An octahedral nickel(II) complex of a hexadentate N<Subscript>2</Subscript>O<Subscript>2</Subscript>S<Subscript>2</Subscript> thioether ligand: synthesis,characterization, X-ray and electronic structure

A hexadentate dibasic thioether N₂O₂S₂ donor ligand (H ₂ L) and its octahedral nickel(II) complex, [Ni(L)] have been synthesized and characterized by physicochemical and spectroscopic techniques. The structures of both H ₂ L and its nickel complex were confirmed by single-crystal X-ray diffraction studies. The cyclic voltammogram of the complex shows a quasi-reversible Ni(II)/Ni(III) oxidation couple (E _1/2 = 0.88 V) along with a ligand-based reduction (E _1/2 = ?0.83 V). The electronic structures and electrochemical properties have been interpreted with the help of DFT calculations. The electronic transitions as calculated by TDDFT/CPCM method are used to assign the UV–Vis absorption bands.     

Effect of the Structure of Pyridine Ligands and the Substituent in the Carboxylate Anion on the Geometry of Transition Metal Complexes [M<Subscript>2</Subscript>(O<Subscript>2</Subscript>CR)<Subscript>4</Subscript>L<Subscript>2</Subscript>]

A series of binuclear tetracarboxylate-linked Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) complexes with 1,2-substituted pyridine, viz., 2,3-cyclododecenopyridine (L), were prepared. Study of the crystal structures of isolated compounds (CIF file CCDC nos. 1575855–1575859) revealed a distortion of the {Ni₂(O₂CR)₄L₂} binuclear moiety, manifested as a change in the NiNiN angle (151.67°), in the bridging function of two out of the four carboxylate groups (from μ_2- to (κ²,μ_2-)), and in the coordination environment of the metal ion (NiO₅N). The results were analyzed in comparison with known data. The magnetic properties of copper(II) and nickel(II) complexes were studied. The copper(II) complex is diamagnetic as a result of strong exchange interactions between the unpaired electrons; in the nickel(II) complex antiferromagnetic exchange interactions were detected (J_Ni–Ni =–25 cm^–1).     

Synthesis and physicochemical study of Ni<Superscript>II</Superscript> complexes with tetradentate acyclic and macrocyclic N<Subscript>2</Subscript>S<Subscript>2</Subscript> ligands as thiosalen analogs

N,N’-Polymethylenebis(thiosalicylidene)iminate and macrocyclic dithiadiazadibenzocycloalkadiene complexes of nickel(II) were synthesized and their electrochemical and spectroscopic properties were studied. Dithiadiazadibenzocycloalkadiene complexes containing two DMSO molecules coordinated to Ni²⁺ and two outer-sphere ClO₄ ⁻ anions were synthesized by the reaction of the corresponding macrocyclic ligands with Ni(ClO₄)₂·6H₂O. The structure of 3,6-dithia-10,14-diazadibenzo[a,g]cyclopentadeca-9,14-dienylnickel(II)[bis(dimethyl sulfoxide) bis-perchlorate] was established by X-ray diffraction. The UV-Vis spectroscopic data are consistent with octahedral structures of diiminobis(sulfide) complexes, a square-planar structure of the thiosalen complex, and distorted tetrahedral structures of other diiminodithiolate complexes. The reaction of S-tert-butylthiosalicylaldehyde with hydrazine hydrate afforded di(ortho-tert-butylthiobenzal)azine. The reaction of the latter with anhydrous NiCl₂ produced a colored complex with the simplest molecular formula Ni(C₁₆H₁₂N₂S₂) in 15% yield. Semiempirical PM3(tm) calculations and the results of UV-Vis, ESR, and ¹H NMR spectroscopy demonstrate that this complex has most probably a dimeric structure, in which two Ni centers adopt a nearly square-planar configuration. The complexes are clearly divided into two types according to their electrochemical behavior in DMF solutions. The type 1 is characterized by reversibility of the first reduction steps. The type 2 is characterized by irreversible two-electron reduction as the first step accompanied by deposition of Ni metal on the electrode surface. Rapid electrochemically initiated alkylation occurs in the presence of various alkylating agents (BuⁿI, BuⁿBr, (DmgH)₂CoCH₃) in a solution of complex 1 in DMF.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 169–183, January, 2005.     

Molecular structure of NiO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript> from gas-phase electron diffraction and quantum chemical data

Gas-phase electron diffractometry was used to study the molecular structure of N,N′-ethylenebis(salicylaldiminato)nickel(II), NiO₂N₂C₁₆H₁₄, [hereinafter Ni(salen)] at 583(5) K. The molecule has C ₂ symmetry with a practically planar structure of the NiN₂O₂ coordination unit and with internuclear distances r _α (Ni-O) = 1.882(21) Å and r _α (Ni-N) = 1.889(22) Å. The results of B3LYP/CEP-31G molecular structure calculations are in good agreement with experimental data, whereas the RHF/CEP-31G method significantly overestimates the Ni-N internuclear distance and gives worse results for other structural parameters. According to 3LYP/CEP-31G calculations, the ¹ A low-spin state is 28 kJ/mole lower in energy than the ³ B high-spin state.     

Hydrothermal synthesis and crystal structure of [Ni(Bptc)<Subscript>2</Subscript>(Bimb)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>]

In the compound [Ni(Bptc)₂(Bimb)₂(H₂O)₂] (I), where H₄Bptc is 3,3′,4,4′-biphenyltetracarboxylic acid; Bimb is 4,4′-bis(1-imidazolyl)biphenyl), Ni(II) has a distorted octahedral coordination geometry, which was bonded with two N atoms from two Bimb ligands, two O atoms from two H₂Bptc²⁻ ligands and two water O atoms. The crystal structure of compound I is stabilized by the π-π-stacking and hydrogen bonds interaction.     

Activity and stability of Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in carbon dioxide conversion of methane as influenced by alkali metal oxide additives (K<Subscript>2</Subscript>O,Na<Subscript>2</Subscript>O,Li<Subscript>2</Subscript>O)

Properties of Ni/Al₂O₃ composites supported by synthetic cordierite ceramic block matrices of honeycomb structure in carbon dioxide conversion of methane in the presence of alkali metal oxides (K₂O, Na₂O, Li₂O) were studied in comparison with those of GIAP-18 granulated catalyst.     

Synthesis and structural characterization of a novel trinickel cluster: {[Ni(H<Subscript>2</Subscript>L)(EtOH)]<Subscript>2</Subscript>(OAc)<Subscript>2</Subscript>Ni} · 2EtOH

A novel trinuclear Ni^II cluster, {[Ni(H₂L)(EtOH)]₂(OAc)₂Ni} · 2EtOH [H₄L:5,5′-Dihydroxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol], has been synthesized and structurally characterized. The X-ray crystal structure of the cluster reveals that two acetates coordinate to three nickel ions through Ni–O–C–O–Ni bridges and four μ-phenoxo oxygen atoms from two [Ni(H₂L)] units also coordinate to nickel ions. Around three nickel atoms are all octahedral geometries.     

Novel large heteropolymetalate complexes formed from Ni(II) and cryptate [As<Subscript>4</Subscript>W<Subscript>40</Subscript>O<Subscript>140</Subscript><Superscript>28-</Superscript>

The heteropolytungstate (NH4)₂₀[Na2(H₂O)₂Ni(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀] · 61H₂O is obtained by the reaction of Na₂₇[NaAs₄W₄₀O₁₄₀] · 60H₂O with NiCl₂ · 6H₂O and NH₄Cl in pH≈4.0. The structure and chemical composition are determined by X-ray diffraction analysis and element analysis. The crystal data and main structure refinement are: a = 1.33135(18) nm, b = 1.9722(3) nm, c = 3.6430(5) nm, α = 78.010(2)°, β = 82.145(2)δ, γ = 74.385(2)°, V = 8.978(2) nm³, triclinic crystal system, space group: P1, Z = 2, R1 = 0.0512, and wR2 = 0.0684(I >2σ). The four S2 sites of the big cyclic ligand [As₄W₄₀O₁₄₀]^28- are occupied by two Na⁺ and two Ni²⁺ respectively, and each site supplies four O_d coordinating to metal ion. The coordination number of Ni²⁺ is six, and that of two Na⁺ is five and six respectively. The third Ni²⁺ locates outside the cyclic [As₄W₄₀O₁₄₀]^28- and connects with one O_d, and its coordination number is six.     

Supramolecular architecture of the [M(1-MeIm)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>]<Superscript>2+</Superscript> (M = Ni,Co) complexes with the terephthalate anion

The [M(1-MeIm)₂(H₂O)₄](Tpht) · 4H₂O complexes (where M = Ni, Co; 1-MeIm is 1-methylimidazole; H₂Tpht is terephthalic acid) are synthesized and characterized by X-ray diffraction analysis. The ionic structure is built of the [M(1-MeIm)₂(H₂O)₄]²⁺ cations and (Tpht)^2? anions. The metal ions have a distorted octahedral coordination. The cations and anions are united by hydrogen bonding system.     

Ligand Exchange in Pd(II)-NaCl-H<Subscript>2</Subscript>O and Pd(II)-HCl-H<Subscript>2</Subscript>O Systems: Quantum-Chemical Consideration

The behavior of potassium tetrachloropalladate(II) in media simulating biological liquids is studied. The rate of aquation in aqueous NaCl solutions is shown to be higher than the rate at which the Cl^? ligand enters the inner coordination sphere of the Pd atom. In HCl solutions, the formation of the Pd chloro complexes predominates due to protonation of water molecules in the composition of aqua complexes. The reactions of replacement of the ligands (H₂O molecules and H₃O⁺ ion) in the planar Pd(II) complexes by the chloride ion are studied by the ZINDO/1 method. All the complexes containing H₂O and H₃O⁺ ligands, except for [Pd(H₂O)₄]²⁺, contain intramolecular hydrogen bonds. The ZINDO/1 and RHF/STO-6G(d) calculations revealed “nonclassic” symmetrical O? H?O hydrogen bond in the [[Pd(H₂O)₃(H₃O)]³⁺ and trans-[Pd(H₂O)₂(H₃O)Cl]²⁺ complexes. The replacement of the H₃O⁺ ion by the Cl^? ion at the first three steps is thermodynamically more advantageous than the displacement of water molecules from the metal coordination sphere. The logarithms of stepwise stability constants of Pd(II) chloro complexes are found to correlate linearly with the enthalpies (ZINDO/1, PM3) of reactions of H₂O replacement by Cl^?.     

Synthesis,characterization, fluorescence and redox features of new <Emphasis Type="Italic">vic</Emphasis>-dioxime ligand bearing pyrene and its metal complexes

A new vic-dioxime ligand, N,N′-bis(aminopyreneglyoxime) (LH₂), and its copper(II), nickel(II) and cobalt(II) metal complexes were synthesized and characterized by elemental analyses, IR, UVVIS and ¹H and ¹³C NMR spectra (for the ligand). Mononuclear complexes were synthesized by a reaction of ligand (LH₂) and salts of Co(II), Ni(II), and Cu(II) in ethanol. The complexes have the metal-ligand ratio of 1: 2 and metals are coordinated by N,N′ atoms of vicinal dioximes. The ligand acts in a polydentate fashion bending through nitrogen atoms in the presence of a base, as do most vic-dioximes. Detection of a H-bonding in the Co(II), Ni(II), and Cu(II) complexes by IR revealed the square-planar MN₄ coordination of mononuclear complexes. Fluorescent properties of the ligand and its complexes arise from pyrene units conjugated with a vic-dioxime moiety. Fluorescence emission spectra of the ligand showed a drastic decrease in its fluorescence intensity upon metal binding. The electrochemical properties of the complexes were studied by the cyclic voltammetry technique. The nickel complex displayed an irreversible oxidation process while the copper complex exhibited a quasi-reversible oxidation and reduction processes based on the copper Cu(II)/Cu(III) and Cu(II)/Cu(I) couples, respectively.     

Synthesis of Ni/SiO<Subscript>2</Subscript> nanoparticles for catalytic benzene hydrogenation

Nickel nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium. The obtained solids were characterized by X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Electron Diffraction (ED), hydrogen chemisorption, and Temperature Programmed Desorption of hydrogen (H₂-TPD). The catalytic properties were evaluated for benzene hydrogenation in the temperature range 75–230 °C. XRD patterns reveal presence of the metallic nickel particles with fcc structure. Metal dispersion and hydrogen storage increase with decreasing metal particle size. The H₂-TPD profiles exhibit two domains, one due to desorption of hydrogen from Ni metal and another due to spillover from metal to the support. The catalytic activity strongly depends on the metal loading. It increases with decreasing metal loading. This is attributed to metal surface area, which also increases with decreasing metal loading. Kinetic studies of benzene hydrogenation on the Ni catalysts showed that the benzene partial order is around −2. This significant negative value is ascribed to a strong adsorption of benzene on the catalyst surface.     

Ni(II) and Cu(II) complexes of new unsymmetrical N2O2 Schiff bases derived from 3-(2-aminobenzylimino)-1-phenylbutan-1-ol: synthesis,structure, antibacterial properties,and electrochemistry

Two new N₂O₂ unsymmetrical Schiff bases, H₂L¹ = 3-[({o-[(E)-(o-hydroxyphenyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol and H₂L² = 3-[({o-[(E)-(2-hydroxy-1-naphthyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol, and their copper(II) and nickel(II) complexes, [CuL¹] (1), [CuL²] (2), [NiL¹] (3), and [NiL²] (4), have been synthesized and characterized by elemental analyses and spectroscopic methods. The crystal structures of these complexes have been determined by X-ray diffraction. The coordination geometry around Cu(II) and Ni(II) centers is described as distorted square planar in all complexes with the CuN₂O₂ coordination more distorted than the Ni ones. The electrochemical studies of these complexes indicate a good correlation between the structural distortion and the redox potentials of the metal centers. The ligand and metal complexes were also screened for their in vitro antibacterial activity.     

Variation in coordinative property of two different N<Subscript>2</Subscript>O<Subscript>2</Subscript> donor Schiff base ligands with nickel(II) and cobalt(III) ions: characterisation and single crystal structure elucidation

A nickel(II) and a cobalt(III) complex of two different potentially tetradentate Schiff bases with different binding modes have been synthesised. The nickel(II) complex [NiL¹] · CH₃OH (1) was formed, on reacting the metal salt with a perfectly symmetrical N₂O₂ tetradentate Schiff base ligand H ₂ L ¹ , which is the 1:2 condensation product of 1,3-diamino propane and 2-hydroxyacetophenone. The cobalt(III) complex [Co(HL²)₃] · (ClO₄)₃ · H₂O (2) was synthesised using an asymmetric N₂O₂ tetradentate Schiff base ligand HL ² on condensing N,N-dimethyl-1,3-diamino propane with o-vanillin in 1:1 mmol ratio. Although both Schiff bases are N₂O₂ functionalised, they showed variation in their coordinative property with nickel(II) and cobalt(III) ions. Both the complexes were characterised by IR spectroscopy and cyclic voltammetry and their single crystal structures clearly indicate that 1 is a mononuclear species whereas 2 is a hydrogen-bonded dimer.     

A review on nanomaterial-based electrochemical sensors for H<Subscript>2</Subscript>O<Subscript>2</Subscript>, H<Subscript>2</Subscript>S and NO inside cells or released by cells

The incorporation of nanomaterials into electrochemical sensors is an attractive approach towards the improvement of the sensitivity of amperometry and also can provide improved sensor selectivity and stability. This review (with 137 references) details the current state of the art and new trends in nanomaterial-based electrochemical sensing of hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S) and nitric oxide (NO) in cells or released by cells. The article starts with a discussion of the significance of the three analytes, and this is followed by three sections that summarize the electrochemical detection schemes for H₂O₂, H₂S and NO. Each section first summarizes the respective physiological roles, and then reviews electrochemical sensors based on the use of carbon nanomaterials, noble metal nanomaterials, metal oxide nanomaterials, and layered doubled hydroxides. The materials are compiled in three tables along with figures of merit for the various sensors.

Open image in new window

Graphical abstract Nanomaterial-based electrochemical sensors for Reactive oxygen species (H₂O₂), Reactive nitrogen species (NO) and Reactive hydrogen sulfide species (H₂S) inside cells or released by cells.

     

Trimetallic NiMoW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalyst based on H<Subscript>4</Subscript>SiMo<Subscript>3</Subscript>W<Subscript>9</Subscript>O<Subscript>40</Subscript> mixed heteropoly acid

Trimetallic NiMoW/Al₂O₃ catalyst was prepared using mixed H₄SiMo₃W₉O₄₀ heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts based on H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀, respectively, were synthesized as reference samples. The use of mixed H₄SiMo₃W₉O₄₀ heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al₂O₃ catalyst. The synergistic enhancement of the activity of the NiMo₃W₉/Al₂O₃ catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.     

Peculiarities of polythermic decomposition of iron,cobalt and nickel oxalates within pores of photonic crystals based on SiO<Subscript>2</Subscript> in atmosphere with oxygen lack

Iron(II), cobalt(II) and nickel(II) oxalates were synthesized as nanofractals inside the voids of the photonic crystals based on SiO₂. Guest substances undergone polythermic decomposition within the pores of the photonic crystals in helium atmosphere containing of oxygen traces (∼1 Pa) under static conditions. Pyrolysis of Fe(COO)₂·2H₂O, Co(COO)₂·2H₂O and Ni(COO)₂·2H₂O studied by TG and DSC techniques results in the formation of the metal oxides. The nanoparticles of Fe₂O₃, CoO (Co₃O₄) and NiO populated the interspheric voids of the photonic crystals exhibited no ferromagnetic effects indicating that no metallic inclusions were formed in helium in the presence of O₂ traces. The exothermic effect was observed by the thermal decomposition of the cobalt(II) oxalate only under oxygen lack.     

Nano-Architecture of Facetted NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/(Ni,Fe)O Particles Produced by Induction Plasma

Facetted nickel ferrite (NiFe₂O₄) and bunsenite [(Ni,Fe)O] nanocrystals were grown from the decomposition of iron and nickel nitrate precursors using an inductively coupled plasma reactor. The full range of the two-phase region of the Fe₂O₃–NiO pseudo-equilibrium phase diagram was investigated by producing nanopowders with bulk Ni/(Ni + Fe) ratios of 0.33, 0.4, 0.5, 0.75 and 1.0. A Ni-poor [Ni/(Ni + Fe) ≤ 0.5] precursor solution produced truncated octahedron nanocrystals, whereas nanocubes were obtained at higher ratios [Ni/(Ni + Fe) ≈ 1]. In both cases, it is shown that the nanocrystals adopt a morphology close to the Wulff shape of the crystalline system (spinel and NaCl, respectively). As the bulk Ni/(Ni + Fe) ratio increases from 0.33 (the stoechiometric composition of nickel ferrite), bunsenite is epitaxially segregated on the {110} and {111} facets of nickel ferrite, while leaving the NiFe₂O₄ {100} facets exposed. A precursor solution at a Ni/(Ni + Fe) ratio of 0.75 gave an (Ni,Fe)O-rich nanopowder with a random and irregular interconnected morphology. The structure of these nanocrystals can be understood in terms of their thermal history in the plasma reactor. These results highlights the possibility of producing organized multi-phased nanomaterials of binary systems having two phases stable at high temperatures, using a method known to be easily scalable.     

Two New {P<Subscript>8</Subscript>W<Subscript>49</Subscript>} Wheel-shaped Tungstophosphates Decorated by Co(II), Ni(II) Ions

Two new wheel-shaped tungstophosphates based on 3d-transition metals (Co(II), Ni(II)) ions decorated [P₈W₄₉O₁₈₇]⁴⁰⁻ anion (TM-{P₈W₄₉}), K₄Na₂₂{[Co(H₂O)₂Cl][Co(H₂O)₃]₂[Co(H₂O)₅]_1.5 [Co(H₂O)₃H₄P₈W₄₉O₁₈₇(H₂O)]}·2NaCl·41·5H₂O 1 and Na₃₀{[Ni(H₂O)₃]₂[{Ni(H₂O)₃}_1.5H₃P₈W₄₉O₁₈₇ (H₂O)]}·41.5H₂O 2 have been synthesized by routine synthetic reaction of hexavacant Dawson polyoxonanion [P₂W₁₂O₄₈]¹⁴⁻ with divalent 3d transition-metal ions in aqueous solution. The two compounds are characterized by elemental analysis, IR spectroscopy, TG analysis, electrochemical analysis, and single-crystal X-ray diffraction. Both compounds contain a 2D layer-like structure constructed from 1D chains of wheel-type [P₈W₄₉O₁₈₇]⁴⁰⁻ anions bridged via CoO₆ or NiO₆ units. Cyclic voltammograms and ³¹P NMR analysis suggest that the polyanion [P₈W₄₉O₁₈₇]⁴⁰⁻ of both compounds are stable in aqueous solution (pH = 4).     

Electrochemical Behavior of Cobalt-Dimethylglyoxime Complex Co(DMG)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript> in the Carbon Dioxide Reduction Process

The electrochemical behavior of a complex of cobalt with dimethylglyoxime Co(DMG)₂(H₂O)₂ is studied by cyclic voltametry. Peaks corresponding to redox transitions Co(III)/Co(II) and Co(II)/Co(I) are observed in the potential region 0.4 to ?1.8 V (Ag/AgCl). The product of reduction of the initial complex interacts with carbon dioxide to form a stable compound, probably an intermediate product of electrocatalytic reduction of CO₂ to CO in the presence of N₄-macrocyclic complexes of cobalt.