Ni-N Bond Research Articles

Calprotectin's Protein Structure Shields Ni-N(His) Bonds from Competing Agents.

The Ni-N(His) coordination bond, formed between the nickel ion and histidine residues, is essential for recombinant protein purification, especially in Ni-NTA-based systems for selectively binding polyhistidine-tagged (Histag) proteins. While previous studies have explored its bond strength in a synthetic Ni-NTA-Histag system, the influence of the surrounding protein structure remains less understood. In this study, we used atomic force microscopy-based single-molecule force spectroscopy (AFM-SMFS) to quantify the Ni-N(His) bond strength in calprotectin, a biologically relevant protein system. Our results demonstrate that the Ni-N(His) bond in protein exhibits a rupture force of ∼56 pN. Notably, kinetic analysis revealed a significantly lower off-rate compared to the synthetic system, suggesting that the protein environment plays a crucial role in stabilizing the bond. Moreover, we found that the bond is less susceptible to displacement by competing agents, such as imidazole, and experiences only a modest decrease in stability under acidic conditions, compared to the dramatic weakening seen in a synthetic system. These findings highlight the role of protein structure in protecting the mechanical and kinetic stability of the Ni-N(His) bond, offering insights into understanding the metal-ligand interactions in proteins in general.

Hydrophobic driving fabrication of highly dispersed PtNi in Zr-doped 3D hollow flower-like MgAl2O4 spheres with abundant O vacancies for enhanced dry reforming of methane.

The dry reforming of methane (DRM) could convert CH4 and CO2 into syngas, offering potential for greenhouse gas mitigation. However, DRM catalyst sintering and carbon deposition remain major obstacles. In this study, a highly dispersed PtNi alloy@Zr-doped 3D hollow flower-like MgAl2O4 (AMO) spheres was prepared through a hydrophobic driving strategy. During a 50-hour test at 550°C, the catalyst exhibited no significant decline in CH4 and CO2 conversion rates, demonstrating its excellent anti-sintering and anti-coking performance. The unique anti-coking performance can be attributed to Zr-induced oxygen vacancies, which enhance oxygen mobility and reduce carbon deposition. Besides, doped Zr increases basic active sites, enhancing CO2 adsorption and activation, thus accelerating carbon species conversion. At 700°C, the unique synergy between highly dispersed Pt and Ni enabled CH4 and CO2 conversion rates to reach 67.5% and 73.8%, respectively. The incorporation of Pt or Zr extends the Ni-Ni bond and partially coordinates with Ni, enhancing the stability of the Ni lattice. The reaction of CH4 and CO2 follows the Langmuir-Hinshelwood (L-H) mechanism, where both reactant molecules are adsorbed and activated on the metallic sites. Moreover, the effective energy barrier for the CH oxidation pathway is lower by 0.16eV than that for the C oxidation pathway, which helps suppress the formation of carbon deposits.

In Situ Modulated Nickel Single Atoms on Bicontinuous Porous Carbon Fibers and Sheets Networks for Acidic CO2 Reduction.

Carbon-supported single-atom catalysts exhibit exceptional properties in acidic CO2 reduction. However, traditional carbon supports fall short in building high-site-utilization and CO2-rich interfacial environments, and the structural evolution of single-atom metals and catalytic mechanisms under realistic conditions remain ambiguous. Herein, an interconnected mesoporous carbon nanofiber and carbon nanosheet network (IPCF@CS) is reported, derived from microphase-separated block copolymer, to improve catalytic efficiency of isolated Ni. In IPCF@CS nanostructure, highly mesoporous IPCF hinders stacking of CS that provides additional fully exposed sites and abundant bicontinuous mesochannels of IPCF facilitate smooth CO2 transport. Such unique features enable enhanced Ni utilization and local CO2 enrichment, which cannot be achieved over conventional pore-deficient and discontinuous porous carbon fibers-based supports. In situ X-ray and Infrared spectroscopy coupling constant-potential calculations reveal the dynamic distortion of the planar Ni-N4 to an out-of-plane configuration with expanded Ni-N bond during operating CO2 electroreduction. The potential-driven low-valance-state Ni-N4 possesses enhanced intrinsic electrokinetics for CO2 activation and CO desorption yet inhibiting hydrogen evolution. The favorable electronic and interfacial reaction environments, resulted from the in situ tailored Ni site and IPCF@CS support, achieve an FE of near 100% at 540mAcm-2, a TOF of 55.5 s-1, and a SPCE of 89.2% in acidic CO2-to-CO electrolysis.

Crystal structure of bis-{5-(4-chloro-phen-yl)-3-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-1H-1,2,4-triazol-1-ido}nickel(II) methanol disolvate.

The unit cell of the title compound, [Ni(C16H10ClN6)2]·2CH3OH, consists of a neutral complex and two methanol mol-ecules. In the complex, the two tridentate 2-(3-(4-chloro-phen-yl)-1H-1,2,4-triazol-5-yl)-6-(1H-pyrazol-1-yl)pyridine ligands coordinate to the central NiII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octa-hedral coordination sphere. Neighbouring tapered mol-ecules are linked through weak C-H(pz)⋯π(ph) inter-actions into monoperiodic chains, which are further linked through weak C-H⋯N/C inter-actions into diperiodic layers. The inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H⋯H 32.8%, C⋯H/H⋯C 27.5%, N⋯H/H⋯N 15.1%, and Cl⋯H/H⋯Cl 14.0%. The average Ni-N bond distance is 2.095 Å. Energy framework analysis at the HF/3-21 G theory level was performed to qu-antify the inter-action energies in the crystal structure.

Unveiling the Aggregation of M-N-C Single Atoms into Highly Efficient MOOH Nanoclusters during Alkaline Water Oxidation.

M-N-C-type single-atom catalysts (SACs) are highly efficient for the electrocatalytic oxygen evolution reaction (OER). And the isolated metal atoms are usually considered real active sites. However, the oxidative structural evolution of coordinated N during the OER will probably damage the structure of M-N-C, hence resulting in a completely different reaction mechanism. Here, we reveal the aggregation of M-N-C materials during the alkaline OER. Taking Ni-N-C as an example, multiple characterizations show that the coordinated N on the surface of Ni-N-C is almost completely dissolved in the form of NO3 -, accompanied by the generation of abundant O functional groups on the surface of the carbon support. Accordingly, the Ni-N bonds are broken. Through a dissolution-redeposition mechanism and further oxidation, the isolated Ni atoms are finally converted to NiOOH nanoclusters supported by carbon as the real active sites for the enhanced OER. Fe-N-C and Co-N-C also have similar aggregation mechanism. Our findings provide unique insight into the structural evolution and activity origin of M-N-C-based catalysts under electrooxidative conditions.

Di-chloridotetra-kis-(3-meth-oxy-aniline)nickel(II).

The reaction of nickel(II) chloride with 3-meth-oxy-aniline yielded di-chlorido-tetra-kis-(3-meth-oxy-aniline)nickel(II), [NiCl2(C7H9NO)4], as yellow crystals. The NiII ion is pseudo-octa-hedral with the chloride ions trans to each other. The four 3-meth-oxy-aniline ligands differ primarily due to different conformations about the Ni-N bond, which also affect the hydrogen bonding. Inter-molecular N-H⋯ Cl hydrogen bonds and short Cl⋯Cl contacts between mol-ecules link them into chains parallel to the b axis.

Bis[S-octyl 3-(2-methyl-propyl-idene)di-thio-carb-az-ato-κ2N3,S]nickel(II).

The central NiII atom in the title complex, [Ni(C13H25N2S2)2], is located on an inversion center and adopts a roughly square-planar coordination environment defined by two chelating N,S donor sets of two symmetry-related ligands in a trans configuration. The Ni-N and Ni-S bond lenghts are 1.9193 (14) and 2.1788 (5) Å, respectively, with a chelating N-Ni-S bond angle of 86.05 (4)°. These data are compared with those measured for similar di-thio-carbazato ligands that bear n-octyl or n-hexyl alkyl chains. Slight differences are observed with respect to the phenyl-ethyl-idene derivative where the ligands are bound cis relative to one another.

Unraveling Meso-Substituent Steric Effects on the Mechanism of Hydrogen Evolution Reaction in NiII Porphyrin Hydrides Using DFT Method.

Substituents at the meso-site of metalloporphyrins profoundly influence the hydrogen evolution reaction (HER) mechanism. This study employs density functional theory (DFT) to computationally analyze NiII-porphyrin and its hydrides derived from tetrakis(pentafluorophenyl)porphyrin molecules, presenting stereoisomers in ortho- or para-positions. The results reveal that the spatial resistance effect of meso-substituted groups at the ortho- and para-positions induces significant changes in Ni-N bond lengths, angles, and reaction dynamics. For ortho-position substituents forming complex I, a favorable 88.88 ų spherical space was created, facilitating proton coordination and the formation of H2 molecules; conversely, para-position substituents forming complex II impeded H2 formation until bimolecular complexes arose. Molecular dynamics (MD) analysis and comparison were conducted on the intermediation products of I-H2 and (II-H)2, focusing on the configuration and energy changes. In the I-H2 products, H2 molecules underwent separation after 150 fs and overcame the 2.2 eV energy barrier. Subsequently, significant alterations in the spatial structure were observed as complex I deformed. In the case of (II-H)2, it was influenced by the distinctive "sandwich" configuration; the spatial structure necessitated overcoming a 6.7 eV energy barrier for H2 detachment and a process observed after 2400 fs.

Microenvironment reconstitution of highly active Ni single atoms on oxygen-incorporated Mo2C for water splitting

The rational design of efficient bifunctional single-atom electrocatalysts for industrial water splitting and the comprehensive understanding of its complex catalytic mechanisms remain challenging. Here, we report a Ni single atoms supported on oxygen-incorporated Mo2C via Ni-O-Mo bridge bonds, that gives high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) bifunctional activity. By ex situ synchrotron X-ray absorption spectroscopy and electron microscopy, we found that after HER, the coordination number and bond lengths of Ni-O and Ni-Mo (Ni-O-Mo) were all altered, yet the Ni species still remain atomically dispersed. In contrast, after OER, the atomically dispersed Ni were agglomerated into very small clusters with new Ni-Ni (Ni-O-Ni) bonds appeared. Combining experimental results and DFT calculations, we infer the oxidation degree of Mo2C and the configuration of single-atom Ni are both vital for HER or OER. This study provides both a feasible strategy and model to rational design highly efficient electrocatalysts for water electrolysis.

Unusual Ni⋯Ni interaction in Ni(ii) complexes as potential inhibitors for the development of new anti-SARS-CoV-2 Omicron drugs.

Two nickel(ii) coordination complexes [Ni(L)]2(1) and [Ni(L)]n(2) of a tetradentate Schiff base ligand (H2L) derived from 2-hydroxy-1-naphthaldehyde with ethylenediamine were synthesized, designed, and characterized via spectroscopic and single crystal XRD analyses. Both nickel(ii) complexes exhibited unusual Ni⋯Ni interactions and were fully characterized via single-crystal X-ray crystallography. Nickel(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) crystallize in monoclinic and triclinic crystal systems with P21/c and P1̄ space groups, respectively, and revealed square planar geometry around each Ni(ii) ion. The structure of both the complexes have established the existence of a new kind of metal system containing nickel(ii)-nickel(ii) interactions with a square planar-like geometry about the nickel(ii) atoms. Both square planar Ni(ii) complexes were often stacked with relatively short Ni⋯Ni distances. The non-bonded Ni-Ni distance (Ni⋯Ni separation) seems to be 3.356 Å and 3.214 Å from the nickel atoms of [Ni(L)]2(1) and [Ni(L)]n(2), respectively. These distances are shorter than the sum of their van der Waals radii (4.80 Å) but longer than the sum of their covalent radii (2.50 Å), indicating that there is a Ni⋯Ni interaction but not a Ni-Ni bond. The discrete molecules are π-stacked and connected via weak intermolecular interactions (C-H⋯O and C-H⋯N). Cyclic voltammetry measurements were obtained for both the complexes, and their pharmacokinetic and chemoinformatics properties were also explored. Detailed structural analysis and non-covalent supramolecular interactions were investigated using single-crystal structure analysis and computational approaches. Both the unique structures show good inhibition performance for the Omicron spike proteins of the SARS CoV-2 virus. To gain insights into potential SARS-CoV-2 Omicron drugs and find inhibitors against the Omicron variants of SARS-CoV-2, we examined the molecular docking of the nickel(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) with the SARS-CoV-2 Omicron spike protein (PDB ID: 7WK2 and 7WVO). A strong binding was predicted between Ni(ii) coordination complexes [Ni(L)]2(1) and [Ni(L)]n(2) with the SARS-CoV-2 Omicron variant receptor protein through the negative value of binding affinity. Molecular docking of Nil(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) with a DNA duplex (PDB ID: 7D3T) and RNA (PDB ID: 7TDC) binding protein was also studied. Overall, this study suggests that Ni(ii) complexes can be considered as drug candidates against the Omicron variants of SARS-CoV-2.

Data-driven stabilization of NimPdn-m nanoalloys: a study using density functional theory and data mining approaches.

Green hydrogen, generated through the electrolysis of water, is a viable alternative to fossil fuels, although its adoption is hindered by the high costs associated with the catalysts. Among a wide variety of potential materials, binary nickel-palladium (NiPd) systems have garnered significant attention, particularly at the nanoscale, for their efficacious roles in catalyzing hydrogen and oxygen evolution reactions. However, our atom-level understanding of the descriptors that drive their energetic stability at the nanoscale remains largely incomplete. Here, we investigate by density functional theory calculations the descriptors that drives the stability of the NimPdn-m clusters for different sizes (n = 13, 27, 41) and compositions. To achieve our goals, a large number of trial configurations were generated and selected using data mining algorithms (k-means, t-SNE) and genetic algorithms, while the most important physical-chemical descriptors were identified using Spearman correlation analysis. We have found that core-shell formation, with the smaller Ni atoms lying in the center of the particle, plays a major role in the stabilization of the nanoalloys, and this effect causes the alloys to assume a icosahedral-fragment configuration (as the unary nickel cluster) instead of a fcc fragment (as the unary palladium cluster). However, the core-shell formation in this alloy is unique in that Pd poor compositions exhibit scattered Pd atoms on the surface. As the palladium content increases, this gives rise to the complete Pd shell. This stabilization mechanism is quantitatively supported by the different correlations observed in the number of Ni-Ni and Pd-Pd bonds with energy, in which the latter tends to decrease alloy stability. Furthermore, a notable trend is the correlation between the coordination number of Ni atoms with alloy stabilization, while the coordination of Pd atoms shows an inverse correlation.

Six-coordinated nickel(II) complexes with benzothiadiazole Schiff-base ligands: synthesis, crystal structure, magnetic and HFEPR study.

Two new nickel(II) complexes, namely Ni(L1)2 (1) and Ni(L2)2·CH2Cl2(2) were obtained by reacting nickel(II) acetate tetrahydrate with the benzothiadiazole Schiff base ligands HL1 = 2-[4-(2,1,3-benzothiadiazole)imino]methyl-phenol or HL2 = 2-[(2,1,3-benzothiadiazol-4-ylimino)methyl]-6-methoxyphenol in the presence of Et3N. The tridentate NNO chelate ligands induce a distorted octahedral environment around the nickel(II) ions. Single crystal X-ray diffraction analysis reveals elongated Ni-N bonds with the nitrogen atom of the benzothiadiazole ring in both complexes. Intermolecular hydrogen bonds and π-π stacking interactions create two-dimensional and three-dimensional supramolecular arrays, respectively, for complexes 1 and 2. Magnetic susceptibility and high-field electron paramagnetic resonance measurements show the presence of significant magnetic anisotropy, with an axial distortion parameter D of -8--10 cm-1.

Fe acting as functionalized auxiliary agents in nitrogen-doped carbon supported Ni-based catalysts for electrocatalytic CO2 Reduction: Effect of valence state

Converting CO2 into useful chemicals is an effective measure to address the energy crisis and the greenhouse effect. CO2RR has become a research hotspot due to its mild conditions. Ni-N-C catalysts are known as promising electrocatalysts, while achieving atomic level dispersion of Ni on the surface of the carrier is still facing challenges. In this work, various N-doped carbon supported Ni-based catalysts were synthesized by selecting Fe2+/Fe3+ as functionalized auxiliary agents in precursors. Different coordination situations of Fe(III)/Ni@NC and Fe(II)/Ni@NC are formed which derived from the valence state of Fe. During the synthesis process of Fe(III)/Ni@NC, Ni2+ replaced Fe3+ through competitive complexation, thereby achieving atomic level dispersion of Ni atoms on the catalyst surface. XAS confirms that Fe(III)/Ni@NC is a Ni-single-atom catalyst with Ni-N4 coordination. In contrast, Fe(II)/Ni@NC contains Ni3C/Ni nanoparticles coated with carbon layer, which shows a characteristic peak approaching to 2.12 Å related to the metallic Ni-Ni bonds. In the H-type cell, the FECO of Fe(III)/Ni@NC achieves 97.8 % at −0.83 V and maintains over 95 % in a wide potential window. The in-situ Fourier transform infrared (FTIR) spectroscopy confirms that the excellent product CO selectivity in CO2RR is due to the accumulation of *COOH intermediates at the active sites. Significantly, Fe(III)/Ni@NC shows excellent performance in the flow cell with FECO over 96 % from −40 to −140 mA cm−2. This work reveals the impact of Fe valence state of functionalized auxiliary agents on the electrocatalytic performance of materials, which provides a new approach for designing high-performance atomically dispersed electrocatalysts.

Jahn-Teller distortion in bis(terpyridine)nickel(III) – Elongation or compression?

DFT methods were used to evaluate the type of Jahn-Teller distortion in the low spin d7 bis(terpyridine)nickel(III) doublet. The strain of the tridentate terpyridine ligand in bis(terpyridine)nickel(III) leads to longer Ni(III)-N terminal bond lengths than the Ni(III)-N central bonds. In addition, in all DFT optimized bis(terpyridine)nickel(III) molecules, the one set of Ni(III)-N terminal bonds are longer than the other set of Ni(III)-N terminal bonds. Three pairs of Ni(III)-N bonds are present in bis(terpyridine)nickel(III), namely 2 longer Ni(III)-Nterminal1 terminal bonds, 2 medium length Ni(III)-Nterminal2 terminal bonds and 2 shorter Ni(III)-Ncentral central bonds, similar to orthorhombic Jahn-Teller distortion in octahedral complexes. Evaluation of bond length differences, contraction of bonds, spin density plots and the character of the singly occupied molecular orbital (SOMO) and singly unoccupied molecular orbital (SUMO), led to a set of criteria to consider in evaluating the type of Jahn-Teller distortion in the low spin d7 bis(terpyridine)nickel(III) doublet. Jahn-Teller distortion can lead to elongation (z-out) or compression (z-in) of a pair of opposite Ni-N bonds. One key criteria found, is, if the difference in bond length between Ni(III)-Nterminal1 and Ni(III)-Nterminal2 is smaller than the difference in bond length of Ni(III)-Nterminal2 and Ni(III)-Ncentral, then it is a Jahn-Teller compression geometry (and vice versa for a Jahn-Teller elongation geometry).

Stabilization of NCM811 cathode for Li-ion batteries by N-doped carbon coating

Ternary nickel-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM811), as a promising next-generation cathode material for lithium-ion batteries, is still suffered from severe capacity fading triggered by irreversible phase transition and side reactions during cycling, which can be effectively circumvented by surface coating. Herein, microspheric NCM811 particles are homogeneously coated by N-doped carbon layer via a facile and low-cost rheological phase reaction method followed by low temperature sintering. The N-doped carbon coating disperses more uniformly than carbon coating on NCM811, which is attributed to the formation of NiN bond between carbon coating layer and bulk NCM811. And the introduced N element can inhibit the reduction of Ni3+ to Ni2+ on the surface of NCM811, leading to a positive effect on the suppression of cationic mixing that further improves the structural stability. Based on the electrochemical performance analyses, it is found that the surface pseudocapacitance and Li+ diffusion ability both are significantly promoted after N-doped carbon coating. Benefit from the suitable pseudocapacitive behavior and high Li+ diffusion coefficient, the NCM811-CN0.5 electrode presents a discharge specific capacity of 216.98 mAh/g at 0.1C, 151.01 mAh/g at 10C, and capacity retention of 82.3 % after 500 cycles at 5C, indicating that it will be an ideal cathode material for developing high-power and long-lifespan lithium-ion batteries.

Field-Induced Single-Ion Magnet Behavior in Nickel(II) Complexes with Functionalized 2,2':6'-2″-Terpyridine Derivatives: Preparation and Magneto-Structural Study.

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4'-carboxyl-2,2':6',2″-terpyridine and terpyepy = 4'-[(2-pyridin-4-yl)ethynyl]-2,2':6',2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel-nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9-200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to -6.0 (1) and -4.7 cm-1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0-5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

Facile low-temperature supercritical carbonization method to prepare high-loading nickel single atom catalysts for efficient photodegradation of tetracycline

Environmental photocatalysis is a promising technology for treating antibiotics in wastewater. In this study, a supercritical carbonization method was developed to synthesize a single-atom photocatalyst with a high loading of Ni (above 5 wt.%) anchored on a carbon-nitrogen-silicate substrate for the efficient photodegradation of a ubiquitous environmental contaminant of tetracycline (TC). The photocatalyst was prepared from an easily obtained metal-biopolymer-inorganic supramolecular hydrogel, followed by supercritical drying and carbonization treatment. The low-temperature (300°C) supercritical ethanol treatment prevents the excessive structural degradation of hydrogel and greatly reduces the metal clustering and aggregation, which contributed to the high Ni loading. Atomic characterizations confirmed that Ni was present at isolated sites and stabilized by Ni-N and Ni-O bonds in a Ni-(N/O)6C/SiC configuration. A 5% Ni-C-Si catalyst, which performed the best among the studied catalysts, exhibited a wide visible light response with a narrow bandgap of 1.45 eV that could efficiently and repeatedly catalyze the oxidation of TC with a conversion rate of almost 100% within 40 min. The reactive species trapping experiments and electron spin resonance (ESR) tests demonstrated that the h+, and ·O2− were mainly responsible for TC degradation. The TC degradation mechanism and possible reaction pathways were provided also. Overall, this study proposed a novel strategy to synthesize a high metal loading single-atom photocatalyst that can efficiently remove TC with high concentrations, and this strategy might be extended for synthesis of other carbon-based single-atom catalysts with valuable properties.

Structures of nickel chloride and thiolate complexes supported by PCN and POCOP pincer ligands and catalytic reactivity of the chloride complexes.

Nickel chloride and thiolate complexes supported by benzene-pyridine-based nonsymmetrical PCN pincer ligands, [2-(tBu2PO)-6-(2-pyrindinyl-4-R)-C6H3]NiX (R = H, CH3, CF3; X = Cl, SH, SPh), were synthesized and fully characterized. The structures of these complexes and the catalytic reactivity of the chloride complexes were investigated along with the related POCOP counterparts [2,6-(tBu2PO)2C6H3]NiX (X = Cl, SH). It was found that the composition and substitution of the pincer backbone evidently influence the structures and catalytic reactivity. The Ni-P and Ni-Cipso bond lengths in the PCN complexes are significantly shorter than those in the POCOP complex. The Ni-Cl and Ni-S bond lengths in the PCN complexes are longer than those in the POCOP complexes. An electron rich pyrindinyl ring in the PCN complexes makes the Ni-Cl bond longer. The Ni-N bond length is more sensitive to the auxiliary ligand compared with the Ni-P bond length in the PCN complexes. The PCN chloride complexes were found to be active catalysts for selective hydration of nitriles to primary amides in the presence of NaOH at 80 °C and the catalytic activity increases with the increase of electron richness of the pyridinyl ring. However, the corresponding POCOP counterpart is inactive under the same conditions.

SYNTHEZIS AND STRUCTURAL INVESTIGATION OF bis-(PYRAZIN 2-CARBOXYLATE)-Ni(II)-DIHIDRATE

A new Ni (II) C pyrazine 2-carboxylic acid complex was synthesized. Single crystals were obtained for X-ray diffraction analysis and the crystal and molecular structures of the new complex were deciphered. The crystallographic parameters of complex compounds are as follows: Molecular formula is C10H10N4NiO6, Molecular weight is 340.91 k.v.; temperature during measurement is 100.0 (2) K; Absorption frequency is MoKα = 0.71073E, Syngonia – Monoclinic; space group is P21 /c, Crystal lattice parameters are: a = 5.2136Å, b = 11.10073Å, c = 10.15267Å; β = 100.14620C, volume of the crystal lattice is V = 578.395Å3, number of molecules in the crystal lattice is Z = 2, density is d = 1,956 g / cm3, absorption coefficient is 1,715 mm-1, dimensions of the single crystal are 0.20x0.18x0,15 mm3; range of teta is 3.670–30.6100C; The boundaries of the hkl planes in the crystal section are h = -7+7 k = -15 +15.l = -14+14 the total number of collected reflexes is 8546, the number of independent reflexes is 1727, the boundary of the transitions is 0.761 and 0.707. Total Rfactor = 0.0240. It has been found that the central Ni(II) atom is coordinated by one oxygen atom of the carboxyl group and a donor nitrogen atom of the pyrazine ring, forming five-membered stable bonds. Two water molecules are coordinated by the Ni(II) atom and complete the coordination number of the metal to six. The Ni–O bond distance is 2.0874 Å, the Ni-N bond distance is 2.0864 Å. The second oxygen atom is not coordinated by the Ni(II) atom and forms a strong hydrogen bond with coordinated water molecules

Transition Metal Doped-Chalcogenide Based Electrocatalysts for Oxygen Evolution Reaction

Hydrogen, which possesses high gravimetric energy density, has recently received great attentions to respond to the seriousness of global climate change [1, 2]. In particular, the alkaline water electrolysis cells (AECs) that can produce hydrogen through electrochemical reactions without greenhouse gas emissions are substantially promising as renewable next-generation energy storage and conversion devices. In AECs, oxygen evolution reactions (OERs) occur at the anode, while hydrogen evolution reactions take place at the cathode [3, 4]. However, the sluggish kinetics of the multi-electron transfer process is a paramount challenge for efficient OER activity. Furthermore, precious metal catalysts such as iridium and ruthenium are still mainly used as an OER catalyst, and their low economic efficiency and durability are acting as major problems in the commercialization stage. Therefore, the reduction of reaction overpotential is crucial to boost catalytic efficiency for OER in AECs. In this study, the OER catalyst study is performed on sulfide-based chalcogenide materials. It has been reported that the sulfide-based chalcogenide materials have shown the excellent catalytic activity because the covalent characteristics between transition metal and chalcogenide is stronger than that of oxide-based catalysts [5]. In particular, among various sulfide-based chalcogenide materials, nickel sulfide-based catalysts have actively studied because they can simply synthesize using a hydrothermal method. Additionally, nickel sulfides have a structurally Ni-Ni metal bond that makes it easy to transfer charge species for OERs. Herein, various transition metals are doped into the nickel sulfide to improve the catalytic activity and electrical conductivity via generation of extra defects in the crystal structure. The crystal structure and catalytic activity of chalcogenide catalysts are analyzed through various physicochemical and electrochemical analysis methods.