Ni Center Research Articles

Multiphysics THz Antenna Simulations

The electrical response of an antenna-coupled nanothermocouple depends on how well the antenna converts incident optical energy to heat, and how this heat is converted to electrical signals by the nanothermocouples. In this paper, we study by COMSOL simulations the heat dissipated in dipole antennas operating at 600 GHz to maximize the temperature at the center of the antenna where the nanothermocouples are attached. We study antennas constructed from all-Au, all-Ni, and Au with Ni center segment. We also study the heat loss into the Si substrate, and use various thicknesses of SiO2 for thermal insulation from the substrate. We also discuss our simulation setup and our symmetric, geometry-independent mesh structure to avoid a variety of simulation errors and artifacts.

Activation of defective nickel molybdate nanowires for enhanced alkaline electrochemical hydrogen evolution.

Designing highly-efficient and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) in an alkaline solution is more complex and sluggish than for an acidic one. Herein, we report a controllable N-doping strategy to synthesize a series of N-doped porous metallic NiMoO4 nanowires with concomitant oxygen vacancy defects (N-Vo-NiMoO4 NWs) for promoting the alkaline HER ability and durability. Both experimental and theoretical results demonstrate that the doped-N at NiO6 octahedral sites and the abundant oxygen vacancy defects confined in N-Vo-NiMoO4 NWs with modified electronic arrangement could enhance the metallic conductivity, affect the surface areas, and lower the adsorption energy of hydrogen, resulting in an increased HER property. However, the excess doped-N leads to an opposite effect due to the reduced valence state of Ni centres. Therefore, alkaline HER ability of N-Vo-NiMoO4 NWs exhibits a volcano-like trend vs. the nitrogen content, with N3-Vo-NiMoO4 NWs being the best one. As a result, the N3-Vo-NiMoO4 NWs show nearly zero onset overpotential, an overpotential of 55 mV at 10 mA cm-2, and a Tafel slope of only 38 mV dec-1 in 1.0 M KOH, which are superior to those of state-of-the-art platinum-free electrocatalysts.

Evaluating the solvation properties of metal-containing ionic liquids using the solvation parameter model.

Ionic liquids (IL) have been utilized as gas chromatography stationary phases due to their high thermal stability, negligible vapor pressure, wide liquid range, and the ability to solvate a range of analytes. In this study, the solvation properties of eight room temperature ILs containing various transition and rare earth metal centers [e.g., Mn(II), Co(II), Ni(II), Nd(III), Gd(III), and Dy(III)] are characterized using the Abraham solvation parameter model. These metal-containing ILs (MCILs) consist of the trihexyl(tetradecyl)phosphonium cation and functionalized acetylacetonate ligands chelated to various metals. They are used in this study as gas chromatographic stationary phases to investigate the effect of the metal centers on the separation selectivities for various analytes. In addition, two MCILs comprised of tetrachloromanganate and tris(trifluoromethylphenylacetylaceto)manganate anions were used to study the effect of chelating ligands on the selectivity of the stationary phases. Depending on the metal center and chelating ligand, significant differences in solvation properties were observed. MCILs containing Ni(II) and Mn(II) metal centers exhibited higher retention factors and higher peak asymmetry factors for amines (e.g., aniline and pyridine). Alcohols (e.g., phenol, p-cresol, 1-octanol, and 1-decanol) were strongly retained on the MCIL stationary phase containing Mn(II) and Dy(III) metal centers. This study presents a comprehensive evaluation into how the solvation properties of ILs can be varied by incorporating transition and rare earth metal centers into their structural make-up. In addition, it provides insight into how these new classes of ILs can be used for solute-specific gas chromatographic separations. Graphical abstract The solvation properties of eight metal-containing ionic liquids (MCILs) comprised of transition and rare-earth metal centers are evaluated for the first time using gas chromatography. The results reveal that metals comprising the MCILs provide unique separation selectivities for various analytes and that these materials can be exploited as stationary phases in solute-specific gas chromatographic separations.

Oxygen Atom Transfer to Cationic PCPNi(II) Complexes Using Amine-N-Oxides.

Three PCsp3P pincer ligands differing in the aryl group linking the phosphine arms with the anchoring carbon donor were used to support square planar Ni(II) bromide complexes 1-3Br. Exchange of the coordinating bromide anion for the more weakly coordinating triflate (OTf) or hexafluoroantimonate (SbF6) anions was accomplished by treatment with AgX or TlX salts to give compounds 1-3X; compounds 1OTf, 1SbF6, 2Br, 2OTf, 3Br, and 3SbF6 were all characterized by X-ray crystallography. The reactions of these Ni(II) compounds with the amine-N-oxide oxygen atom transfer agents ONMe3 and ONMePh2 were explored. For ONMe3, reactions with 2 equiv gave products in which one arm of the pincer ligand was oxidized to a P═O unit, with the other amine-N-oxide ligated to the Ni(II) center, forming products 5-6X; compounds 4OTf, 5OTf, and 6SbF6 were characterized crystallographically. Transient amine-N-oxide adducts prior to ligand oxidation were observed in some reactions. For the more effective O atom donor ONMePh2, reactions were very rapid and a second oxidation of the remaining phosphine arm was observed, producing a Ni(II) species with an OCO pincer ligand (7SbF6). All compounds were fully characterized. Experiments aimed at trapping transient Ni(IV) oxo intermediates (with cyclohexadiene, KH, and various Lewis acids) indicated that such species were not involved in the reaction. This was supported by density functional theory (DFT) computations at the B3PW91 level, which indicated that direct O atom insertion into the Ni-P bonds without the intermediacy of a Ni oxo species was the low-energy pathway.

Pentanuclear Heterometallic String Complexes with High‐Bond‐order Units [Ni23+−Mo24+−Ni2+(bna)4X2]3+ (X = Cl, NCS)

Our quest for ligands toward the synthesis of functional metal string complexes started from α‐pyridylamido anions. With the modulation of naphthyridylamido anions, the ligands carry less negative charge to be balanced and, thus, to some extent, can tune the oxidation state of the metal centers and the strength of metal–metal interactions. For example, the formation of Ni23+, a mixed‐valence moiety, has been demonstrated. In this paper, high‐bond‐order units of M2 (Mo2 or Ru2) and Ni23+ are introduced and supported by four equatorial ligands of the bisnaphthyridylamido anion (bna−). The resulting compounds are [Ni2Mo2Ni(bna)4Cl2](PF6)3 (1), [Ni2Mo2Ni(bna)4(NCS)2](PF6)3 (2), and [Ni2Ru2Ni(bna)4Cl2](ClO4)3 (3). X‐ray crystallography reveal quadruply bonded characteristics with Mo–Mo distances of 2.133(2) and 2.109(2) Å for 1 and 2, respectively. The Ni2 moieties have a short Ni–Ni distance of 2.331(5) for 1 and 2.334(4) Å for 2, suggesting the formation of mixed‐valence Ni23+ units. It appears that there are no significant metal–metal interactions between Mo2 and its neighboring Ni centers. Characterization using magnetism, voltammetry, electronic absorption, and single‐molecule conductance, however, shows significant influence of Mo2 on the properties of the metal string complexes.

Metal organic frameworks-derived sensing material of SnO2/NiO composites for detection of triethylamine

The SnO2/NiO composites were synthesized by hydrothermal followed by calcination using metal-organic framework (MOF) consisting of the ligand of p-benzene-dicarboxylic acid (PTA) and the Sn and Ni center ions as sacrificial templates. The structure and morphology of Sn/Ni-based MOF and SnO2/NiO composites were characterized by XRD, SEM, TEM, FT-IR, TG, XPS and Brunauer-Emmett-Teller analysis. Sensing experiments reveal that the SnO2/NiO composite with the molar ratio of 9:1 not only exhibits the highest response of 14.03 that is 3 times higher than pristine SnO2 to triethylamine at 70 °C, but also shows good selectivity. Such excellent performance is attributed to the MOF-driven strategy and the formation of p-n heterojunctions, because the metal ions can be highly dispersed and separated in the MOFs and can prevent the metal ions aggregation during the MOF decomposition process. The work is a novel route for synthesis of gas sensing material.

Ranking the Stability of Transition-Metal Complexes by On-Surface Atom Exchange.

Surface-adsorbed macrocycles exhibit a number of interesting physical and chemical properties; many of them are determined by their transition-metal centers. The hierarchical exchange of the central metal atom in such surface-adsorbed complexes is demonstrated, specifically in the porphyrin-like macrocycle pyrphyrin adsorbed on Cu(111). Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, we show that Cu as central metal atom is easily exchanged with Ni or Fe atoms supplied in trace amounts to the surface. Atom exchange of Ni centers with Fe atoms also occurs, with moderate yield. These results allow ranking the stability of the surface-adsorbed Cu, Ni, and Fe complexes. The fact that the atom exchange occurs at 423 K shows that surface-adsorbed macrocycles can be surprisingly easily transformed.

Structural, electrochemical, and adsorption studies of Ni and Zn benzylimidazole coordination polymers with terephthalate linkers

Two coordination polymers, [Ni(bim)2(L1)(H2O)2] n (CP-1) and [Zn(bim)(L1)(Cl)] n (CP-2) (bim = 1-benzylimidazole, L1 = terephthalic acid), were synthesized and characterized by physicochemical and spectroscopic methods. The Ni(II) center in CP-1 is octahedral, while the Zn(II) center in CP-2 is tetrahedral. CP-1 and CP-2 were used to modify carbon paste electrodes to assess their effect on the electrochemical behavior of ferricyanide. The redox reactions of ferricyanide on both electrodes proved to be reversible and diffusion controlled, with ferricyanide diffusion coefficients for CP-1 and CP-2 of 1.88 × 105 and 3.44 × 105 cm2 s−1, respectively. These coordination polymers were also investigated for their adsorption behavior toward two dyes: Chicago sky blue and methylene blue. CP-1 and CP-2 both rapidly adsorbed the anionic Chicago sky blue dye by different intermolecular interactions; in contrast, the cationic methylene blue dye was adsorbed to a lesser extent. The adsorption of these CPs depends on the charge but not the size of the dye. Addition of methanolic potassium nitrate solution caused the release of the adsorbed dyes.

Synergistic Mechanistic Study of Nickel(0)/Lewis Acid Catalyzed Cyanoesterification: Effect of Lewis Acid

The highly selective nickel(0)-catalyzed cyanoesterification of cyanoformates with alkynes is greatly facilitated by Lewis acid (LA). We report density functional theory (DFT) investigations on the mechanistic details and provide a rational explanation of the “LA effect”. Our calculations disclose that an unusual biphosphine cycle including rate-determining oxidative addition of a C–CN bond, alkyne migratory insertion, and reductive elimination steps is more favorable than the generally accepted monophosphine cycle. The LA has a non-negligible impact on the mechanistic origin of selective C–CN bond activation. Furthermore, the presence of LA dramatically accelerates alkyne migratory insertion because the strong electron-withdrawing property of LA strengthens the coordination ability of the Ni center with alkyne to form the thermodynamically favorable five-coordinate nickel(II) cyanide carboxylate species, which then avoids the large deformation of the transition state of alkyne migration insertion to give...

B(C6F5)3 Promotes the catalytic activation of [N,S]-ferrocenyl nickel complexes in ethylene oligomerization

The synthesis of new methallyl-ferrocenyl-thiazoline-nickel complexes [1-(2-thiazolin-2-yl)-2-(R-thio)-ferrocene-κ2N,S]-(η3-methallyl)nickel(II) [Y] (1-3, R = Me, i-Pr, Ph, Y = BF4-4, R = Me, Y = BAr´4-) by reaction with 2-ferrocenyl-2-thiazoline ligands L1–3 with [Ni-(η3-(CH2)2CMe)Cl]2 in presence of fluoroborate salts (Y = BAr´4-; BF4-) is reported. The complexes 1–4 were obtained in high yields, and characterized by 1H, 13C, 19F and 11B NMR, FTIR. The X-Ray diffraction analysis of 4 confirmed the formation of a single isomer containing a nickel center coordinated to L1 in a bidentate [N,S] fashion and to a η3-methallyl ligand. These complexes catalyzed efficiently the ethylene oligomerization when tris(pentafluorophenyl)borane (BCF) was used as co-activator. All catalytic precursors produced C4 and C6 fractions. Complex 1 showed higher activity with TOF 3006 h-1 at room temperature with selectivity of 86% to C4 fraction. In contrast, catalyst 2 was more selective to the formation of 1-butene, but with low activity. DFT-Computational studies of complex-BCF adducts show than these species behave as frustrated Lewis pairs, mainly stabilized by long-range interactions enhancing the acceptor character of the complexes. Structural modifications over the sulfanyl group tune the acceptor character of Ni center, affecting their catalytic performance.

Crystalline Coordination Networks of Zero-Valent Metal Centers: Formation of a 3-Dimensional Ni(0) Framework with m-Terphenyl Diisocyanides.

A permanently porous, three-dimensional metal-organic material formed from zero-valent metal nodes is presented. Combination of ditopic m-terphenyl diisocyanide, [CNArMes2]2, and the d10 Ni(0) precursor Ni(COD)2, produces a porous metal-organic material featuring tetrahedral [Ni(CNArMes2)4]n structural sites. X-ray absorption spectroscopy provides firm evidence for the presence of Ni(0) centers, whereas gas-sorption andthermogravimetric analysis reveal the characteristics of a robust network with a microdomain N2-adsorption profile.

A Large Family of Halogen-Bonded Cocrystals Involving Metal–Organic Building Blocks with Open Coordination Sites

We demonstrate a design for halogen-bonded metal–organic cocrystals involving coordinatively unsaturated square-planar Cu(II) and Ni(II) centers, by utilizing a Schiff base ligand whose pendant acetyl group enables halogen bonding. The robustness of this design is evident by the assembly of a large family of eight cocrystals based on zero-, one-, and two-dimensional halogen bonded architectures involving mono- or ditopic halogen bond donors based on iodine or bromine.

A pair of enantiomeric trinuclear nickel (II) clusters based on chiral Schiff-base: Synthesis, structures, circular dichroism and magnetic properties

A pair of enantiomeric trinuclear Ni (II) clusters formulated as Ni3[(HLL-Thr)2(H2O)4(benzoate)2]·2EtOH (1) and Ni3[(HLD-Thr)2(H2O)4(benzoate)2]·2EtOH (2) (H3L=3-hydroxy-2-[(2-hydroxy-3-methoxy-benzylidene)-amino]-butyric acid), have been successfully synthesized via the assembly of a pair of enantiomerically chiral amino acid Schiff-base ligands, benzoate anion with divalent nickel salt in an air-exposed water-ethanol solutions. The structures are characterized through single-crystal-X-ray diffraction analysis. The structures of complex 1 and 2 both contain enantiomeric linear trinuclear Ni3[(HL)2(H2O)4(benzoate)2]·2EtOH units in which Ni (II) ions are bridged by the mixed bridges of (μ-Ophenol)2(μ-COO)2. Circular dichroism (CD) spectra indicated the enantiomeric nature of the pair of clusters. Magnetic susceptibility studies in the temperature range of 2–300K illustrated that complex 1 and 2 show ferromagnetic interactions between the Ni (II) centers within the trinuclear units while antiferromagnetic interactions among inter-trinuclear units.

Nickel-Catalyzed Copolymerization of Ethylene and Vinyltrialkoxysilanes: Catalytic Production of Cross-Linkable Polyethylene and Elucidation of the Chain-Growth Mechanism.

Copolymerizations of ethylene with vinyltrialkoxysilanes using cationic (α-diimine)Ni(Me)(CH3CN)+ complexes 4a,b/B(C6F5)3 yield high molecular weight copolymers exhibiting highly branched to nearly linear backbones depending on reaction conditions and catalyst choice. Polymerizations are first-order in ethylene pressure and inverse-order in silane concentration. Microstructural analysis of the copolymers reveals both in-chain and chain-end incorporation of -Si(OR)3 groups whose ratios depend on temperature and ethylene pressure. Detailed low-temperature NMR spectroscopic investigations show that well-defined complex 3b (α-diimine)Ni(Me)(OEt2)+ reacts rapidly at -60 °C with vinyltrialkoxysilanes via both 2,1 and 1,2 insertion pathways to yield 4- and 5-membered chelates, respectively. Such chelates are the major catalyst resting states but are in rapid equilibrium with ethylene-opened chelates, (α-diimine)Ni(R)(C2H4)+ complexes, the species responsible for chain growth. Chelate rearrangement via β-silyl elimination accounts for formation of chain-end -Si(OR)3 groups and constitutes a chain-transfer mechanism. Chelate formation and coordination of the Ni center to the ether moiety, R-O-Si, of the vinylsilane somewhat decreases the turnover frequency (TOF) relative to ethylene homopolymerization, but still remarkably high TOFs of up to 4.5 × 105 h-1 and overall productivities can be achieved. Activation of readily available (α-diimine)NiBr2 complexes 2 with a combination of AlMe3/B(C6F5)3/[Ph3C][B(C6F5)4] yields a highly active and productive catalyst system for the convenient synthesis of the copolymer, a cross-linkable PE. For example, copolymers containing 0.23 mol % silane can be generated at 60 °C, 600 psig ethylene over 4 h with a productivity of 560 kg copolymer/g Ni. This method offers an alternative route to these materials, normally prepared via radical routes, which are precursors to the commercial cross-linked polyethylene, PEX-b.

High Oxygen Reduction Reaction Performances of Cathode Materials Combining Polyoxometalates, Coordination Complexes, and Carboneous Supports.

A series of carbonaceous-supported precious-metal-free polyoxometalate (POM)-based composites which can be easily synthesized on a large scale was shown to act as efficient cathode materials for the oxygen reduction reaction (ORR) in neutral or basic media via a four-electron mechanism with high durability. Moreover, exploiting the versatility of the considered system, its activity was optimized by the judicious choice of the 3d metals incorporated in the {(PW9)2M7} (M = Co, Ni) POM core, the POM counterions and the support (thermalized triazine-based frameworks (TTFs), fluorine-doped TTF (TTF-F), reduced graphene oxide, or carbon Vulcan XC-72. In particular, for {(PW9)2Ni7}/{Cu(ethylenediamine)2}/TTF-F, the overpotential required to drive the ORR compared well with those of Pt/C. This outstanding ORR electrocatalytic activity is linked with two synergistic effects due to the binary combination of the Cu and Ni centers and the strong interaction between the POM molecules and the porous and highly conducting TTF-F framework. To our knowledge, {(PW9)2Ni7}/{Cu(ethylenediamine)2}/TTF-F represents the first example of POM-based noble-metal-free ORR electrocatalyst possessing both comparable ORR electrocatalytic activity and much higher stability than that of Pt/C in neutral medium.

Preparation of Labile Ni+(cyclam) Cations in the Gas Phase Using Electron-Transfer Reduction through Ion-Ion Recombination in an Ion Trap and Structural Characterization with Vibrational Spectroscopy.

Gas-phase ion chemistry methods that capture and characterize the degree of activation of small molecules in the active sites of homogeneous catalysts form a powerful new tool to unravel how ligand environments affect reactivity. A key roadblock in this development, however, is the ability to generate the fragile metal oxidation states that are essential for catalytic activity. Here we demonstrate the preparation of the key Ni(I) center in the widely used cyclam scaffold using ion–ion recombination as a gas-phase alternative to electrochemical reduction. The singly charged Ni+(cyclam) coordination complex is generated by electron transfer from fluoranthene and azobenzene anions to doubly charged Ni2+(cyclam), using the electron-transfer dissociation protocol in a commercial quadrupole ion trap instrument and in a custom-built octopole RF ion trap. The successful preparation of the Ni+(cyclam) cation is verified through analysis of its vibrational spectrum obtained using the infrared free electron laser FELIX.

Dinuclear Nickel Complexes of Thiolate-Functionalized Carbene Ligands and Their Electrochemical Properties.

Four dimeric nickel(II) complexes [Ni2Cl2(BnC2S)2] [1], [Ni2Cl2(BnC3S)2] [2], [Ni2(PyC2S)2]Br2 [3]Br2, and [Ni2(PyC3S)2]Br2 [4]Br2 of four different thiolate-functionalized N-heterocyclic carbene (NHC) ligands were synthesized, and their structures have been determined by single-crystal X-ray crystallography. The four ligands differ by the alkyl chain length between the thiolate group and the benzimidazole nitrogen (two −C2– or three −C3– carbon atoms) and the second functionality at the NHC being a benzyl (Bn) or a pyridylmethyl (Py) group. The nickel(II) ions are coordinated to the NHC carbon atom and the pendent thiolate group, which bridges to the second nickel(II) ion creating the dinuclear structure. Additionally, in compounds [1] and [2], the fourth coordination position of the square-planar Ni(II) centers is occupied by the halide ions, whereas in [3]2+ and [4]2+, the additional pendant pyridylmethyl groups complete the coordination spheres of the nickel ions. The electrochemical properties of the four complexes were studied using cyclic voltammetry and controlled-potential coulometry methods. The thiolate-functionalized carbene complexes [1] and [2] appear to be poor electrocatalysts for the hydrogen evolution reaction; the complexes [3]Br2 and [4]Br2, bearing an extra pyridylmethyl group, show higher catalytic activity in proton reduction, indicating that the pyridine group plays an important role in the catalytic cycle.

Magnetic field tunability of spin-polarized excitations in a high-temperature magnet

We bring together magnetic circular dichroism, photoconductivity, and complementary first-principles calculations in order to unravel spin-charge interactions in the high Curie temperature magnet ${\mathrm{NiFe}}_{2}{\mathrm{O}}_{4}$. Analysis uncovers a massive set of well-isolated spin-down states, a metamagnetic transition involving spin on the Ni center that switches the electronic structure of this system, and photoconductivity that depends on the magnetic field. These findings open the door for the creation and control of spin-polarized excitations from minority channel charge transfer in spinel ferrites.

Anomalous in situ Activation of Carbon-Supported Ni2P Nanoparticles for Oxygen Evolving Electrocatalysis in Alkaline Media

Electrochemical water splitting is one of the most promising systems by which to store energy produced from sustainable sources, such as solar and wind energy. Designing robust and stable electrocatalysts is urgently needed because of the relatively sluggish kinetics of the anodic reaction, i.e. the oxygen evolution reaction (OER). In this study, we investigate the anomalous in situ activation behaviour of carbon-supported Ni2P nanoparticles (Ni2P/C) during OER catalysis in alkaline media. The activated Ni2P/C shows an exceptionally high activity and stability under OER conditions in which the overpotential needed to achieve 10 mA cm−2 was reduced from approximately 350 mV to approximately 300 mV after 8,000 cyclic voltammetric scans. In situ and ex situ characterizations indicate that the activity enhancement of Ni2P catalysts is due to a favourable phase transformation of the Ni centre to β-NiOOH, including increases in the active area induced by structural deformation under the OER conditions. These findings provide new insights towards designing transition metal/phosphide-based materials for an efficient water splitting catalyst.

An XAS investigation of the nickel site structure in the transcriptional regulator InrS

InrS (Internal nickel-responsive Sensor) is a transcriptional repressor of the nickel exporter NrsD and de-represses expression of the exporter upon binding Ni(II) ions. Although a crystal structure of apo-InrS has been reported, no structure of the protein with metal ions bound is available. Herein we report the results of metal site structural investigations of Ni(II) and Cu(II) complexes of InrS using X-ray absorption spectroscopy (XAS) that are complementary to data available from the apo-InrS crystal structure, and are consistent with a planar four-coordinate [Ni(His)2(Cys)2] structure, where the ligands are derived from the side chains of His21, Cys53, His78, and Cys82. Coordination of Cu(II) to InrS forms a nearly identical planar four-coordinate complex that is consistent with a simple replacement of the Ni(II) center by Cu(II).