Ni Dimer Research Articles

Adsorption of Hydrogen Molecules in Nickel Decorated Silicene

First-principles simulations based on density functional theory (DFT) have been used to study the structural, electronic and magnetic properties of pristine and Ni decorated silicene sheets. Generalized Gradient Approximation (GGA) based exchange correlation functionals are used under software package Quantum ESPRESSO (QE), 6.5 versions. We have reconstructed the optimized unit cell of silicene, which has a face centered cubic (fcc) structure with two silicon atoms having lattice parameters a = b = 3.8 Å. The distance between two nearest silicene monolayers is found to be 20.5 Å which is large enough to neglect the interlayer interactions between 4×4 supercells of silicene monolayers. The atoms in the prepared supercell are fully relaxed under Bloyden-Fletcher-Goldfarb-Shanno (BFGS) scheme prior to the self-consistent, band structure and density of state (DoS) calculations. The pristine silicene is semi-metallic in nature possessing a Dirac-cone as in graphene. The h-site adsorption is found to be the most stable adsorption site of nickel in silicene with the binding energy of 4.69 eV. The addition of nickel atom completely distorts the hexagonal structure of silicene destroying the Dirac cone and the system becomes slightly insulating from its semi-metallic nature. We then construct a 4×4 nickel dimer silicene which further destroys the hexagonal silicene structure with further opening of the band gap. The charge transfer analysis in the Ni decorated systems shows the charge transfers of 0.163e and 0.294e in Ni adatom silicene and Ni dimer silicene respectively showing that the nickel atoms are adsorbed by weak van der Waals forces in both of the systems. We then proceed to hydrogen molecule adsorption in these prepared 4×4 silicene systems: pristine, Ni adatom and Ni dimer silicene systems. The adsorption energy of hydrogen in the Ni adatom silicene is found to be the largest making it the most effective system for hydrogen storage.

Magnetic phase transition in dimer-based metal-organic frameworks through structural modulation

The flexibility of a structure is an important factor that affects the magnetic interactions, anisotropy, phase transitions, and domain structure of materials. It is essential to consider this factor for a thorough analysis of magnetic properties, as it enables researchers to design materials with specific magnetic characteristics for different purposes. In this work, experimental measurements were conducted to investigate the magnetic properties of DUT-8(Ni), composed of a Ni(II) dimer paddle wheel as the metal cluster and an organic linker. DUT-8(Ni) exhibits two distinct structures, one porous (open structure) and the other nonporous (closed structure), which have a significant impact on its magnetic properties. Our study focuses on the changes in its magnetic behavior due to these structural variations. The Ni(II) dimer's basic unit displays antiferromagnetic properties, and we observed interactions between intra- and inter-units in the 3D structure with the magnetic data we measured. To gain a deeper understanding, the magnetization of the open and closed structures is analyzed using a modified Langevin function.

Synthesis, crystal structure, fluorescence properties, and theoretical studies of a dinuclear Ni(II) complex derived from a quinoline-containing half-salamo-type ligand

A quinoline-containing semi-salamo-type ligand, HL, was synthesized and a dinuclear Ni(II) complex, [Ni2(L)2(NCS)2], was produced. The complex was experimentally analyzed by elemental analysis, fluorescence, and UV–Vis spectroscopy. X-ray single crystal diffraction experiments showed that the complex is a six-coordinate, structurally symmetric, phenoxy-bridged dinuclear Ni(II) dimer with the participation of SCN− in the coordination to satisfy charge neutrality. The self-assembly forms a 2-D supramolecular network structure through hydrogen bonding and π⋯π interactions. DFT calculations were performed on the complex to analyze its energy gaps, and UV–Vis experiment was verified by TD-DFT calculation. In addition, close intermolecular contacts were investigated by Hirshfeld surface analysis to quantify the crystal structure interaction.

Abnormal N-heterocyclic Carbene Based Ni(II) π-allyl Complex towards Molecular Oxygen Activation.

Abnormal N-heterocyclic carbene (aNHC) based Ni(II) π-allyl complexes (3 and 4) were synthesized starting from a Ni(0) precursor. These complexes were characterized by NMR spectroscopy, single-crystal X-ray crystallography (4) and elemental analysis data. The underlying mechanism for the formation of Ni(II) η3 -allyl complexes from a Ni(0) precursor on treatment with a free abnormal N-heterocyclic carbene in absence of any external additive or oxidant was unraveled. Later, complex 3 was exposed to O2 gas under ambient pressure resulting in molecular oxygen activation to form a μ-hydroxo bridged Ni(II) dimer.

Selective Synthesis of Z-Silyl Enol Ethers via Ni-Catalyzed Remote Functionalization of Ketones.

We report a remote functionalization strategy, which allows the Z-selective synthesis of silyl enol ethers of (hetero)aromatic and aliphatic ketones via Ni-catalyzed chain walking from a distant olefin site. The positional selectivity is controlled by the directionality of the chain walk and is independent of thermodynamic preferences of the resulting silyl enol ether. Our mechanistic data indicate that a Ni(I) dimer is formed under these conditions, which serves as a catalyst resting state and, upon reaction with an alkyl bromide, is converted to [Ni(II)-H] as an active chain-walking/functionalization catalyst, ultimately generating a stabilized η3-bound Ni(II) enolate as the key selectivity-controlling intermediate.

Double atom-anchored Defective Boron Nitride catalyst for efficient electroreduction of CO2 to CH4: A first principles study

A series of electrocatalysts of double transition metal atoms (Mn to Cu) supported on defective BN monolayers were investigated for the electrocatalytic CO2 reduction (CO2RR) using a first-principles calculation. The detailed CO2RR mechanisms were identified based on free energy calculations. The thermodynamic results revealed that Fe dimer, Ni dimer and CuMn heteronuclear dimer anchored BN nanosheet exhibited high CO2RR activity toward the production of CH4. The calculated limiting potential were −0.47 V, −0.39 V and −0.61 V for Fe2@BN, Ni2@BN and CuMn@BN catalysts, respectively. This work opens up new designs for highly efficient and low-cost BN-based nanocomposites for CO2RR.

Utilisation of new NiSNS pincer complexes in paraffin oxidation

Abstract Two series of closely related SNS pincer ligands (L) were synthesised with the major structural variation on the nitrogen backbone containing either the methyl [L = (RSCH2CH2)2NMe: where R = Me (1), Et (2), Bu (3)] or the phenyl [L = (RSCH2CH2)2NPh: where R = Me (4), Et (5), Cy (6)] functional group. When ligands 1–3 were complexed to Ni by reaction with Ni(DME)Cl2 (DME = dimethoxyethane), they respectively yielded three new cationic dimeric [LNi(μ-Cl)3NiL]+ complexes (7–9), whilst ligands 4–6 on reaction with Ni(PPh3)2Br2 respectively yielded neutral mononuclear (LNiBr2) complexes 10–12. All the new compounds were characterised by IR, HRMS, elemental analysis and in addition, single crystal X-ray diffraction for complexes 9–12. X-ray structural data of 9 revealed an unusual three chlorido-bridged Ni dimer with the SNS ligand coordinated in a facial binding mode to the two pseudo-octahedral Ni centres. Molecular structures of complexes 10, 11 and 12 each displayed five-coordinate distorted trigonal bipyramidal geometry around the nickel(II) metal centres. When utilised as catalysts in the tert-butyl hydroperoxide oxidation of n-octane, all the complexes showed activity to mainly products of internal carbon activation (octanones and secondary octanols) with 11 as the most active (10% total substrate to oxygenates yield), whereas 10 was the least active, but most selective towards alcohols (alcohol/ketone = 2.13).

Enhancement of hydrogen sorption on metal(Ni, Rh, Pd) functionalized carbon nanotubes: a DFT study

Hydrogen interacted with pristine single-walled carbon nanotubes(SWNTs) and single/dimer metal doped ones(M-CNTs) was investigated via density functional theory(DFT) simulations. The most stable configura-tions of Ni, Rh, Pd on SWNTs were identified. The interaction of H2 molecules with pristine SWNTs and M-CNTs was investigated. The results show that H2 molecules can be adsorbed on the pristine SWNTs via a weak physical in-teraction, which is much weaker than those of H2 molecules with M-CNTs by chemisorption. Each Ni, Rh and Pd doped SWNTs can respectively chemisorb three, two, or one H2 molecules and the H―H bond of H2 molecule is elongated. Furthermore, the H2 molecule could be dissociated owing to the presence of the Ni-Ni bond for Ni dimer doped SWNT, forming new Ni―H bonds. While such a dissociation could not be observed on Rh2/Pd2-CNT samples. Density of state(DOS) results show that the s orbital of hydrogen can hybridize with the d orbital of metal atom, re-sulting in the stronger inteaction between H2 and M-CNTs, impying that the hydrogen storage capacity could be en-hanced in the presence of M-CNTs. The comparison of the interaction mechanism among different metals doped CNTs can screen out the most effective hydrogen-adsorption materials and the design of the related materials by computational approaches.

A possible highly active supported Ni dimer catalyst for O2 dissociation: A first-principles study

The adsorption and dissociation of O2 on the supported small nickel clusters with one-, two-, three-Ni atoms on yttria-stabilized zirconia (YSZ) (111) surfaces, as well as those on the bare YSZ(111) and Ni(111) surfaces are comparatively studied using ab initio density functional theory calculations. It is found that the dissociation of O2 on the YSZ(111) surface is largely enhanced by the supported Ni dimer, which is predicted to be the smallest Ni cluster needed for efficient O2 dissociation. The results would provide an important reference to improve the activity and efficiency of the Ni/YSZ(111) nanocomposite catalysts in cost-effective materials.

Metal dimer sites in ZSM-5 zeolite for methane-to-methanol conversion from first-principles kinetic modelling: is the [Cu–O–Cu]2+motif relevant for Ni, Co, Fe, Ag, and Au?

Reaction energy landscapes for the direct conversion of methane to methanol over ZSM-5 for Cu, Ni, Co and Fe dimer sites.

Synthesis and Structures of Nickel Complexes with a PN-Chelate Phosphaalkene Ligand

Phosphaalkenes with a P═C bond possess extremely strong π-accepting ability, often providing transition metal complexes with interesting structures and properties. This paper describes unique structures of nickel complexes coordinated with a PN-chelate phosphaalkene ligand (PEP = 2-[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine). The PEP ligand combines with [NiBr2(dme)] (dme = 1,2-dimethoxyethane) in toluene to afford [Ni(Br)(μ-Br)(PEP)]2 (1), which reacts with R2Mg(thf)2 in Et2O or THF to form three types of nickel complexes depending on the R groups and reaction conditions. The reaction with Ph2Mg(thf)2 produces a Ni(I) dimer bridged with two μ-Br ligands, [Ni(μ-Br)(PEP)]2 (2). Treatment of 1 with R2Mg(thf)2 (R = Me, Me3SiCH2) at −35 °C leads to dialkyl complexes [NiR2(PEP)] (3 and 4), with a significantly distorted square planar configuration. DFT calculations support the occurrence of effective π-back-bonding between Ni to PEP to cause the structural distortion. On the other hand, the reaction of 1 with R2Mg(thf)2 (R = Me3SiCH2) conducted at a low temperature of −78 °C forms an aryl bromide complex of the formula [Ni(Mes*)(Br)(PEP*)] (5; Mes* = 2,4,6-tBu3C6H2), in which the Mes* group originally bonded to the phosphorus atom of PEP is shifted to nickel; instead, the phosphorus atom is substituted with the R group to form the PEP* ligand. The temperature-dependent formation of 4 or 5 is rationalized by considering a common five-coordinate intermediate.

Boryl-metal bonds facilitate cobalt/nickel-catalyzed olefin hydrogenation.

New approaches toward the generation of late first-row metal catalysts that efficiently facilitate two-electron reductive transformations (e.g., hydrogenation) more typical of noble-metal catalysts is an important goal. Herein we describe the synthesis of a structurally unusual S = 1 bimetallic Co complex, [((Cy)PBP)CoH]2 (1), supported by bis(phosphino)boryl and bis(phosphino)hydridoborane ligands. This complex reacts reversibly with a second equivalent of H2 (1 atm) and serves as an olefin hydrogenation catalyst under mild conditions (room temperature, 1 atm H2). A bimetallic Co species is invoked in the rate-determining step of the catalysis according to kinetic studies. A structurally related Ni(I)Ni(I) dimer, [((Ph)PBP)Ni]2 (3), has also been prepared. Like Co catalyst 1, Ni complex 3 displays reversible reactivity toward H2, affording the bimetallic complex [((Ph)PBHP)NiH]2 (4). This reversible behavior is unprecedented for Ni(I) species and is attributed to the presence of a boryl-Ni bond. Lastly, a series of monomeric ((tBu)PBP)NiX complexes (X = Cl (5), OTf (6), H (7), OC(H)O (8)) have been prepared. The complex ((tBu)PBP)NiH (7) shows enhanced catalytic olefin hydrogenation activity when directly compared with its isoelectronic/isostructural analogues where the boryl unit is substituted by a phenyl or amine donor, a phenomenon that we posit is related to the strong trans influence exerted by the boryl ligand.

Nickel Dimers Adsorbed on Graphene: First-Principles Study

The structural stabilities, electronic, and magnetic properties of Ni dimers adsorption on pure and single-vacancy graphene were studied using a first-principle method. It was found that structures of the Ni dimer adsorbed on single-vacancy graphene are more stable than those structures of the Ni dimer adsorbed on pure graphene. Total energy calculation results demonstrated that for Ni dimer adsorption on single-vacancy graphene and pure graphene, the most stable structure is PV2 where the Ni dimer is positioned perpendicular to the vacancy site and PH1 where Ni dimer standing perpendicular to hollow site. Furthermore, it indicated covalent bond was formed between Ni atoms and their nearest C atoms, suggestive of chemisorption. The structures where Ni dimer lay horizontal to the pure graphene layer (H(T1–T3), H(B1–B2), H(B1–B3)) showed strong magnetism, while the structures of dimer-adsorption structures on single-vacancy graphene do not exhibit magnetism. The electronic origin of magnetic states was located on Ni atoms, specifically the d orbit. The Ni dimer, positioned parallel to the graphene plane, offers the possibility for the formation of Ni atom chain or wire on graphene, which might have potential nanoelectronic applications.

Salicylaldimine Schiff bases – Generation of self-assembled and chiral complexes with Ni(II) and Zn(II) ions. An unusual antiferromagnetic interaction in a triply bridged Ni(II) dimer

Abstract Four new complexes of nickel(II) and zinc(II) with Schiff bases obtained from the condensation of salicylaldehyde and N,N-dimethyl-ethylene/propylenediamine and their reduced products have been synthesized and characterized by spectroscopic methods and single crystal X-ray structural analysis. Complex 1 is a six coordinated mononuclear complex of Ni(II), having a self assembled 2D structure with alternate cages and cavities running perpendicular to the c axis. The octagonal cavities are occupied by water molecules which are weakly hydrogen bonded to the eight oxygens lining the inner side of these cavities. Complex 2 is a phenoxo and aquo bridged dinuclear six coordinated complex of nickel(II) having two face sharing octahedra. Variable temperature magnetic susceptibility measurements of 2 show the presence of an antiferromagnetic coupling between the two nickel(II) centers. To the best of our knowledge it is the first dimeric complex of Ni(II), triply bridged by two phenoxo and one water molecule to show such a behavior. Complex 3 is a simple five coordinated monomer of Zn(II), whereas 4 is a chiral, dinuclear complex having zinc(II) ions with two different stereochemistries, which has been obtained by simultaneous resolution from achiral precursors.

Anion mediated formation of different Schiff bases from the same precursors and their nickel(II) complexes with different nuclearity

Two nickel(II) complexes, [Ni2 (H2O)4](NO3)2 (1) and [Ni5 (OAc)6(OH)2] · 5.5H2O (2), have been synthesized and structurally characterized by X-ray crystallographic study, where L1 and L2 represent 2-formyl-4-methyl-6-(1-(2-aminomethyl)piperidine)-iminomethylphenolate and 4-methyl-2,6-bis(1-(2-aminomethyl)piperidine)-iminomethylphenolate, respectively. One-pot reactions between 2,6-diformyl-4-methylphenol with 1-(2-aminoethyl)piperidine, in the presence of nickel(II) nitrate and nickel(II) acetate, afforded in situ [1 + 1] and [1 + 2] condensation leading to Schiff-bases HL1 and HL2, and to 1 and 2 of different nuclearity. Both processes were conducted under the same reaction conditions in anhydrous EtOH. Preferential attainment of bi- or pentanuclear compounds is mediated by the anion of the Ni(II) salt. Complex 1 is formed by two unsymmetrical tridentate L1 chelating in a head-tail fashion to make a centrosymmetric phenoxido-bridged Ni(II) dimer. Two waters complete octahedral coordination. Conversely in 2, two [Ni2(OAc)L2]+ units, having a syn-syn bidentate bridging acetate, embrace a third Ni through bridging acetate and μ3-hydroxide, giving rise to an adduct of C2 symmetry where the compartmental ligand planes form a dihedral angle of ca. 82°. The catecholase activity of these complexes were explored and both complexes effectively catalyze the conversion of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ).

Synthesis and Structural Diversity of Mono‐, Di‐ and Trinuclear Complexes with N,N′‐Bis[(2‐diphenylphosphanyl)phenyl]formamidine

AbstractThe synthesis, characterization, and coordination chemistry of a series of mono‐, di‐, and trinuclear homo‐/heterometallic complexes with the dinucleating ligand, N,N′‐bis[(2‐diphenyl‐phosphanyl)phenyl]formamidine (pnnp)1 are reported. Treatment of (pnnp)PdMe (1) with NiCl2(dme) forms the heterobimetallic (pnnp)PdMe(μ‐Cl)NiCl (3) complex, whereas reaction of 1 with Cu(CH3CN)4+PF6– yields the Pd···Cu···Pd heterometallic trinuclear complex (pnnp)Pd(Me)CuPd(Me)(pnnp)·PF6 (8). The reaction of pnnp with NiCl2(dme) (dme = 1,2‐dimethoxyethane) produces the Ni dimer [(pnnp)NiCl(μ‐Cl)]2 (5) or the dinuclear (pnnp)NiCl(μ‐X)NiCl (X = Cl or OH) (4) complexes, depending upon the stoichiometry. The reaction of pnnp with CoII or FeII ions leads to the monometallic complexes (pnnp)CoCl2 (6) or (pnnp)FeCl2 (7), respectively. The dinuclear (pnnp)PdMe(μ‐Cl)NiCl (3) and (pnnp)NiCl(μ‐X)NiCl (X = Cl or OH) (4) complexes adopt A‐frame structures with two square‐planar d8 metal complexes hinged by the bridging ligand; the angles between the square planes correlate to the covalent radii, in which the smaller homo‐bimetallic Ni complex adopts a more coplanar arrangement of the two Ni square planes. The heterometallic trinuclear complex (pnnp)Pd(Me)CuPd(Me)(pnnp)·PF6 (8) adopts an unusual structure around the Cu center, suggestive of a weak d8–d10 interaction between the Pd and Cu atoms. All complexes have been characterized by NMR spectroscopy, elemental analysis, and X‐ray crystallography, and their structural diversity is discussed.

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.

Group-Transfer Reactions of Ni(II)−Ni(II) Bridging Imido Complexes. Catalytic Formation of Carbodiimides and Isocyanates via Nitrene Transfer from Organoazides

The NHC-supported Ni(I) dimer {(IPr)Ni(μ-Cl)}2 (1; IPr = 1,3-di(2,6-di-isopropylphenyl)imidazolin-2-ylidene) yields the bridging d8−d8 imido complex {(IPr)NiCl}2(μ-NMes) (2; Mes = 2,4,6-Me3C6H2) up...

Interaction of hydrogen molecules on Ni-doped single-walled carbon nanotube

Adsorption of hydrogen molecules on an Ni-doped (8,0) single-walled carbon nanotube (SWNT) is investigated by using first-principles density functional calculations. The result shows that a single Ni atom adsorbed on the bridge site of the tube could cannot dissociate the H2, however it can chemisorb three H2 at most, with the average binding energy per H2 suitable for the hydrogen storage at the room temperature. More H2 would physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer adsorbed, we find that when the H2 approaches the Ni–Ni bond, it dissociates without overcoming any barrier and makes bonds with Ni atom.

A Dinuclear Ni(I) System Having a Diradical Ni2N2Diamond Core Resting State: Synthetic, Structural, Spectroscopic Elucidation, and Reductive Bond Splitting Reactions

One-electron reduction of the square-planar nickel precursor (PNP)NiCl ( 1) (PNP (-) = N[2-P(CHMe 2) 2-4-methylphenyl] 2) with KC 8 effects ligand reorganization of the pincer ligand to assemble a Ni(I) dimer, [Ni(mu 2-PNP)] 2 ( 2), containing a Ni 2N 2 core structure, as inferred by its solid-state X-ray structure. Solution magnetization measurements are consistent with a paramagnetic Ni(I) system likely undergoing a monomer <--> dimer equilibrium. The room-temperature and 4 K solid-state X-band electron paramagnetic resonance (EPR) spectra display anisotropic signals. Low-temperature solid-state X-band EPR data at 4 K reveal rhombic values g z = 1.980(4), g x = 2. 380(4), and g y = 2.225(4), as well as a forbidden signal at g = 4.24 for the Delta M S = 2 half field transition, in accord with 2 having two weakly interacting metal centers. Utilizing an S = 1 model, full spin Hamiltonian simulation of the low-temperature EPR spectrum on the solid sample was achieved by applying a nonzero zero-field-splitting parameter ( D = 0.001 cm (-1)), which is consistent with an S = 0 ground state with a very closely lying S = 1 state. Solid-state magnetization data also corroborate well with our solid-state EPR data and reveal weak antiferromagnetic behavior ( J = -1.52(5) cm (-1)) over a 2-300 K temperature range at a field of 1 Tesla. Evidence for 2 being a masked "(PNP)Ni" scaffold originates from its reaction with N 2CPh 2, which traps the Ni(I) monomer in the form of a T-shaped species, Ni(PNPNNCPh 2), a system that has been structurally characterized. The radical nature of complex 2, or its monomer component, is well manifested through the plethora of cooperative H-X-type bond cleavage reactions, providing the nickel(II) hydride (PNP)NiH and the corresponding rare functionalities -OH, -OCH 3, -PHPh, and -B(catechol) integrated into the (PNP)Ni moiety in equal molar amounts. In addition to splitting H 2, compound 2 can also engage in homolytic X-X bond cleavage reactions of PhXXPh to form (PNP)Ni(XPh) (X = S or Se).