Mononuclear Nickel Research Articles

Chemical assessment of three octahedral Ni(II) complexes with heterocyclic acylpyrazolone ligand: Crystal structure, DFT-NBO analysis, Hirshfeld and Magnetic study

We have synthesized three novel mononuclear Nickel(II) coordination complexes [Ni(DMBPTMP)2(EtOH)2], [Ni(PCBPMP)2(DMF)(H2O)] and [Ni(PCBPTMP)2(DMSO)2] with σ-donating acylpyarazolone ligands. All the complexes have been comprehensively characterized via FTIR, UV–Vis, TGA, and Magnetic study. Additionally, single crystal X-ray diffraction analysis was successfully used to characterize the three complexes. The findings showed that the geometry around Ni(II) is slightly distorted octahedral in [Ni(DMBPTMP)2(EtOH)2], [Ni(PCBPMP)2(DMF)(H2O)] complexes and also in the centrosymmetric [Ni(PCBPTMP)2(DMSO)2] complex. In all the complexes the metal is bischelated by two pyrazolone molecules via carbonyl and benzoyl carbonyl oxygen donors, but with a different configuration of ligands. In addition to the experimental studies and spectroscopic characteristics, DFT computational analysis and Natural bonding orbital (NBO) analysis have been performed using a B3LYP/LANL2DZ basis set for the optimization. All three Ni(II) complexes give three distinct absorption transitions which has been proved by Electronic spectral analysis. A paramagnetic nature of the complex is confirmed through magnetic study. Utilising Hirshfeld surface analysis, intermolecular interactions of complexes were evaluated.

Mononuclear nickel(II) and copper(II) coordination compounds with ligands based on acetyl(benzoyl)acetone S-methylisothiosemicarbazones and 8-quinolinecarboxaldehyde. Synthesis and crystal structure

Template condensation of S-methylisothiosemicarbazones of acetyl- or benzoylacetone with 8-quinolinecarboxaldehyde in the presence of nickel(II) and copper(II) ions gave four new mononuclear coordination compounds [NiL1]I (I), [CuL1I] (II), [NiL2]I (III) и [CuL2I] (IV). The chemical composition of the products was confirmed by elemental analysis, IR spectroscopy, and mass spectrometry, and the crystal structure of compounds I and II was determined by X-ray diffraction analysis (CCDC no. 2266386, 2266387). X-ray diffraction study revealed a square planar coordination environment of the central ion of the cationic Ni(II) complex and square pyramidal geometry for the molecular Cu(II) complex.

Synthesis, Crystal Structures and Antibacterial Activity of Nickel(II), Cadmium(II) and Zinc(II) Complexes with Hydrazone Ligands.

Three mononuclear nickel(II), cadmium(II) and zinc(II) complexes, [NiL2]·2CH3OH·H2O (1), [CdI2(HL)]·CH3OH (2) and [ZnL2] (3), have been synthesized from 3-hydroxy-4-methoxy-N'-[(Z)-(pyridin-2-yl)methylidene]benzohydrazide (HL) by microwave irradiation method. All complexes were characterized by CHN elemental analyses and infrared spectra. Structures of the complexes were further studied by single crystal X-ray determination, which reveals that the Ni and Zn atoms in complexes 1 and 3 are in octahedral coordination, and the Cd atom in complex 2 is in square pyramidal coordination. The biological activity of the complexes on the bacterial strains Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli wasevaluated. As a result, the zinc complex has interesting antibacterial activities.

Mononuclear Nickel(II) and Copper(II) Coordination Compounds with Ligands Based on Acetyl(benzoyl)acetone S-Methylisothiosemicarbazones and 8-Quinolinecarboxaldehyde. Synthesis and Crystal Structure

Mononuclear Nickel(II) and Copper(II) Coordination Compounds with Ligands Based on Acetyl(benzoyl)acetone S-Methylisothiosemicarbazones and 8-Quinolinecarboxaldehyde. Synthesis and Crystal Structure

Shift of the reduction potential of nickel(II) Schiff base complexes in the presence of redox innocent metal ions.

With the objective of gaining insight into the modulation of the reduction potential of the Ni(II/I) couple, we have synthesized two mononuclear nickel(II) complexes, NiLen (H2Len = N,N'-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane) and NiLpn (H2Lpn = N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane) of two N2O4 donor ligands and recorded their cyclic voltammograms. Both the nickel complexes show reversible reduction processes for the Ni(II/I) couple in acetonitrile solution but the reduction potential of NiLpn (E1/2 = -1.883 V) is 188 mV more positive than that of NiLen (E1/2 = -2.071 V). In the presence of redox inactive metal ions (Li+, Na+, K+, Mg2+, Ca2+ and Ba2+), the reduction potentials are shifted by 49-331 mV and 99-435 mV towards positive values compared to NiLen and NiLpn, respectively. The shift increases with the decrease of the pKa of the respective aqua-complexes of the metal ion but is poorly co-linear; however, better linearity is found when the shift of the mono- and bi-positive metal ion aqua complexes is plotted separately. Spectrophotometric titrations of these two nickel complexes with the guest metal ions in acetonitrile showed a well-anchored isosbestic point in all cases, confirming the adduct formation of NiLen and NiLpn with the metal ions. Structural analysis of single crystals, [(NiLen)Li(H2O)2]·ClO4 (1), [(NiLpn)Li(H2O)]·ClO4 (2), [(NiLpn)2Na]·BF4 (3) and [(NiLpn)2Ba(H2O)(ClO4)]·ClO4 (4), also corroborates the heterometallic adduct formation. The orbital energies of the optimised heterometallic adducts from which electron transfers originated were calculated in order to explain the observed reduction process. A strong linear connection between the calculated orbital energies and the experimental E1/2 values was observed. According to MEP and 2D vector field plots, the largest shift for divalent metal ions is most likely caused by the local electric field that they impose in addition to Lewis acidity.

IMPACT OF METAL SALTS ON COORDINATION CHEMISTRY OF NICKEL(II) WITH A N3O DONOR SCHIFF BASE LIGAND: SYNTHESIS, STRUCTURES AND HERSHFIELD SURFACE ANALYSIS

The key findings and significance of this report is the synthesis and characterization of two mononuclear nickel(II) complexes, [Ni(L)(val)].0.5MeOH (1) and [Ni(HL)2](ClO4)2 (2) derived from a tetradentate Schiff base ligand HL and two different nickel(II) salts. These complexes were thoroughly characterized using techniques such as elemental analysis, IR spectroscopy, single crystal X-ray diffraction, and Hirshfeld surface analysis. The results revealed distinct coordination modes of the ligands in the complexes, leading to different non-covalent interactions and packing arrangements in their crystal structures. Specifically, complex 1 exhibited tetradentate coordination in addition to the bidentate o-vanillinate ligand, while complex 2 featured tridentate coordination with the zwitterionic form of the ligand. Hirshfeld surface analysis provided insights into the relative contributions of various intermolecular interactions, highlighting the significance of hydrogen bonding, tetrel bonding, and other non-covalent interactions in stabilizing the crystal structures. In general, this study contributes to the differences in structural integrity on slide variation in metal salts and the understanding in depth of various non covalent interactions using Hirshfeld surface analysis tool.

Design of Azomethine based Metalloorganic Complexes and their Binding Interactions with Nucleic Acid and Protein

Mononuclear nickel, copper, and zinc complexes based on salen type (ONNO) donor acting as a tetradentate ligand obtained by the condensation of 4-methyl-o-phenylenediamine and 5-fluoro salicylaldehyde in 1:2 ratios. The compounds are characterized using UV-visible, FT-IR, 1H, 13C-NMR, HR-MS, Elemental (CHN) analyses ESR spectral techniques, and single crystal X-ray diffraction studies (SC-XRD). The binding interactions of the metal complexes with deoxyribonucleic acid (DNA) and bovine serum albumin (BSA) are monitored using UV absorption titration and tryptophan emission quenching techniques, respectively. The complexes possess strong binding propensities with DNA and prefer groove binding, as indicated by the hyperchromic effect. The complexes quench the intrinsic fluorescence of BSA with increasing amounts of the complex concentration in a dose-dependent manner. The gel electrophoresis was carried out against pBR322 to analyze the cleaving ability of the complexes. The results of the NBO (natural bond orbitals) analysis performed in combination with the Time-dependent Density Functional Theory (TD-DFT) calculations provided a good explanation of their electronic and structural characteristics. Further, the predictions of molecular docking studies support the experimental observations. The Gel electrophoresis study reveals the cleaving ability of the complexes by their interactions with DNA. In addition, the cell viability of the complexes is assessed based on MTT assay and the results indicate that they have a good antiproliferative activity only on liver cancer cell-line HepG-2 and does not show cytotoxic effect on normal vero cell lines with 90% viability.

Copper(II) and Nickel(II) Complexes Derived from Isostructural Bromo- and Fluoro-Containing Bis-Schiff Bases: Syntheses, Crystal Structures and Antimicrobial Activity.

A mononuclear copper(II) complex [CuLa] (1), and three mononuclear nickel(II) complexes [NiLa] (2), [NiLa]·CH3OH (2·CH3OH) and [NiLb] (3), where La and Lb are the dianionic form of N,N'-bis(4-bromosalicylidene)-1,2-cyclohexanediamine (H2La) and N,N'-bis(4-fluorosalicylidene)-1,2-cyclohexanediamine (H2Lb), respectively, were prepared and structurally characterized by spectroscopy method and elemental analyses. The detailed structures were determined by X-ray single crystal diffraction. All the copper and nickel complexes are mononuclear compounds. The metal ions in the complexes are in square planar coordination, with the two phenolate oxygens and two imine nitrogens of the Schiff base ligands. The biological effect of the four complexes were assayed on the bacteria strains Staphylococcus aureus, Escherichia coli and Candida albicans.

A novel nickel(II) complex with N,S donor Schiff base: Structural characterisation, DFT, TD-DFT study and catalytic investigation.

One new mononuclear nickel(II) thiosemicarbazone complex (1), has been synthesised from the Schiff base ligand derived from p-anisaldehyde and thiosemicarbazide. Complex 1 is characterized by using different spectroscopic techniques and single crystal X-ray structure analysis. Time dependent density functional theory (TD-DFT) was performed to simulate the electronic spectra of the complex 1 with the help of Polarizable Continuum Model (PCM) model. Complex 1 acts as functional models. The catalytic property has been evaluated from Lineweaver-Burk plot using the Michaelis-Menten approach of enzyme catalysis with a kcat value of the order of 708 h-1.

Synthesis and Characterization of a Mononuclear Nickel (II) Complex: Its Dual Electrocatalytic Performance towards Hydrogen Evolution Reaction and Hydrazine Oxidation

AbstractThere is high demand of clean and sustainable energy where hydrogen can be an alternative instead of fossil fuel. We report here synthesis, characterization and applications of a mononuclear Ni(II) complex, [Ni(L)2] (1), with a salen type ligand, 2,2′‐((1E,1′E)‐(propane‐1,2‐diylbis(azanylylidene))bis(methanylylidene))bis(4‐bromophenol) (H2L). It has been obtained by a mild reaction with high yield. It has been characterized by the standard analytical techniques. Complex 1 has been used as an electrocatalyst in hydrogen evolution reaction where acetic acid is used as a proton source in DMF with a TOF value of 182.11 s−1. Various control experiments and results suggest the relevance of Complex 1 as the efficient electrocatalyst in the hydrogen generation from acetic acid. The metal complex has been deposited on a glassy carbon electrode and used efficiently in electrocatalytic oxidation of hydrazine.

Switch in Selectivities by Dinuclear Nickel Catalysis: 1,4-Hydroarylation of 1,3-Dienes to Z-Olefins.

One of the most challenging tasks in organic synthesis is to control selectivities, especially switching the well-known selectivity to obtain new isomers that were previously inaccessible. Inspired by biological catalysis involving multiple metal centers, catalysis enabled by binuclear metal complexes offers the potential to induce reactivity and selectivity that might not be available to mononuclear catalysts. Herein, we describe that using a macrocyclic bis pyridyl diimine dinickel complex as the catalyst, the commonly observed 4,3-regioselectivity of hydroarylation of 1,3-dienes is switched to 1,4-hydroarylation with thermodynamically less stable Z-stereoselectivity, offering challenging synthetic target Z-olefins. DFT calculations show that the activation of 1,3-diene proceeds through dinuclear Ni-diolefin coordination, and the synergistic effects of two Ni nuclei enable reactivity and selectivity of this binuclear catalysis substantially different from those of mononuclear nickel complexes in the current reaction.

Cover Feature: Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes (Eur. J. Inorg. Chem. 34/2023)

Cover Feature: Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes (Eur. J. Inorg. Chem. 34/2023)

Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes

AbstractWater splitting is a potential pathway for hydrogen gas evolution and thereby realization of a carbon‐neutral sustainable energy scheme. However, oxidation of water to dioxygen is the major impediment in conversion of solar energy to fuel. Herein, density functional studies are conducted to explore the reactivity conduits of two molecular electro‐catalysts consisting of nickel and copper tetra‐anionic tetradentate amide ligand complexes of the type [(L1)MII]2−, where L1=o‐phenylenebis(oxamidate), and their substitutionally modified analogues. While nickel complexes demonstrate complex borderline chemistry between homogeneous and heterogeneous pathways, showing competition between water oxidation and molecular species degradation, copper complexes display robust and efficient molecular water oxidation behavior. Our analysis predict that this disparity is primarily due to the reversible O−O bond formation in nickel complexes, which provide the platform necessary for a direct attack of OH−/H+ on the metal and terminally accessible amidate groups of the 2e− oxidized anionic intermediate, [(L1⋅)NiIII(OH)]1−, respectively. This intermediate streamline ligand deactivation with a comparatively higher driving force for nickel complexes in acidic medium. Contrarily, the copper complexes display radical character on the hydroxyl ligand in the corresponding intermediate, [(L1⋅)CuII(OH⋅)]1−, that expedite O−O interaction, leading to predominant homogeneous water oxidation under all conditions.

Mononuclear nickel(II) and dinuclear palladium(II) complexes of a redox-active iminophenolate-based O,O,N,N,S,S ligand – experimental and theoretical vision

“A new potentially hexadentate redox-active schiff base ligand, H2L = 2-((Z)-(2-(2-(2-((Z)-3,5-di‑tert‑butyl‑2-hydroxybenzylideneamino)phenylthio)ethylthio)phenylimino)methyl)-4,6-di‑tert-butylphenol, reacts with NiII(O2CCH3)2·4H2O and PdCl2 in CH3OH in the presence of air and Et3N affording isolation of yellow and red crystalline solids of composition [Ni(L)] (1) and [Pd2(L)Cl2].2CH2Cl2 (2), respectively. When examined by cyclic voltammetry (CV), 1 exhibits three quasireversible responses at E1/2 = 0.60 V (peak-to peak separation, ΔEp = 80 mV), 0.96 V (ΔEp = 80 mV) and 1.16 V (ΔEp = 160 mV) vs SCE (saturated calomel electrode); while 2 exhibits one quasireversible response at E1/2 = 1.185 V (peak-to peak separation, ΔEp = 130 mV). One electron oxidized species showed EPR spectrum correspond to ferromagnetically coupled system, S = 3/2 (S = 1 for NiII and S = ½ for phenoxyl radical). Structural analysis revealed that 1 is discrete mononuclear and 2 is discrete dinuclear coordination complex. In complex 1, each NiII is in distorted octahedral NiN2O2S2 environment where coordination is satisfied by two nitrogen atoms, two oxygen atoms and two sulfur atoms of the ligand. In complex 2, each Pd is in distorted square planner PdNOSCl environment where coordination is satisfied by one each nitrogen, oxygen and sulfur atoms of the ligand, and a chloride ion. DFT calculations at B3LYP-level of theory adequately describe the electronic structures of 1 and 2, containing a spin-unpaired d8 NiII ion and spin-paired d8 PdII ion. Time-dependent-DFT calculations on 1 and 2 shed light on the origin of UV−vis−NIR spectral absorptions.

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.

Mononuclear nickel and copper complexes as electrocatalyst for generation of hydrogen from acetic acid

Ever increasing use of conventional energy and demand of clean renewable energy inspire many researchers to produce effective systems for hydrogen generation. Herein we report two mononuclear complexes, [NiL] (Complex 1) and [CuL] (Complex 2), where H2L is 1,1′-(1E,1′E)-(propane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol, as electrocatalyst for hydrogen evolution reaction using acetic acid as the substrate. Both of the complexes have been synthesized under mild conditions and characterized by several methods. Single crystal X-ray structure of Complex 1 shows square planar geometry around nickel center. These complexes have effectively been used to reduce proton to generate hydrogen. Different control experiments have been carried out to understand the role of these catalysts and find their relevance in this regard. Turnover frequency (TOF) values for 1 and 2 have been determined as 653.1 and 777.5 s−1, respectively. Hydrogen is evolved via reduction of metal center followed by formation of metal hydride species.

Mononuclear nickel(ii)-flavonolate complexes of tetradentate tripodal 4N ligands as structural and functional models for quercetin 2,4-dioxygenase: structures, spectra, redox and dioxygenase activity.

Three new nickel(ii)-flavonolate complexes of the type [Ni(L)(fla)](ClO4) 1-3, where L is the tripodal 4N ligand tris(pyrid-2-ylmethyl)amine (tpa, L1) or (pyrid-2-ylmethyl)bis(6-methylpyrid-2-ylmethyl)amine (6-Me2-tpa, L2) or tris(N-Et-benzimidazol-2-ylmethyl)amine (Et-ntb, L3), have been isolated as functional models for Ni(ii)-containing quercetin 2,4-dioxygenase. Single crystal X-ray structures of 1 and 3 reveal that Ni(ii) is involved in π-back bonding with flavonolate (fla-), as evident from enhancement in C[double bond, length as m-dash]O bond length upon coordination [H(fla), 1.232(3); 1, 1.245(7); 3, 1.262(8) Å]. More asymmetric chelation of fla- in 3 than in 1 [Δd = (Ni-Ocarbonyl - Ni-Oenolate): 1, 0.126; 3, 0.182 Å] corresponds to lower π-delocalization in 3 with electron-releasing N-Et substituent. The optimized structures of 1-3 and their geometrical isomers have been computed by DFT methods. The HOMO and LUMO, both localized on Ni(ii)-bound fla-, are highly conjugated bonding π- and antibonding π*-orbitals respectively. They are located higher in energy than the Ni(ii)-based MOs (HOMO-1, dx2-y2; HOMO-2/6, dz2), revealing that the Ni(ii)-bound fla- rather than Ni(ii) would undergo oxidation upon exposure to dioxygen. The results of computational studies, in combination with spectral and electrochemical studies, support the involvement of redox-inactive Ni(ii) in π-back bonding with fla-, tuning the π-delocalization in fla- and hence its activation. Upon exposure to dioxygen, all the flavonolate adducts in DMF solution decompose to produce CO and depside, which then is hydrolyzed to give the corresponding acids at 70 °C. The highest rate of dioxygenase reactivity of 3 (kO2: 3 (29.10 ± 0.16) > 1 (16.67 ± 0.70) > 2 (1.81 ± 0.04 × 10-1 M-1 s-1)), determined by monitoring the disappearance of the LMCT band in the range 440-450 nm, is ascribed to the electron-releasing N-Et substituent on bzim ring, which decreases the π-delocalization in fla- and enhances its activation.

Effect of Redox-Inactive Metal Ion-Nickel(III) Interactions on the Redox Properties and Proton-Coupled Electron Transfer Reactivity.

Mononuclear nickel(II) and nickel(III) complexes of a bisamidate-bisalkoxide ligand, (NMe4)2[NiII(HMPAB)] (1) and (NMe4)[NiIII(HMPAB)] (2), respectively, have been synthesized and characterized by various spectroscopic techniques including X-ray crystallography. The reaction of redox-inactive metal ions (Mn+ = Ca2+, Mg2+, Zn2+, Y3+, and Sc3+) with 2 resulted in 2-Mn+ adducts, which was assessed by an array of spectroscopic techniques including X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and reactivity studies. The X-ray structure of Ca2+ coordinated to Ni(III) complexes, 2-Ca2+T, was determined and exhibited an average Ni-Ca distance of 3.1253 Å, close to the metal ions' covalent radius. XAS analysis of 2-Ca2+ and 2-Y3+ in solution further revealed an additional coordination to Ca and Y in the 2-Mn+ adducts with shortened Ni-M distances of 2.15 and 2.11 Å, respectively, implying direct bonding interactions between Ni and Lewis acids (LAs). Such a short interatomic distance between Ni(III) and M is unprecedented and was not observed before. EPR analysis of 2 and 2-Mn+ species, moreover, displayed rhombic signals with gav > 2.12 for all complexes, supporting the +III oxidation state of Ni. The NiIII/NiII redox potential of 2 and 2-Mn+ species was determined, and a plot of E1/2 of 2-Mn+ versus pKa of [M(H2O)n]m+ exhibited a linear relationship, implying that the NiIII/NiII potential of 2 can be tuned with different redox-inactive metal ions. Reactivity studies of 2 and 2-Mn+ with different 4-X-2,6-ditert-butylphenol (4-X-DTBP) and other phenol derivatives were performed, and based on kinetic studies, we propose the involvement of a proton-coupled electron transfer (PCET) pathway. Analysis of the reaction products after the reaction of 2 with 4-OMe-DTBP showed the formation of a Ni(II) complex (1a) where one of the alkoxide arms of the ligand is protonated. A pKa value of 24.2 was estimated for 1a. The reaction of 2-Mn+ species was examined with 4-OMe-DTBP, and it was observed that the k2 values of 2-Mn+ species increase by increasing the Lewis acidity of redox-inactive metal ions. However, the obtained k2 values for 2-Mn+ species are much lower compared to the k2 value for 2. Such a variation of PCET reactivity between 2 and 2-Mn+ species may be attributed to the interactions between Ni(III) and LAs. Our findings show the significance of the secondary coordination sphere effect on the PCET reactivity of Ni(III) complexes and furnish important insights into the reaction mechanism involving high-valent nickel species, which are frequently invoked as key intermediates in Ni-mediated enzymatic reactions, solar-fuel catalysis, and biomimetic/synthetic transformation reactions.

C-H Bond Activation by a Mononuclear Nickel(IV)-Nitrate Complex.

The recent focus on developing high-valent non-oxo-metal complexes for late transition metals has proven to be an effective strategy to study the rich chemistry of these high-valent species while bypassing the synthetic challenges of obtaining the oxo-metal counterparts. In our continuing work of exploring late transition metal complexes of unusually high oxidation states, we have obtained in the present study a formal mononuclear Ni(IV)-nitrate complex (2) upon 1-e- oxidation of its Ni(III) derivatives (1-OH and 1-NO3). Characterization of these Ni complexes by combined spectroscopic and computational approaches enables deep understanding of their geometric and electronic structures, bonding interactions, and spectroscopic properties, showing that all of them are square planar complexes and exhibit strong π-covalency with the amido N-donors of the N3 ligand. Furthermore, results obtained from X-ray absorption spectroscopy and density functional theory calculations provide strong support for the assignment of the Ni(IV) oxidation state of complex 2, albeit with strong ligand-to-metal charge donation. Notably, 2 is able to oxidize hydrocarbons with C-H bond strength in the range of 76-92 kcal/mol, representing a rare example of high-valent late transition metal complexes capable of activating strong sp3 C-H bonds.

Physico-chemical characterizations and biological evaluation of a new semiconducting metal–organic compound based on pyrimidine frameworks

A new complex with the formula (C5H8N3)2[NiCl2(C5H7N3)2(H2O)2].2Cl (1) was synthesized in good yields and fully characterized. X-ray diffraction analysis, suggests that 1 is mononuclear nickel(II) complex and exhibits distorted octahedral geometry. Each octahedron is building from nickel(II) ion presenting the center and two nitrogen atoms from two organic ligands, two chloride ions, and two oxygen coming from aqua molecules, which occupy the six vertices. The supramolecular architecture can be described essentially as an alternating distribution of nickel octahedra and pyrimidine rings, some are oriented along [011] direction and the others follow the orientation [01 1¯ ]. This network is linked by three types of hydrogen bonds, N–H…Cl, N–H…N, and OW–H…Cl. The optical properties of the crystal were studied using UV–visible spectroscopy and the gap energy value was estimated to be 3.34 eV. The docking simulation showed acceptable binding affinities (between –4.5 and –6.3 kcal/mol), which together with the druglikeness explain the possible biological activities of the compound and its promising effects. Further in vitro and/or in vivo analyses might confirm the in silico simulation results. The analysis of the magnetic properties and ab initio calculations suggest that 1 can be described as quasi-one-dimensional anisotropic S = 1 ferromagnet with zero-field splitting parameters D/kB = 6.3 K and in-chain exchange coupling J/kB = 4.3 K.