Binuclear Nickel Complexes Research Articles

Computational Study on the Structural and Electronic Properties of Multi-Nuclear Palladium and Nickel Silyl Complexes via DFT and QTAIM Approaches

In this research, we have concentrated on the survey of ability of density functional methods and also modern semi-empirical approaches to reproduce the crystal structure of a binuclear silyl nickel complex and a trinuclear palladium silyl complex. In the structural analysis of the aforesaid nickel and palladium complexes, we have also interested to investigate the possibility of Si-Si bond formation between SiH2 and μ-SiH moieties from the structural and electronic viewpoints. Comparison of our calculated structural parameters of aforementioned complexes with the available X-ray crystallographical data reveals that both functionals (B3LYP and M062X) can well reproduce X-ray structure of the complex with a near accuracy while the PM6-D2 semi-empirical calculated values are not in a reliable agreement with the crystallographical data. In the next step, we assessed the nature of interactions between palladium and nickel metal ions with silyl ligands via Quantum Theory of Atoms in Molecule (QTAIM) computations. Furthermore, we have analyzed the possibility of Si-Si bond formation in the aforementioned complexes by means of topological electronic indices. Strictly speaking, QTAIM calculations have been performed to explore the electronic density, its laplacian and electronic energy density at some key bond critical points to interpret the structural features of aforesaid complexes from the electronic point of view.

Exceptional Behavior of Ni2O2 Species Revealed by ESI-MS and MS/MS Studies in Solution. Application of Superatomic Core To Facilitate New Chemical Transformations

Acetonitrile solutions of nickel(II) acetylacetonate, which is ubiquitously used in different fields of organometallic chemistry and catalysis, were investigated by means of electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The detected Ni2(acac)3+ ion with the binuclear Ni2O2 core underwent a wide range of reactions after collision-induced dissociation, leading to a variety of products. Activation of C–H, C–C, and C–O bonds was observed involving the binuclear nickel complex. In sharp contrast, similar ions involving mononuclear and trinuclear nickel species did not show such exceptional behavior. The findings may open a fascinating direction in the field of superatoms to develop new chemical transformations for organometallic chemistry and catalysis. The higher relative stability of binuclear species was also observed in ESI mass spectra of copper and vanadyl complexes with acetylacetonate ligands, Cu2(acac)3+ and (VO)2(acac)3+. An important point concerns the purity of the studied solutions, since even a trace level of contaminants has drastically diminished the outcome of the mechanistic studies.

Synthesis, characterization and structural studies of binuclear nickel(II) complexes derived from dihydroxybenzaldehyde thiosemicarbazones, bridged by 1,2-bis(diphenylphosphino)ethane

The work described in this paper involves the synthesis and structural characterization of Ni(II) complexes derived from dihydroxybenzaldehyde thiosemicarbazones (H3L1, H3L2, H3L3, H3L4) and 1,2-bis(diphenylphosphino)ethane (dppe). Ligands and their Ni(II) complexes were characterized by elemental analysis, IR, UV–Vis, (1H, 13C, 31P) NMR, as well as magnetic moment and X-ray structure analysis. The results so obtained suggest that the thiosemicarbazone ligands behave as a tridentate ligand which were coordinated with Ni(II) ion through O, N and S atoms. Furthermore, the dppe ligand was coordinated with Ni(II) ion through the P atom. It is concluded that all Ni(II) complexes have a Square-planar geometry.

Binuclear copper(ii) and nickel(ii) complexes based on N,N′-bis(3-formyl-5-tert-butylsalicylidene)-1,3-diaminopropan-2-ol: physicochemical and theoretical study

Binuclear CuII and NiII complexes with exogenous acetate and pyrazolate bridges were synthesized and studied. It was shown that the μ2-coordination of the DMSO molecule in an acetate-bridged CuII complex leads to the inversion of the sign of the exchange interaction parameter. Quantum chemical calculations of the geometry of the complexes and the magnetic exchange parameters showed that the role of the DMSO molecule is to stabilize the “distorted” conformation of metallocycles.

Synthesis and application of binuclear α-diimine nickel/palladium catalysts with a conjugated backbone

A series of binuclear nickel/palladium catalysts C4-C7 with conjugated α-diimine ligands were designed, prepared and fully characterized. The binuclear nickel complexes C6 and C7 were activated by modified methylalumoxanes (MMAO) to generate highly active ethylene polymerization catalysts with activities up to 1050 kg [mol (Ni) h](-1). The activity of C7 is twice that of the mononuclear analogue under the same conditions. The effects of the catalyst structure, cocatalyst ratio, polymerization time, solvent and feeding monomer on the catalytic activities, molecular weight and branching structures of the resulting polymers were evaluated. The binuclear palladium complexes C4-C5 produced polyethylene with two separate peaks in GPC curves in ethylene polymerization. In contrast, the mononuclear analogue C3 produces polyethylene with a unimodal GPC curve. Probably, two active species are generated in the binuclear palladium catalyst system and are responsible for the bimodal feature of the GPC curves. The performance of the binuclear palladium complexes in ethylene/methyl acrylate copolymerization was also investigated.

Synthesis, Characterization and Ethylene Oligomerization Studies of Nickel Complexes Bearing Novel Bis-α-diimine Ligands

Sterically modulated, diazine bridged bis-α-diimine Ni(II) complexes have been synthesized to provide a versatile set of catalytic systems for ethylene oligomerization in combination with methyl aluminoxane (MAO) as cocatalyst. All the dinickel catalysts efficiently oligomerize ethylene to produce C4–C20 fractions at activities of up to 1,123 kg-oligomer mol-Ni−1 bar−1 h−1 at 30 °C with Al(MAO)/Ni ratio at 300. The change in potential of metal center induced by substituents, as evidenced by cyclic voltammetric measurements, influences the oligomerization activity. Complexes C1 and C3 produces traces of polyethylene at 30 °C, while at higher temperature all the complexes yielded oligomers only. A series of sterically modulated binuclear nickel(II) complexes of three novel bis-α-diimine ligands have been synthesized. The square planar dinickel(II) center complexes efficiently oligomerize ethylene to C4–C20 fractions showing high selectivity towards 1-butene as nearly as 75 % of the total C4 content .

Self-immobilizing binuclear neutral nickel catalyst for ethylene polymerization: Synthesis and catalytic studies

A allyl-substituted salicylaldimine proligand (Scheme 1, Compound 5) was prepared by a condensation reaction, which reacted with trans-[NiCl(Ph)(PPh3)2] to give a binuclear neutral nickel (II) complex [((4-Allyl-2,6-iPr2C6H2) NCH)C6H3ONi(PPh3)Ph]2 (Scheme 1, Complex 6). The structure of the complex was characterized by 1H NMR, 13C NMR and elemental analysis. This novel complex bearing allyl groups can be used as a self-immobilizing catalyst for the polymerization of ethylene and does not need a cocatalyst for their catalytic performance. The self-immobilizing catalytic systems not only possess high activity (up to 5.23×105g of PE/(mol of Nih)) but also can produce high-molecular-weight polyethylenes (Mw=(0.42–0.71)×106) with relatively broad molecular weight distributions (MWD=2.83–3.11). According to the 13C NMR analyses, the resultant polyethylenes contain a few branched chains mainly consisting of methyl branches.

Synthesis, characterization, catalytic, and biological studies of macrobicyclic binuclear nickel(II) complexes of 1,8-difunctionalized cyclam derivatives

New Schiff base binuclear nickel(II) complexes of N-substituted cyclam derivatives have been prepared by template condensation of 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. The ligand possesses two coordination sites, an N4O2 amine compartment and N3O2/N4O2 imine compartment. The structural features of the complexes have been confirmed by elemental analysis, IR, UV–Vis, and mass spectra. From the data, octahedral geometry around the two nickels has been suggested. The electrochemical behavior of the complexes show two irreversible one-electron reduction process in the cathodic region and show two irreversible one-electron oxidation process at the anode. Hydrolysis of 4-nitrophenylphosphate using the complexes as catalysts have been carried out. Antimicrobial screening data show good results. The binding of the complexes to calf thymus DNA (CT DNA) has been investigated with absorption and emission spectroscopy. Ni2L1 displays significant cleavage of circular plasmid pBR322 DNA to linear form. Spectral, electrochemical, and catalytic studies support distortion of the nickel geometry that arises as the macrocyclic ring size increases.

Flexible Mono‐ and Bis‐tetraazamacrocyclic Complexes of Copper and Nickel Stabilizing Different Oxidation States

AbstractThe synthesis and structural properties of new mono‐ and bis‐macrocyclic cyclidene complexes of copper(II) andnickel(II) are presented. The compounds with aliphatic ligands are flexible enough to stabilize metal centers in the three oxidation states +1, +2, and +3. All the electron‐transfer processes in the 16‐membered mono‐ and binuclear macrocyclic complexes of copper(II) and nickel(II) were fast and reversible. Two polymorphic forms of the 16‐membered mononuclear complex of nickel(II) were isolated in the solid state and characterized. The 16‐membered macrocyclic complexes show both U‐ and Z‐shape conformations. The deviation of the macrocyclic ligand from planarity affects the electrochemical properties of the complexes and leads to stabilization of different oxidation states of the Cu and Ni metal centers. Substitution of the exocyclic nitrogen atoms with a second alkyl group increases the deviation from planarity and induces rotation of the functional groups at the meso position relative to the macrocyclic ring. In the bis‐macrocyclic complexes, the electron‐donating properties are improved and the formal potential of the metal(II)/metal(III) system is less positive with increasing linker length between the macrocyclic units. The acceptor properties of the metal(II) complexes are weaker, the formal potential of the metal(II)/metal(I) couple being shifted to more negative values.

Metal Complexes of Bridging Neutral Radical Ligands: pymDTDA and pymDSDA

Metal complexes of the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl (pymDTDA) neutral radical ligand and its selenium analogue (pymDSDA) are presented. The following series of metal ions has been studied using M(hfac)(2) as the coordination fragment of choice (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato): Mn(II), Co(II), Ni(II), and Zn(II). The binuclear cobalt and nickel complexes of pymDTDA both exhibit ferromagnetic (FM) coupling between the unpaired electrons on the ligand and the metal ion, while the binuclear zinc complex of pymDTDA is presented as a comparative example incorporating a diamagnetic metal ion. The binuclear manganese complex of pymDTDA, reported in a preliminary communication, is compared to the pymDSDA analogue, and new insight into the magnetic behavior reveals that intermolecular magnetic coupling, mediated by chalcogen-oxygen contacts, gives rise to a significant increase in the χT product at low temperature. Surprisingly, the binuclear nickel complex of pymDSDA forms dimers in the solid state, as do the mononuclear complexes of cobalt and nickel with pymDTDA. In addition, mixed mononuclear/binuclear complexes of Mn- and Zn(pymDTDA) have been identified.

DNA binding, DNA hydrolase and phosphatase like activity of new polyaza macrobicyclic binuclear copper(II), nickel(II) and zinc(II) complexes

A new class of mono, polyaza macrobicyclic binuclear copper(II), nickel(II) and zinc(II) complexes 1–6 are synthesized and characterized. The redox, phosphate hydrolysis, DNA binding and cleavage properties of complexes 1–6 are studied. The mononuclear Cu(II)-complex 1 is structurally characterized by single-crystal X-ray diffraction study. They exhibit a quasi-reversible cyclic voltammetric response near −0.65V versus Ag/AgCl in CH3CN-0.1M TBAP assignable to the M2II/M2I redox couple. The initial rate values for the hydrolysis of 4-nitrophenylphosphate to 4-nitrophenolate by the complexes 1–6 are in the range from 1.82×10−6 to 1.25×10−4s−1. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range from 1.1 to 9.5×105M−1. The binding site size and viscosity data suggest the DNA groove binding of the complexes. The complexes display significant hydrolytic cleavage of supercoiled pBR322 DNA at pH 7.2 and 37°C. The hydrolytic cleavage mechanism is further supported by free radical quenching and T4 ligase ligation results. The pseudo-Michaelis–Menten kinetic parameters kcat=2.13±0.3h−1 and KM=5.12×10−5M for macrobicyclic binuclear zinc(II) complex (6) were obtained.

A new bis(azine) tetradentate ligand and its transition metal complexes: Synthesis, characterisation, and extraction properties

AbstractA new bis(bidentate) azine ligand was prepared by linking (1Z,1′Z)-1,1′-{butane-1,4-diylbis[oxybenzene-4,1-diyl(1Z)ethyl-1-ylidene]}dihydrazine to salicylaldehyde. Two kinds of binuclear copper(II) and nickel(II) complexes with different stoichiometries were prepared. Reaction of bis(azine) ligand with Cu(II) and Ni(II) acetate at a 1: 1 mole ratio gave double-stranded binuclear bis(azine) complexes with stoichiometry [M(L)(H2O)2]2 containing [M(II)N2O2] centres while at a 2: 1 mole ratio, reaction of Cu(II) and Ni(II) chloride with bis(azine) resulted in dinuclear metal complexes with the general stoichiometry [M2(L)Cl2(H2O)2]. Structures of the bis(azine) ligand and its complexes were identified by elemental analysis, IR and UV-VIS spectra, magnetic susceptibility measurements, TGA, and powder XRD. Extraction properties of the bis(azine) ligand towards some transition metal cations and dichromate anions were also reported. It was found that the bis(azine) ligand does not extract cations but it has high extraction ability towards dichromate anions.

X-ray photoelectron spectroscopy study of electron and spatial structure of mono- and binuclear Ni(II) carboxylate complexes with nitrogen-containing ligands

Ni3 s, Ni3 p and Ni2 p X-ray photoelectron spectra of mono- and binuclear carboxylate complexes of nickel with various geometry of metal atoms environment are obtained. The spectra are calculated in an isolated ion approximation. The dependence of the spectral profiles and the structure of the charge-transfer satellites on the structure of the immediate environment of nickel atoms is established. The data obtained support the results of X-ray diffraction and magnetic studies.

Cyanato bridged binuclear nickel(II) and copper(II) complexes with pyridylpyrazole ligand: Synthesis, structure and magnetic properties

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)]2(PF6)2 (1) and copper(II) complex [Cu(L)(NCO)]2(PF6)2 (2), where L is N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N4-coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2. The variable temperature magnetic susceptibility data, measured from 2 to 300K, show weak antiferromagnetic interaction with J value −6.2(1)cm−1 for complex 1, whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1)cm−1.

New Dinuclear Nickel(II) Complexes: Synthesis, Structure, Electrochemical, and Magnetic Properties

The reaction of [NiBr(2)(bpy)(2)] (bpy = 2,2'-bipyridine) with organic phosphinic acids ArP(O)(OH)H [Ar = Ph, 2,4,6-trimethylphenyl (Mes), 9-anthryl (Ant)] leads to the formation of binuclear nickel(II) complexes with bridging ArP(H)O(2)(-) ligands. Crystal structures of the binuclear complexes [Ni(2)(μ-O(2)P(H)Ar)(2)(bpy)(4)]Br(2) (Ar = Ph, Mes, Ant) have been determined. In each structure, the metal ions have distorted octahedral coordination and are doubly bridged by two arylphosphinato ligands. Magnetic susceptibility measurements have shown that these complexes display strong antiferromagnetic coupling between the two nickel atoms at low temperatures, apparently similar to binuclear nickel(II) complexes with bridging carboxylato ligands. Cyclic voltammetry and in situ EPR spectroelectrochemistry show that these complexes can be electrochemically reduced and oxidized with the formation of Ni(I),Ni(0)/Ni(III) derivatives.

Electrochemical, catalytic and antimicrobial activity of N-functionalized tetraazamacrocyclic binuclear nickel(II) complexes

The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d–d transition in the range of 550–1055 nm due to 3A 2g → 3T 2g(F), 3A 2g → 3T 1g(F) and 3A 2g → 3T 1g(P). These spin allowed electronic transitions are characteristic of an octahedral Ni 2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the complexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85 × 10 −3 to 9.14 × 10 −3 min −1. All the complexes were screened for antimicrobial activity.

Trifluorophosphine as a Bridging Ligand in Homoleptic Binuclear Nickel Complexes†

The stable tetrahedral derivative Ni(PF(3))(4) is reported to generate binuclear Ni(2)(PF(3))(n) ions in its mass spectrum emerging from ion-molecule reactions. Theoretical studies on such binuclear complexes indicate Ni(2)(PF(3))(7) to be energetically unfavorable with respect to decomposition into Ni(PF(3))(4) + Ni(PF(3))(3). However, viable rather unsymmetrical structures with two PF(3) bridges for Ni(2)(PF(3))(n) (n = 6, 5, 4) are reported here as well as a triply semibridged Ni(2)(PF(3))(5) structure. The nickel-nickel distances in these Ni(2)(PF(3))(n) derivatives suggest a formal double bond (2.51 A), a formal triple bond (2.26 A), and a formal double bond (2.34 A) for n = 6, 5, and 4, respectively. The mononuclear Ni(PF(3))(n) derivatives are predicted to have tetrahedral, trigonal planar, and bent (139 degrees ) structures for n = 4, 3, and 2, respectively.

Structural determinations and magnetic studies of two new binuclear complexes: azido-bridged Ni(II) dimer and di-(µ-hydroxo)-bridged Cr(III) dimer

Polydentate ligands 2-[(2-hydroxypropylimino)methyl] phenol (L) and pyridine-2,6-dicarboxylic acid (H2pda) have been used in the synthesis of binuclear transition metal complexes. A new doubly end-on azido-bridged binuclear nickel(II) complex with formula [(µ1,1-N3)2(L)2(N3)2] · H2O (1) and a bis-µ-hydroxo-bridged dinuclear chromium(III) complex with the formula [(OH)2(pda)2(H2O)2] (2) have been synthesized and characterized by single crystal X-ray diffraction and magnetic studies. Compound 1 displays intramolecular intermetallic ferromagnetic coupling with J = 28.32 cm−1 and D = −19.30 cm−1 based on the Hamiltonian Ĥ = −2JŜ 1 Ŝ 2 − D(+ ) − gβH(Ŝ 1 + Ŝ 2). Compound 2 displays intramolecular intermetallic antiferromagnetic coupling with J = −6.56 cm−1 based on the Hamiltonian Ĥ = −2JŜ 1 Ŝ 2 − j(Ŝ 1 Ŝ 2)2.

Binuclear cobalt(II), nickel(II), copper(II) and palladium(II) complexes of a new Schiff-base as ligand: Synthesis, structural characterization, and antibacterial activity

A binucleating new Schiff-base ligand with a phenylene spacer, afforded by the condensation of glycyl–glycine and o-phthalaldehyde has been served as an octadentate N 4O 4 ligand in designing some binuclear complexes of cobalt(II), nickel(II), copper(II), and palladium(II). The binding manner of the ligand to the metal and the composition and geometry of the metal complexes were examined by elemental analysis, conductivity measurements, magnetic moments, IR, 1H, 13C NMR, ESR and electronic spectroscopies, and TGA measurements. There are two different coordination/chelation environments present around two metal centers of each binuclear complex. The composition of the complexes in the coordination sphere was found to be [M 2(L)(H 2O) 4] (where M = Co(II) and Ni(II)) and [M 2(L)] (where M = Cu(II) and Pd(II)). In the case of Cu(II) complexes, ESR spectra provided further information to confirm the binuclear structure and the presence of magnetic interactions. All the above metal complexes have shown moderate to good antibacterial activity against Gram-positive and Gram-negative bacteria.

Synthesis of (2-hydroxo-5-chlorophenylaminoisonitrosoacetyl)phenyl ligands and their complexes: Spectral, thermal and solvent-extraction studies

Four different types of new ligands Ar(COC(NOH)R)n (Ar=biphenyl, n = 1 H2L 1 ; Ar=biphenyl, n = 2 H4L 2 ; Ar=diphenylmethane, n = 1 H2L 3 ; Ar=diphenylmethane, n = 2 H4L 4 ; R=2�amino�4�chlo� rophenol in all ligands) have been obtained from 1 equivalent of chloroketooximes Ar(COC(NOH)Cl) n (HL 1 -H2L 4 ) and 1 equivalent of 2�amino�4�chlorophenol (for H2L 1 and H2L 3 ) or 2 equivalent of 2�amino� 4�chlorophenol (for H4L 2 and H4L 4 ). (Mononuclear or binuclear cobalt(II), nickel(II), copper(II) and zinc(II) complexes were synthesized with these ligands.) These compounds have been characterized by ele� mental analyses, AAS, infrared spectra and magnetic susceptibility measurements. The ligands have been further characterized by 1 H NMR. The results suggest that the dinuclear complexes of H 2 L 1 and H 2 L 3 have a metal:ligand ratio of 1:2; the mononuclear complexes of H4L 2 and H4L 4 have a metal:ligand ratio of 1:1 and dinuclear complexes H4L 2 and H4L 4 have a metal:ligand ratio of 2:1. The binding properties of the ligands towards selected transition metal ions (Mn II , Co II , Ni II , Cu II , Zn II , Pb II , Cd II , Hg II ) have been established by extraction experiments. The ligands show strong binding ability towards mercury(II) ion. In addition, the thermal decomposition of some complexes is studied in nitrogen atmosphere.