi bonds on the basis of MO occupancy considerations. A VB-based electron counting approach assigns plausible resonance structures to the dinickel cores. Model tetragonal complexes with the dimethylformamidinate and the dithioformate ligands have singlet ground states whose non-covalently bonded NiNi distances are close to those in their experimentally known counterparts. Trigonal dinickel complexes are unknown, but are predicted to have quartet ground states with NiNi bonds of order 0.5. The model digonal complexes are predicted to have triplet ground states, but the predicted NiNi bond lengths are longer than those found in their experimentally known counterparts. This could owe to inadequate treatment of electron correlation by DFT in these short NiNi bonds with their multiconfigurational character. All the NiNi bond distances here are categorized into ranges according to the NiNi bond orders of 0, 0.5, 1, 1.5, and 2, no NiNi bonds of order higher than two being identified. The NiNi bonds of given order in these lantern-type complexes are consistently shorter than the corresponding NiNi bonds in dinickel complexes having carbonyl ligands, attributable to the metalmetal bond lengthening effect of CO ligands.

Structural, theoretical and biological activity of mono and binuclear nickel(II) complexes with symmetrical and asymmetrical 4,6-diacetylresorcinol-dithiocarbazate ligands

The present work reports the synthesis and a structural study of two novel dithiocarbazate, the 4,6-diacetylresorcinol-S-benzyldithiocarbazate (H3L1) and the 4,6-diacetylresorcinol-bis(S-benzyldithiocarbazate) (H4L2), and their Ni(II) complexes, [Ni(HL1)(Py)] (1) and [Ni2(L2)(PPh3)2] (2). Single crystal X-ray analyzes reveal mono and binuclear complexes and the metal centers with distorted square planar geometry. The analyses of the Hirshfeld surface and fingerprints plots revealed intermolecular contacts attributed to the H···H and C···H/H···C bonds. The Density Functional Theory (DFT), with the B3LYP functional and 6–311-G(d,p)/LanL2DZ basis sets, was employed to optimize the geometries of synthesized compounds. From the resulting geometries, the highest occupied and lowest unoccupied molecular orbital maps (HOMO-LUMO), orbital energy gap, electron localization function (ELF), electron density, natural bond orbital (NBO) analysis, and complexation of the ligands with Ni(II) were calculated supporting the experimental data. The ESI (+)-MS/MS data indicated the presence in solution of the characteristic fragmentation with the [H3L1]+ and [H4L2]+ molecular ions for the ligands. The pharmacological potential of the dithiocarbazate ligands and their Ni(II) complexes were evaluated in vitro against MDA-MB-231 human breast cancer cells. A remarkable cytotoxic activity was observed, more evident for free ligands than complexes at low concentrations; however, this latter showed a better dose–response pattern, being more attractive in terms of pharmacokinetics and therapeutic window.

The non-templating synthesis of macro-cyclic Schiff base ligands containing pyrrole and homopiperazine and their binuclear nickel(II), cobalt(II) and mononuclear platinum(II) complexes: X-ray single crystal and anticancer studies

A new dialdehyde N, N'-bis(5-formylpyrrol-2-ylmethyl) homopiperazine (A) was synthesized by the Mannich reaction of pyrrole 2-carbaldehyde, formaldehyde and homopiperazine in the presence of hydrochloric acid. From the direct reaction of A with 1,3-diaminopropane or 1,4- diaminobutane two new macrocyclic Schiff base ligands were obtained, L1 and L2, respectively. The reaction of these ligands with Ni(II), Co(II) and Pt(II) metal ions results in formation of the relevant macrocyclic Schiff base complexes. Compounds were characterized by FT-IR, elemental analysis, mass spectrometry, UV-Vis and, in the case of the ligands, by 1H and 13C-NMR. The crystal structure of the complex [Ni2L2(CH3O)]ClO4 (4) showed a binuclear macro-cyclic structure, with each Ni coordinated by three nitrogen atoms from the ligand and by a methoxide bridging the two metal centers. The cytotoxic activities of these compounds indicated that the ligands, and some of the complexes, have high anti-proliferative effect towards A549 and HeLa cells, but not HT29 cells. Pt complex with L1 and L2 displayed stronger anti-proliferative activity toward HeLa (IC50 = 11 µM for both of them and A549 IC50 = 7 µM and 8 µM, respectively) relative to L1 and L2. In addition, the cytotoxic effects of the compounds were assayed in rat fibroblast cells as a model of the normal cell, however none of them showed any significant cytotoxic effects. Thereby upholding the potential of these compounds for further development as chemotherapeutic agents.

Photohalogen elimination chemistry in low-valent binuclear nickel complexes

The photogeneration of X2 is the key to achieving an efficient HX-splitting photocycle, as it is more thermodynamically and kinetically challenging than its H2 half reaction counterpart. Here we report a strategy that enables Cl2 photoelimination from low-valent binuclear d9–d9 and d9–d10 Ni complexes. We demonstrate the importance a of metal–metal bond interaction for M–X bond photoactivation with a combination of TD-DFT computations together with spectroscopy and photocrystallography, exemplifying a design principle for future developments of 3d metal complexes for HX photocatalysis.

One new hexatungstate-based binuclear nickel(II) complex with high selectivity adsorption for organic dyes

A new hexatungstate compound, [Ni2(L)3]2[W6O19]·2H2O (1) (HL = 2-acetylpyrazine-N(4)-methyl thiosemicarbazone) has been synthesized and characterized by elemental analyses, infrared (IR) spectroscopy, thermal gravimetric analysis (TGA), powder X-ray diffraction (PXRD), single-crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and UV–Vis spectra. A 3D supramolecular structure of 1 is formed by hydrogen bonding, which exhibits a highly selective adsorption for methylene blue (MB), gentian violet (GV) and fuchsin basic (FB) organic dyes with the efficiencies of 99%, 94% and 94%, respectively. Additionally, the adsorption kinetics demonstrates that the MB removal corresponds to the pseudo-second-order model. The recyclability experiments illustrated that 1 could be reused at least five cycles, revealing a potential ability in the disposal to dye wastewater.

High Enzyme Activity of a Binuclear Nickel Complex Formed with the Binding Loops of the NiSOD Enzyme**

Detailed equilibrium, spectroscopic and superoxide dismutase (SOD) activity studies are reported on a nickel complex formed with a new metallopeptide bearing two nickel binding loops of NiSOD. The metallopeptide exhibits unique nickel binding ability and the binuclear complex is a major species with 2×(NH2,Namide,S−,S−) donor set even in an equimolar solution of the metal ion and the ligand. Nickel(III) species were generated by oxidizing the NiII complexes with KO2 and the coordination modes were identified by EPR spectroscopy. The binuclear complex formed with the binding motifs exhibits superior SOD activity, in this respect it is an excellent model of the native NiSOD enzyme. A detailed kinetic model is postulated that incorporates spontaneous decomposition of the superoxide ion, the dismutation cycle and fast redox degradation of the binuclear complex. The latter process leads to the elimination of the SOD activity. A unique feature of this system is that the NiIII form of the catalyst rapidly accumulates in the dismutation cycle and simultaneously the NiII form becomes a minor species.

Methylene‐bridged bis(8‐arylimino)‐5,6,7‐trihydro‐quinolylinickel precatalysts for ethylene polymerization

AbstractA series of binuclear nickel complexes bearing N‐(5,6,7‐trihydroquinolin‐8‐ylidene)amino CH(C6H4‐4‐R2){4‐C6H2‐2,6‐R12N‐(C5H3NC4H6)}2 [R1 = Me, R2 = OH L1, R1 = Et, R2 = OH L2, R1 = Me, R2 = H L3, R1 = Me, R2 = OCH3L4] has been synthesized and characterized. In the presence of either methylaluminoxane (MAO) or Et2AlCl, all nickel complexes exhibited high activities up to 3.33 × 106 g (PE)·mol−1(Ni)·hr−1 toward ethylene polymerization, producing high branched polyethylenes (PEs). The aluminum cocatalysts have significantly affected the properties of resultant PE; with MAO as the cocatalyst, the resultant PE shows higher molecular weight and possesses only one Tm value, meanwhile Et2AlCl as the cocatalyst, the obtained PE indicates lower molecular weight and two melting points. The microstructures of those PEs determined by their 13C NMR spectra illustrate the similar densities but different types of branches, in which the PE obtained with Et2AlCl shows high methyl branch selectivity (>80%), and the PE produced by MAO has 50% methyl and another half of longer branches. The branched PEs are consistent to the chain migration happened in the ethylene polymerization.

A chiral binuclear nickel(II) complex with Schiff base ligand: synthesis, crystal structure, DNA/BSA binding interactions and SOD activity

A chiral binuclear Ni(II) complex [Ni2(o-van-ala)2(phen)2] (o-van-ala = a Schiff base derived from o-vanillin and l-alanine, phen = 1,10-phenanthroline) has been synthesized and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray diffraction result showed that the Ni(II) complex contains two nickel centers, which are further bridged and coordinated by two o-van-ala Schiff base and two phen ligands in a cis-conformation. Each nickel atom is six-coordinated in a distorted NiN3O3 octahedral geometry. The interaction of the Ni(II) complex with calf thymus DNA (CT-DNA) has been investigated by spectroscopic methods. Based on results obtained, an intercalative binding mode has been proposed. In addition, the interaction between the Ni(II) complex and bovine serum albumin (BSA) has also been studied by various spectroscopic techniques. Results indicated that the Ni(II) complex can quench the intrinsic fluorescence of BSA in a static quenching process. The binding constant (Kb) and the number of binding sites (n) were calculated to be 2.92 × 106 M−1 and 1.21, respectively. Site-selective competitive binding experiment indicated that the binding site of the Ni(II) complex locates in site I in sub-domains IIA of BSA. The Ni(II) complex also displayed a significant superoxide anion scavenging activity.

Binuclear Nickel(II) Complex Containing 6-Methyl-2,2'-bipyridine and Chloride Ligands: Synthesis, Characterization, Thermal Analyses, and Crystal Structure Determination

A new binuclear complex of [{NiCl(6-mbipy)}2(μ-Cl)2] (1) was prepared from the reaction of NiCl2.6H2O and 6-methyl-2,2'-bipyridine (6-mbipy) in a mixture of methanol and acetonitrile. Suitable crystals of 1 for X-ray diffraction measurement were obtained by slow evaporation of the resulted green solution at room temperature. Complex 1 was characterized by spectral methods (IR, UV–Vis, and luminescence), elemental analysis (CHN), and single-crystal X-ray diffraction. The structure of 1 is centrosymmetric binuclear complex and each Ni(II) cation is five-coordinated in a slightly distorted square-pyramidal configuration. In this binuclear complex, the Ni…Ni distance is 3.533(1)A. Furthermore, the luminescence emission of the title complex was blue-shifted and is stronger than that of free 6-methyl-2,2'-bipyridine ligand. Thermal stabilities of this complex was also studied by thermogravimetric analysis.

Binuclear iminopyridine-bridged 3d late transition metal complexes with o-semiquinones

Four novel binuclear high spin manganese(II), iron(II), cobalt(II) and nickel(II) complexes containing 1,2-bis(pyridin-2-ylmethylene)-para-phenylenediamine as a bridging ligand have been synthesized and investigated. Molecular structures of manganese and cobalt complexes were established by single crystal X-ray structural analysis. For all the complexes the magnetic susceptibility measurements have been performed. According to the obtained magnetic data the energies of intramolecular magnetic exchange interactions strongly depend on the electron structure of metal ion. In addition, all the obtained complexes demonstrate very weak antiferromagnetic metal-metal interaction.

Symmetric and Asymmetric Binuclear α-Diimine Nickel(II) Complexes for Ethylene Polymerization

A series of symmetric and asymmetric binuclear α-diimine nickel(II) complexes toward ethylene polymerization were successfully synthesized and characterized by 1HNMR. All the catalysts were typically activated with MAO and displayed good activity at room temperature under 1atm ethylene pressure. The symmetric catalyst containing isopropyl on ligand-activated with 500 equiv MAO produced high molecular weight polyethylene with a PDI=1.75, while the symmetric catalyst containing methyl on ligand produced relatively low molecular weight polyethylene with a PDI=1.74. By contrast, the molecular weight, branching density of resultant polymer produced by asymmetric catalyst decrease roughly somewhere between that of polymers prepared by two symmetric catalysts.

Synthesis, structural and DFT analysis of a binuclear nickel(II) complex with the 1,4-bis[2-[2-(diphenylphosphino)benzylidene]]phthalazinylhydrazone ligand

In this work we present the synthesis, and experimental and theoretical analysis of a binuclear nickel(II) complex coordinated to a new phthalazine dihydrazone-based ligand. Single-crystal X-ray diffraction analysis of the metal complex shows that the coordination geometry around each nickel(II) atom is distorted octahedral. DFT calculations predict that the magnetic exchange coupling constant of the binuclear nickel(II) complex is predominantly anti-ferromagnetic.

Solution and solid behavior of mono and binuclear zinc(ii) and nickel(ii) complexes with dithiocarbazates: X-ray analysis, mass spectrometry and cytotoxicity against cancer cell lines

We report the synthesis and characterization of metal complexes with dithiocarbazates and the cytotoxicity against the breast cancer line MDA-MB-231.

Model Complexes for the Nip Site of Acetyl Coenzyme A Synthase/Carbon Monoxide (CO) Dehydrogenase: Structure, Electrochemistry, and CO Reactivity.

Aliphatic thiolato-S-bridged tri- and binuclear nickel(II) complexes have been synthesized and characterized as models for the Nip site of the A cluster of acetyl coenzyme A synthase (ACS)/carbon monooxide (CO) dehydrogenase. Reaction of the in situ formed N2Sthiol donor ligands with [Ni(H2O)6](ClO4)2 afforded the trinuclear complexes [Ni{(LMe(S))2Ni}2](ClO4)2·CH3CN (1·CH3CN) and [Ni{(LBr(S))2Ni}2](ClO4)2·5H2O (2·5H2O) following self-assembly. Complexes 1 and 2 react with [Ni(dppe)Cl2] and dppe [dppe = 1,2-bis(diphenylphosphino)ethane] to afford the binuclear [Ni(dppe)Ni(LMe(S))2](ClO4)2·2H2O (3·2H2O) and [Ni(dppe)Ni(LBr(S))2](ClO4)2·0.75O(C2H5)2 [4·0.75O(C2H5)2], respectively. The X-ray crystal structures of 1-4 revealed a central NiIIS4 moiety in 1 and 2 and a NiIIP2S2 moiety in 3 and 4; both moieties have a square-planar environment around Ni and may mimic the properties of the Nip site of ACS. The electrochemical reduction of both terminal NiII ions of 1 and 2 occurs simultaneously, which is further confirmed by the isolation of [Ni{(LMe(S))2Ni(NO)}2](ClO4)2 (5) and [Ni{(LBr(S))2Ni(NO)}2](ClO4)2 (6) following reductive nitrosylation of 1 and 2. Complexes 5 and 6 exhibit νNO at 1773 and 1789 cm-1, respectively. In the presence of O2, both 5 and 6 transform to nitrite-bound monomers [(LMe(S-S))Ni(NO2)](ClO4) (7) and [(LBr(S-S))Ni(NO2)](ClO4)2 (8). The nature of the ligand modification is evident from the X-ray crystal structure of 7. To understand the origin of multiple reductive responses of 1-4, complex [(LMe(SMe))2Ni](ClO4)2 (9) is considered. The central NiS4 part of 1 is labile like the Nip site of ACS and can be replaced by phenanthroline. The treatment of CO to reduce 3 generates a 3red-(CO)2 species, as confirmed by Fourier transform infrared (νCO = 1997 and 2068 cm-1) and electron paramagnetic resonance ( g1 = 2.18, g2 = 2.13, g3 = 1.95, and AP = 30-80 G) spectroscopy. The CO binding to NiI of 3red is relevant to the ACS activity.