Anionic Nickel Research Articles

Exploring structures of small anionic nickel-ethanol clusters with infrared spectroscopy.

Small anionic nickel clusters with ethanol are investigated with a combination of mass-selective infrared photodissociation spectroscopy in a molecular beam and density functional theory simulations at the BLYP/6-311g(d,p) and TPSSh/def2-TZVPP level. In this context, the O-H stretching vibration of the ethanol is analyzed to obtain information about the structural motif, the geometry of the metal core, and the spin state of the clusters. For the [Ni2(EtOH)]- and [Ni3(EtOH)]- clusters, we assign quartet states of motifs with a hydrogen bond from the ethanol to the linear nickel core. The aggregation of a further ethanol molecule, yielding the [Ni3(EtOH)2]- cluster, results in the formation of a cooperative hydrogen bond network between the nickel core and the two ethanol molecules.

Structural modification of nickel tetra(thiocyano)corroles during electrochemical water oxidation.

In this study, we present two fully characterized nickel tetrathiocyanocorroles, representing a novel class of 3d-metallocorroles. These nickel(II) ions form square planar complexes, exhibiting a d8-electronic configuration. These anionic complexes are stabilized by the electron-withdrawing SCN groups on the bipyrrole unit of the corrole. The reduced aromaticity in these anionic nickel(II) corrole complexes is evidenced by single crystal X-ray diffraction (XRD) data and a markedly altered absorption profile, with stronger Q bands compared to Soret bands. Notably, the UV-Vis and electrochemical data exhibit significant differences from previously reported nickel(II) corrole radical cation and nickel(II) porphyrin complexes. While these electrochemical data bear a resemblance to those of the anionic nickel(II) corrole by Gross et al., the UV-Vis data show substantial distinctions. Additionally, we explore the utilization of nickel(II)-corrole@CC (where CC denotes carbon cloth) as an electrocatalyst for the oxygen evolution reaction (OER) in an alkaline medium. During electrochemical water oxidation, the molecular catalyst is partially converted to nickel (oxy)hydroxide, Ni(O)OH. The structure reveals the coexistence of the molecular complex and Ni(O)OH in the active catalyst, achieving a turnover frequency (TOF) of 3.32 × 10-2 s-1. The synergy between the homogeneous and heterogeneous phases improves the OER activity, providing more active sites and edge sites and enhancing interfacial charge transfer.

Anionic nickel and nitrogen effects in the chiral antiferromagnetic antiperovskite Mn3NiN.

Magnetic antiperovskites, having chiral noncollinear antiferromagnetic ordering, have shown remarkable properties that range from negative thermal expansion to anomalous Hall effects. Nevertheless, details on the electronic structure, related to the oxidation states and the octahedral center's site effects, are still scarce. Here, we show a theoretical study, based on first-principles calculations in the framework of density-functional theory (DFT), on the electronic properties associated with the nitrogen site effects on the structural, electronic, magnetic, and topological degrees of freedom. Thus, we show that the nitrogen vacancy increases the value of the anomalous Hall conductivity and retains the chiral Γ4g antiferromagnetic ordering. Moreover, we reveal, based on the Bader charges and the electronic structure analysis, the negative and positive oxidation states of the Ni- and Mn-sites, respectively. This is in agreement with the expected A3α+Bβ-Xδ- oxidation states to satisfy charge neutrality in antiperovskites, but the negative charge is rare for transition metals. Finally, we extrapolate our findings on the oxidation states to several Mn3BN compounds, showing that the antiperovskite structure is an ideal platform to encounter negative oxidation states for metals sitting at the corner B-sites.

Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp2)-C(sp3) Coupling.

We use a ligand design strategy to isolate a cyclometalated nickel(IV) complex that is directly analogous to a key intermediate proposed in aminoquinoline-directed C-H functionalization catalysis. This nickel(IV) complex is formed by oxidative addition of a diaryliodonium reagent to an anionic nickel(II)-picolinate precursor. The nickel(IV) σ-aryl complex is stable at room temperature but undergoes C(sp2)-C(sp3) bond-forming reductive elimination under mild conditions (70 °C, 120 min). Overall, this study demonstrates the accessibility of long-sought-after nickel(IV) intermediates in C-H functionalization catalysis. Furthermore, it demonstrates that LX-type (bidentate, mono-anionic) ligands such as picolinate dramatically stabilize these nickel(IV) species.

Synthesis, Structure, and Hydroboration Reactivity of Anionic Nickel(0) Complexes Supported by Bidentate NHC-Pyridone Ligands

A family of anionic, formally nickel(0) complexes supported by bidentate NHC–pyridone ligands is described. The unsymmetric chelating environment and capping [K(18-crown-6)]+ countercation allow isolation of single-component, monometallic complexes in high yield. The steric and electronic properties are assessed through a battery of experimental (NMR, IR, UV–vis, X-ray diffraction) and computational tools. Catalytic activity for highly branched-selective hydroboration of styrene with HBpin is demonstrated. Control experiments implicate an important role of the pyridone in establishing reactivity and regioselectivity, suggesting the potential to leverage secondary coordination sphere effects with these single-component precatalysts for reagent activation and delivery.

Tricyanoborane-Functionalized Anionic N-Heterocyclic Carbenes: Adjustment of Charge and Stereo-Electronic Properties.

The 1‐methyl‐3‐(tricyanoborane)imidazolin‐2‐ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3‐methylimidazole adduct 1. Regarding charge and stereo‐electronic properties, anion 2 closes the gap between well‐known neutral NHCs and the ditopic dianionic NHC, the 1,3‐bis(tricyanoborane)imidazolin‐2‐ylidenate dianion (IIb). The influence of the number of N‐bonded tricyanoborane moieties on the σ‐donating and π‐accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3‐dimethylimidazolin‐2‐ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)4] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (%V bur) and σ‐donor and π‐acceptor abilities of NHCs can be effectively fine‐tuned via the number of tricyanoborane substituents.

Intricate Road to Linear Anionic Nickel(I) Hexamethyldisilazanide [Ni(N(SiMe3)2)2

In this report, we present intricate pathways for the synthesis of linear nickel(I) silylamide K{m}[Ni(NR2)2] (NR2 = -N(SiMe3)2). This is achieved first via the reduction of nickel(II) trisamide Li(donor)4[Ni(NR2)3] (Li(thf)x[1]) with KC8 in the presence of 18-crown-6 or crypt.222. In due course, the behavior of Li(donor)4[Ni(NR2)3] as a source of masked two-coordinate nickel(II) hexamethyldisilazanide is explored, leading to the formation of nickel(I) and nickel(II) N-donor adducts, as well as metal-metal-bonded dinickel(I) trisamide K(toluene)[Ni2(NR2)3] (K(toluene)[5]). Finally, a convenient and reliable synthesis of K{m}[Ni(NR2)2] by ligand exchange of phosphines in [Ni(NR2)(PPh3)2] with K{m}(NR2) is presented. This allows for the comprehensive analysis of its electronic properties which reveals a fluxional behavior in solution with tight anion/cation interactions.

Asymmetric Propargylic Substitution Enabled by Synergistic Nickel and Chiral Anion Catalysis

Asymmetric Propargylic Substitution Enabled by Synergistic Nickel and Chiral Anion Catalysis

On the Synthesis of a T‐Shaped Imido Nickel Complex and Trigonal Amido Nickel Complexes

AbstractThe synthesis of a T‐shaped imido nickel complex is reported, obtained by the reaction of phenyl azide with the linear nickel(I) silylamide complex K{18‐crown‐6}[NiL2] (L=−N(Dipp)SiMe3; Dipp=2,6‐diisopropylphenyl). In addition, an unusual shift of a SiMe3 unit from an ancillary ligand to a putative [Ni=NPh] complex is observed. Examination of the resulting [Ni=NDipp] complex for its electronic properties leads to its description as a low‐spin nickel(III) imide and revealed only limited activity with respect to H‐atom abstraction from C−H bonds or nitrene. Attempts to obtain information about the general features of trigonal nickel(II) amide products, that would result from such a H‐atom abstraction reaction, via reaction of linear nickel(II) silylamide [NiL2] with alkali metal salts of primary amides revealed the reduction to the linear nickel(I) complex K{18‐crown‐6}[NiL2]. The same is observed for alkoxides, secondary amides or benzyl. Reaction of the organic salts with the anionic nickel(II) complex NBu4[NiBrL2] under salt elimination also give the linear nickel(I) complex. Partial formation of an otherwise stable T‐shaped nickel(II) can be observed only for the electron‐poor diphenyl amide. This implicates that reduction of the starting nickel(II) complexes by different organic alkali metal salts likely does not occur via a homolytic Ni−R bond cleavage but a direct SET process from the unligated substrate to the nickel(II) ion.

1-Butyl-3-methyl-imidazolium tri-bromido-(tri-phenyl-phosphane-κP)nickelate(II) butan-1-ol hemisolvate.

The solvated title salt, (C8H15N2)[NiBr3(P(C6H5)3)]·0.5C4H10O, was obtained in the form of single crystals directly from the reaction mixture. The mol-ecular structure consists of separated 1-butyl-3-methyl-imidazolium cations, tri-bromido-(tri-phenyl-phosphane)nickelate(II) anions and half a solvent mol-ecule of 1-butanol, all connected via multiple hydrogen contacts to form a three-dimensional network. The co-crystallized 1-butanol mol-ecule is disordered and adopts two orientations. The central C-C bonds of both orientations are located on an inversion centre (Wyckoff site 2b of space group P21/n). Thereby, each orientation has again two orientations with the OH group being located either on one or the other side of the C4 alkyl chain. The dried solvent-free compound exhibits a relatively low melting point (m.p. = 412 K).

A convenient method for preparing the ionic Nickel (bis-dithiolene) complexes

Three anionic Nickel (bis-dithiolene) complexes have been conveniently synthesized by utilizing the neutral metal dithiolene complexes on the presence of triethylamine as a reductive reagent, and their physicochemical properties have been characterized. The results indicate that the new approach is suitable to prepare the ionic Nickel (bis-dithiolene) complexes.

Ni(ii) dithiolate anion composites with two-dimensional materials for electrochemical oxygen evolution reactions (OERs)

A redox active anionic nickel dithiolate complex was synthesized and its composites with GO, rGO and GN were prepared and used as electrocatalyts in the OER.

The Plasmonic Effect of Gold Nanorods on Charged Molecules: SERRS and SEF effects

Target molecules adsorbed onto metallic nanoparticles can have their Raman and/or fluorescence signals enhanced, leading to the called surface-enhanced [resonance] Raman scattering (SE[R]RS) or surface-enhanced fluorescence (SEF). Here we have applied Au nanorods (AuNRs) coated with a surfactant bilayer leading to a positive surface charge to investigate the role played by these AuNRs in colloidal suspension on SERRS and SEF effects of charged molecules. In the case of the anionic nickel (II) tetrasulfonated phthalocyanine (NiTsPc), besides achieving SERRS with an enhancement factor (EF) of ca. 105, the AuNRs allowed the analytical application of the SERRS effect for the NiTsPc between 8.3x10-6 and 4.0x10-5 mol L-1. The limit of detection of 4.8x10-7 mol L-1 (at 752 cm-1) and 1.3x10-6 mol L-1 (at 1338 cm-1) was found. In the case of the cationic methylene blue, the SEF effect was achieved reaching an EF of ca. 10. Besides, fundamental discussions are carried out considering the results presented here.

Electrocatalytic Oxidation of Ethinyl Estradiol by an Iron Oxide Nanoparticle/Nickel Phthalocyanine Supramolecular Electrode

Indium-doped tin oxide (ITO) substrates were surface-modified with layer-by-layer nanocomposite films of anionic nickel(II) tetrasulfonated phthalocyanine (NiTsPc) and positively charged iron oxide...

Crystal and molecular structure of [Ni{2-H2NC(=O)C5H4N}2(H2O)2][Ni{2,6-(O2C)2C5H3N}2]·4.67H2O; DFT studies on hydrogen bonding energies in the crystal.

[Ni{2-H2NC(=O)C5H4N}2(H2O)2][Ni{2,6-(O2C)2C5H3N}2]·4.67H2O, a new complex salt containing a bis(2,6-dicarboxypyridine)nickel(II) anion and a bis(2-amidopyridine)diaquanickel(II) cation, was synthesized and characterized. The crystal is stabilized by an extensive network of hydrogen bonds. Alternate layers of anions and cations/water molecules parallel to (010) can be distinguished. Computational studies of the network packing of the title compound by high-level DFT-D/B3LYP calculations indicate stabilization of the networks with conventional and non-conventional intermolecular O-H...O, N-H...O and C-H...O hydrogen bonds along with π-stacking contacts. Due to the presence of water molecules and the importance of forming hydrogen bonds with the involvement of water clusters to the stability of the crystal packing, the importance and role of these water clusters, and the quantitative stability resulting from the formation of hydrogen bonds and possibly other noncovalent bonds such as π-stacking are examined. The binding energies obtained by DFT-D calculations for these contacts indicate that hydrogen bonds, especially O-H...O and N-H...O, control the construction of the crystalline packing. Additionally, the results of Bader's theory of AIM for these interactions agree reasonably well with the calculated energies.

(MeCN)Ni(CF3)3]- and [Ni(CF3)4]2-: Foundations toward the Development of Trifluoromethylations at Unsupported Nickel.

Nickel anions [(MeCN)Ni(CF3)3]- and [Ni(CF3)4]2- were prepared by the formal addition of 3 and 4 equiv, respectively, of AgCF3 to [(dme)NiBr2] in the presence of the [PPh4]+ counterion. Detailed insights into the electronic properties of these new compounds were obtained through the use of density functional theory (DFT) calculations, spectroscopy-oriented configuration interaction (SORCI) calculations, X-ray absorption spectroscopy, and cyclic voltammetry. The data collectively show that trifluoromethyl complexes of nickel, even in the most common oxidation state of nickel(II), are highly covalent systems whereby a hole is distributed on the trifluoromethyl ligands, surprisingly rendering the metal to a physically more reduced state. In the cases of [(MeCN)Ni(CF3)3]- and [Ni(CF3)4]2-, these complexes are better physically described as d9 metal complexes. [(MeCN)Ni(CF3)3]- is electrophilic and reacts with other nucleophiles such as phenoxide to yield the unsupported [(PhO)Ni(CF3)3]2- salt, revealing the broader potential of [(MeCN)Ni(CF3)3]- in the development of "ligandless" trifluoromethylations at nickel. Proof-in-principle experiments show that the reaction of [(MeCN)Ni(CF3)3]- with an aryl iodonium salt yields trifluoromethylated arene, presumably via a high-valent, unsupported, and formal organonickel(IV) intermediate. Evidence of the feasibility of such intermediates is provided with the structurally characterized [PPh4]2[Ni(CF3)4(SO4)], which was derived through the two-electron oxidation of [Ni(CF3)4]2-.

Synthesis, structure, spectra, magnetism, non-linear optical properties and DFT calculations of a bis(dithiolene)nickel(III) anion salt with substituted isoquinolinium

Self-assemble of the bis(maleonitriledithiolate)nickel(III) anion ([Ni(mnt)2]−) and 4-cyanobenzyl isoquinolinium cation ([4CNBzIQl]+) results into a new molecular solid, [4CNBzIQl][Ni(mnt)2](1). Single crystal X-ray diffraction revealed that contains segregated columns of anions and cations and the Ni(III) ions form a 1 D zigzag alternating chain through Ni···S and π···π interactions between anions. Powder XRD diffraction study confirms the crystalline nature of the title material. The UV-Vis spectral analysis was used to determine the band gap energy, and the nonlinear optical (NLO) effect of the compound was predicted using DFT. Upon the temperature is lowered, the non-uniform chain has been compressed with the change of Ni···Ni distance, and a spin gap transition around 128 K.

Gas‐Phase Dehydrogenation of Alkanes: C−H Activation by a Graphene‐Supported Nickel Single‐Atom Catalyst Model

AbstractA gas‐phase anionic nickel(0) fluorenyl complex is shown to effect the dehydrogenation of linear, branched, and cyclic alkanes via C−H activation. It performs dehydrogenations via a C−H insertion followed by β‐hydride elimination. When given energy via collision‐induced dissociation, the system is capable of second and third dehydrogenations to form dienes and aromatics such as benzene. Kinetic isotope effects and DFT calculations completed at the M06/6–311+G** level support the proposed mechanism. The metal complex can act as an experimental model for graphene‐supported nickel single‐atom catalysts and suggests that these catalysts are capable of alkane dehydrogenation via C−H activation.

Gas-Phase Dehydrogenation of Alkanes: C-H Activation by a Graphene-Supported Nickel Single-Atom Catalyst Model.

A gas-phase anionic nickel(0) fluorenyl complex is shown to effect the dehydrogenation of linear, branched, and cyclic alkanes via C-H activation. It performs dehydrogenations via a C-H insertion followed by β-hydride elimination. When given energy via collision-induced dissociation, the system is capable of second and third dehydrogenations to form dienes and aromatics such as benzene. Kinetic isotope effects and DFT calculations completed at the M06/6-311+G** level support the proposed mechanism. The metal complex can act as an experimental model for graphene-supported nickel single-atom catalysts and suggests that these catalysts are capable of alkane dehydrogenation via C-H activation.

Metal organic frameworks derived hierarchical hollow Ni0.85Se|P composites for high-performance hybrid supercapacitor and efficient hydrogen evolution

Hollow nano-/micromaterials with tunable shell architectures and compositions are becoming increasingly important and attractive for electrochemical energy conversion and storage. Here, we report carbon-incorporated mixed anionic nickel phosphorus-selenium (Ni0.85Se|P) hollow yolk-shell microspheres synthesized by simultaneous selenization and phosphatization of Ni-based metal organic framework (Ni-MOF). Our experimental results indicated that P-doping reduces the synthesis temperature of the system and enhances the crystallinity of Ni0.85Se. As a result, this unique structure (Ni0.85Se|P) with better crystallinity and higher Ni2+/Ni3+ ratio shows outstanding specific capacity of 506 C g−1 at 1 A g−1. And the assembled Ni0.85Se|P//AC hybrid supercapacitor shows high power density of 20.7 Wh kg−1 at energy density of 798.7 W kg−1. Meanwhile, Ni0.85Se|P exhibits smaller Tafel slope of 90 mV dec−1 and lower onset overpotential of 179 mV versus reversible hydrogen electrode (RHE) for hydrogen evolution reaction (HER) than that of NiP2 and Ni0.85Se, which demonstrates the modulated electronic structure of Ni0.85Se|P. Our study will provide a new strategy for combining P-doped induced high crystallinity mixed anion transition metal complexes with MOF of hollow structures for energy storage device and HER.