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The experiment aimed to study the antibacterial activity and mechanism of 4-substituted terpyridine cobalt and nickel complexes. The experiment used the two-fold dilution method to determine the minimum inhibitory concentration (MIC) of 10 different 4-substituted terpyridine cobalt and nickel metal complexes against six common pathogenic bacteria (Salmonella enterica, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli K99, Streptococcus agalactiae, and Vibrio parahaemolyticus), and analyzed their antibacterial activity. The results showed that the complexes had good inhibitory effects on Staphylococcus aureus, with generally low MIC values, among which the MIC of LB3 NiCl2 against Staphylococcus aureus was as low as 5 mg/L. The growth curve and death curve of Staphylococcus aureus showed that LB3 NiCl2 inhibited bacterial growth to varying degrees and had concentration dependence. The results of fluorescence microscopy observation showed that the permeability of bacterial cell membranes increased after treatment with metal complexes. The study indicates that 4-substituted terpyridine cobalt and nickel complexes have good antibacterial activity against Staphylococcus aureus. [ABSTRACT FROM AUTHOR]

Invasive fungal diseases affect more than two million people worldwide. The increasing incidence of invasive fungal infections is the result of many factors, including an increase in the resistance to current drugs. As such, there is an urgent need to obtain new drugs that are efficient, selective, and able to overcome existing resistance mechanisms. Candida yeasts are responsible for more than 70% of all nosocomial invasive fungal diseases. In this work, we describe the synthesis of nickel (II)(NHC) complexes based on xanthines, by direct metalation of xanthinium salts with nickelocene NiCp2to yield [NiCpI(NHC)] complexes. For methyl caffeine, a biscarbene complex [NiCp(NHC)2]+is also formed, resulting from carbene dissociation from the corresponding monocarbene. [NiCpI(NHC)] complexes are active as antifungals for Candida yeasts and show toxicity for human cells (HeLa) that is dependent on the substitution of N7 of the xanthine moiety. The biscarbene complex 5[NiCp(NHC)2]+is highly selective for Candida glabrata and shows very low toxicity for human cells, being a promising candidate for selective treatment of C. glabrata infections. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of two nickel complexes 7 and 8 based on 1,2,4-triamino-5-nitrobenzene 6. The formation of these compounds is observed from the same precursor, their stoichiometry depending on the nature of the solvent used for the crystallization. The key role of the nitro group in 6 is discussed, demonstrating its major impact on the stability and reactivity of the ligand. Each nickel complex could be characterized by single crystal X-ray analysis, highlighting the importance of the intramolecular H-bonding interactions on the stability of the complexes incorporating a monodentate aromatic amine-type ligand.

The eleven new copper(II) and nickel(II) coordination compounds [Cu(L)Br]2 (1), [Cu(L)Cl] (2), [Cu(L)NO3] (3), [Ni(L)Cl] (4), [Ni(HL)2](NO3)2 (5), and [Cu(A)(L)]NO3, where A is 1,10-phenanthroline (6), 2,2′-bipyridine (7), 3,4-dimethylpyridine (8), 3-methylpyridine (9), pyridine (10) and imidazole (11) were synthesized with 3-(morpholin-4-yl)propane-2,3-dione 4-allylthiosemicarbazone (HL). The new thiosemicarbazone was characterized by NMR and FTIR spectroscopy. All the coordination compounds were characterized by elemental analysis and FTIR spectroscopy. Also, the crystal structures of HL and complexes 1, 6, 7, and 11 were determined using single-crystal X-ray diffraction analysis. Complex 1 has a dimeric molecular structure with two bromide bridging ligands, while 6, 7, and 11 are ionic compounds and comprise monomeric complex cations. The studied complexes manifest antibacterial and antifungal activities and also have an antiradical activity that, in many cases, surpasses the activity of trolox, which is used as a standard antioxidant in medicine. Copper complexes 1–3 have very weak antiradical properties (IC50 > 100 µM), but nickel complexes 4–5 are strong antiradicals with IC50 values lower than that of trolox. The mixed ligand copper complexes with additional ligand of N-heteroaromatic base are superior to complexes without these additional ligands. They are 1.4–5 times more active than trolox. [ABSTRACT FROM AUTHOR]

This study aims to advance the field of green chemistry and catalysis by exploring alternatives to conventional non-renewable energy sources. Emphasis is placed on hydrogen as a potential fuel, with a focus on the catalytic properties of Ni(II) complexes when coordinated with o-phenylenediamine and diimine ligands. We report the synthesis and comprehensive characterization, with various physical and spectroscopic techniques, of three heteroleptic Ni(II) complexes: [Ni(1,10-phenanthroline)(o-phenylene diamine)] (1), [Ni(2,2-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (2), and [Ni(5,5-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (3). The catalytic activity of these complexes for hydrogen evolution was assessed through photochemical studies utilizing visible light irradiation. Two distinct photosensitizers, fluorescein and quantum dots, were examined under diverse conditions. Additionally, their electrocatalytic behavior was investigated to elucidate the hydrogen evolution reaction (HER) mechanism, revealing a combined proton-coupled electron transfer (PCET)/electron-coupled proton transfer (ECPT) mechanism attributed to the chemical nature of the diamine ligand. The influence of ligand substituent position, ligand chemical nature, and photosensitizer type on catalytic performance was systematically studied. Among the complexes investigated, complex 2 demonstrated superior catalytic performance, achieving a turnover number (TON) of 3357 in photochemical experiments using fluorescein as a photosensitizer. Conversely, complex 1 exhibited the highest TON of 30,066 for HER when quantum dots were employed as the photosensitizer. [ABSTRACT FROM AUTHOR]

[Display omitted] A user-friendly and highly efficient mechanochemical synthesis of Ni/NHC complexes of the general formula (NHC)Ni(Cp)Cl (NHC is an N-heterocyclic carbene ligand; Cp is the cyclopentadienyl anion) under aerobic conditions is reported. The reaction between nickelocene and azolium salts (NHC proligands) proceeds with good to excellent yields of (NHC)Ni(Cp)Cl in the presence of a K 2 CO 3 additive, which reduces the clumping of the reaction mixture. The developed process can be scaled up on a planetary ball mill. [ABSTRACT FROM AUTHOR]

The extensive industrial use of organic dyes causes large amounts of these substances to arrive at water sources, so nowadays, organic compound removal from fresh water is a major concern. The use of photocatalysts is an interesting approach to solving this problem, with coordination compounds playing an outstanding role. We report the selective synthesis and characterization of three new dissymmetric bis(thiosemicarbazone) ligands and their nickel(II) and zinc(II) complexes, which have been fully characterized by several techniques. The photocatalytic activity of the six complexes for methyl orange degradation was also evaluated. All the complexes can degrade this organic dye, although the photoefficiency of the nickel compounds is, in general, higher than for the zinc ones, as the degradation is faster and they do not reach a plateau. Density functional theory calculations show a clear dependence of the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap, as well as with the relative energies of these orbitals. On the other hand, the need for green fuels that do not produce the greenhouse effect is one of the major goals of modern life, and molecular hydrogen is one of the most promising ones. Considering the proven potential of bis(thiosemicarbazone) complexes to electrocatalyze H2 evolution recently reported in the literature, we also made some preliminary tests to investigate the potential of the nickel complexes to act as photocatalysts for water splitting. The results indicate that two of the complexes produce H2 in the conditions tested, so they could be used in the development of efficient photocatalytic systems for hydrogen evolution. [ABSTRACT FROM AUTHOR]

Processing CO2 into value–added chemicals and fuels stands as one of the most crucial tasks in addressing the global challenge of the greenhouse effect. In this study, we focused on the complex (dpp–bian)NiBr2 (where dpp–bian is di‐isopropylphenyl bis‐iminoacenaphthene) as a precatalyst for the electrochemical reduction of CO2 into CH4 as the sole product. Cyclic voltammetry results indicate that the realization of a catalytically effective pattern requires the three–electron reduction of (dpp–bian)NiBr2. The chemically reduced complexes [K(THF)6]+[(dpp–bian)Ni(COD)]− and [K(THF)6]+[(dpp–bian)2Ni]− were synthesized and structurally characterized. Analyzing the data from the electron paramagnetic resonance study of the complexes in solutions, along with quantum–chemical calculations, reveals that the spin density is predominantly localized at their metal centers. The superposition of trajectory maps of the electron density gradient vector field ∇ρr ${\nabla \rho \left({\bf r}\right)}$ and the electrostatic force density field Fesr ${{{\bf F}}_{{\rm e}{\rm s}}\left({\bf r}\right)}$ per electron, as well as the atomic charges, discloses that, within the first coordination sphere, the interatomic charge transfer occurs from the metal atom to the ligand atoms and that the complex anions can thus be formally described by the general formulae (dpp–bian)2−Ni+(COD) and (dpp–bian)2−Ni+. It was also shown that the reduced nickel complexes can be oxidized by formic acid; resulting from this reaction, the two–electron and two–proton addition product dpp–bian–2H is formed. [ABSTRACT FROM AUTHOR]

The anti (a) to syn (s) isomerization pathway of the deprotonated form of the dimer with two nickel(II) 15-membered octaazamacrocyclic units connected via a carbon–carbon (C–C) σ bond was investigated. For the initial anti (a) structure, a deprotonation of one of the bridging (sp3 hybridized) carbon atoms is suggested to allow for an a to s geometry twist. A 360° scan around the bridging C–C dihedral angle was performed first to find an intermediate geometry. Subsequently, the isomerization pathway was explored via individual steps using a series of mode redundant geometry optimizations (internal coordinates potential energy surface scans) and geometry relaxations leading to the s structure. The prominent geometries (intermediates) of the isomerization pathway are chosen and compared to the a and s structures, and geometry relaxations of the protonated forms of selected intermediates are considered. [ABSTRACT FROM AUTHOR]

A 2D material few-layer black phosphorus (FLBP) has promising applications in various fields of chemistry and physics due to its unique electronic and optical properties. Chemical functionalization of the FLBP surface is an effective strategy for improving the oxidative stability of the material, tuning its intrinsic properties or endowing it with new properties. The present work proposes an approach to the immobilization of the [NiBr2(phen)] complex (phen = 1, 10-phenanthroline) on the FLBP surface via covalent functionalization of FLBP with 1,10-phenanthroline and subsequent complexation with NiBr2. The obtained FLBP-based materials functionalized by the [NiBr2(phen)] complex were characterized by a set of physicochemical methods such as transmission electron microscopy, atomic force microscopy, solid-state NMR, energy-dispersive spectroscopy, Raman spectroscopy, and IR spectroscopy. [ABSTRACT FROM AUTHOR]

Direct and stereodivergent Michael additions of N‐acyl 1,3‐thiazinane‐2‐thiones to α,β‐unsaturated aldehydes catalyzed by chiral nickel(II) complexes are reported. The reactions proceed with a remarkable regio‐, diastereo‐, and enantioselectivity, so access to any of the four potential Michael stereoisomers is granted through the appropriate choice of the chiral ligand of the nickel(II) complex. Simple removal of the heterocyclic scaffold furnishes a wide array of either syn or anti enantiomerically pure derivatives, which can be exploited for the asymmetric synthesis of biologically active compounds, as demonstrated in a new approach to tapentadol. In turn, a mechanism, based on theoretical calculations, is proposed to account for the stereochemical outcome of these transformations. [ABSTRACT FROM AUTHOR]

Herein, we report for the first time the use of the nitrogen‐based bidentate molecule [2.2]pyridinophane (N2) as a ligand for metal complexes. Additionally, its improved synthesis allows for electronic modification of the pyridine rings to access the new para‐dimethylamino‐[2.2]pyridinophane ligand (p‐NMe2N2). These ligands bind nickel in an analogous fashion to other pyridinophane ligands, completing the series of tetra‐, tri‐, and bidentate pyridinophane‐nickel complexes. The new compounds exhibit geometrically enforced C−H anagostic interactions between the ethylene bridge protons and the nickel center that are not present in other pyridinophane systems. These ethylene bridge groups also act as an unusual form of steric encumbrance, enforcing square planar geometries in ligand fields that would otherwise adopt tetrahedral structures. In addition, these anagostic interactions inhibit the catalytic performance in Csp3–Csp3 Kumada cross coupling reactions relative to other common bidentate N‐ligand platforms, possibly by preventing the formation of the 5‐coordinate oxidative addition intermediates. [ABSTRACT FROM AUTHOR]

New binary and mixed‐ligand nickel (II) chelates of a hyrdazone ligand (HYQX) carrying alloxan and quinoline moieties were synthesized. Spectroscopic and analytical techniques were effectively used for identifying the composition and structure of the prepared nickel (II) HYQX chelates. The neutral nature of Ni‐HYQX complexes was demonstrated by molar conductivity studies, and magnetic moment values revealed octahedral geometry. The results demonstrated that HYQX behaves as a monoanionic di‐/tridentate chelating agent in all complexes, except nitrato C2 and acetato C4 complexes, which are bi‐ and tri‐nuclear complexes, respectively, with a unique mode of coordination. The thermal decomposition patterns of Ni‐HYQX complexes were investigated in relation to structure, and thermodynamic parameters were successfully calculated. The molecular structural features of HYQX and its Ni (II) chelates were investigated based on density functional theory (DFT) level at B3LYP/6‐311G(d,p) and LanL2dz level. Ni‐HYQX complexes were found to have anticancer action against Ehrlich Ascites Carcinoma. A molecular docking investigation was conducted to determine in what way the title compounds connect to the CDK‐5 inhibitor‐crystal structure of the inhibitor EFP with CDK‐2 (PDB ID: 3IG7) in order to verify their biological activity. [ABSTRACT FROM AUTHOR]

It has been shown in tests that N-heteroaryl-substituted α-diphenylphosphinoglycines, namely, N-(pyrazin-2-yl) α-diphenylphosphinoglycine, N-(pyridin-2-yl) α-diphenylphosphinoglycine, and N‑(pyrimidin-2-yl) α-diphenylphosphinoglycine, which are synthesized by the three-component condensation of diphenylphosphine, the respective primary amine, and glyoxylic acid monohydrate, being combined with Ni(COD)2, where COD is cyclooctadiene-1,5, are capable of generating active forms of catalysts for the selective homogeneous dimerization and trimerization of ethylene to form butene-1 and hexene-1 as the main products. The studied organonichel catalyst systems provide a yield of short-chain (C4–C6) olefins at a level of 90% with a linear α-olefin selectivity of 97%. Studies of the effect of temperature on the homogeneous oligomerization of ethylene using the synthesized compounds have revealed that the process run at an optimum temperature of 80–105°C and an optimum ethylene pressure of 20–35 atm provides the highest butene-1 and hexene-1 selectivity. Under these conditions, the butene selectivity is recorded at a level of 71.4–72.6% (butene-1 selectivity of 69.3–71.1%), while the hexene selectivity is 20.6–21.2% (hexene-1 selectivity of 19.2–19.5%). The optimum duration of the oligomerization process at a temperature of 105°C is 1.5 h. The butene-1 and hexene-1 formation rate is 168.1 and 47.3 golig h–1, respectively. [ABSTRACT FROM AUTHOR]

Solar hydrogen production at a high efficiency holds the significant importance in the age of energy crisis, while the micro‐environment manipulation of active sites on photocatalysts plays a profound role in enhancing the catalytic performance. In this work, a series of well‐defined single‐site Ni‐grafted TiO2 photocatalysts with unique and specific coordination environments, 2,2′‐bipyridine‐Ni−O−TiO2 (T−Ni Bpy) and 2‐Phenylpyridine‐Ni−O−TiO2 (T−Ni Phpy), were constructed with the methods of surface organometallic chemistry combined with surface ligand exchange for visible‐light‐induced photocatalytic hydrogen evolution reaction (HER). A prominent rate of 33.82 μmol ⋅ g−1 ⋅ h−1 and a turnover frequency of 0.451 h−1 for Ni are achieved over the optimal catalyst T−Ni Bpy for HER, 260‐fold higher than those of Ni−O−TiO2. Fewer electrons trapped oxygen vacancies and a larger portion of long‐lived photogenerated electrons (>3 ns, ~52.9 %), which were demonstrated by the electron paramagnetic resonance and femtosecond transient IR absorption, correspond to the photocatalytic HER activity over the T−Ni Bpy. The number of long‐lived free electrons injected from the Ni photoabsorber to the conduction band of TiO2 is one of the determining factors for achieving the excellent HER activity. [ABSTRACT FROM AUTHOR]

[Display omitted] A new method has been developed for synthesizing nitron- type 1,4-dyaryl-3-arylamino-1,2,4-triazolium salts through a stepwise reaction of N,N '-diarylcarbodiimides with aryl hydrazines, trimethyl orthoformate and Me3SiCl. These salts have been utilized as NHC-proligands to prepare novel (NHC) 2 NiCl 2 and (NHC)NiCpCl (Cp = cyclopentadienyl anion) complexes. Catalytic trials of these complexes uncovered a highly effective catalyst for the Suzuki–Miyaura cross-coupling of non-activated aryl chlorides. [ABSTRACT FROM AUTHOR]

Herein, we report four new chiral 1,4,7‐triazacyclononane (TACN) derivatives and their corresponding nickel(II) chloride complexes. All TACN ligands are bearing one chiral N‐substituent and two alkyl (methyl or tert‐butyl) N‐substituents, and we have developed a new synthetic method for the dimethyl‐substituted TACN derivative, in order to prevent the rotational isomers that hinder the cyclization reaction. The nickel complexes change their coordination geometry significantly depending on the steric bulk of the N‐alkyl substituents, from a dinuclear tris(μ‐chloro)dinickel complex to mononuclear Ni‐dichloride and Ni‐chloride complexes. These complexes were then employed in the alkyl‐alkyl Kumada cross‐coupling reaction and revealed that the more sterically hindered ligands produced more homocoupled product rather than the cross‐coupled product, while the mononuclear Ni‐dichloride complex exhibited significantly lower catalytic activity. These chiral complexes were also employed in enantioconvergent cross‐coupling reactions as well, to afford significant enantioenrichment. Overall, the least sterically hindered Ni complex yields the best yields in the alkyl‐alkyl Kumada cross‐coupling reaction among the four complexes investigated, as well as the highest enantioselectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] A new complex of nickel acrylate and 4 ' -phenyl-2,2 ' :6 ' ,2 " - terpyridine, analogs of which have been previously used to obtain self-healing metallopolymers, has been prepared. The complex was analyzed by X-ray diffraction, IR and UV absorption spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The values of effective activation energy of solid-phase polymerization and heat of double bond opening for this complex have been calculated. [ABSTRACT FROM AUTHOR]

Five new nickel complexes of the type NiCl2L2 where (L is 4-picolylchloride (4PY), pyridin-4-ylmethyl 4-nitrobenzoate (L1), 4-(pyridine-4-ylmethoxy)aniline (L2), pyridin-4-ylmethyl 4-aminobenzoate (L3) and 4-((4-nitrophenoxy)methyl)pyridine (L4)) were synthesized, characterized, and evaluated for their ability to inhibit bacterial growth. Four of the complexes were synthesized using a green method of co-grinding using a pestle and mortar. All the complexes synthesized by the mechanochemical method were recovered at favorable yields between 70 and 78%, while Ni4PY was recovered at 47.1%. The thermal studies showed the different transformations of the complexes and their thermal stability through Differential Scanning Calorimetry (DSC), while Thermogravimetric analysis (TGA) showed the loss of different components of the complexes cementing their successful synthesis. FTIR data revealed all the significant functional groups originating from the ligands in the new complexes. The characterization results demonstrated the successful synthesis of these complexes. Electronic spectra and magnetic susceptibility studies showed all the complexes to be d8 tetrahedral, except NiL1 which showed a partial d8 octahedral geometry. To better understand the biological activities, molecular docking calculations against the PBP2a proteins from S. aureus, OmpK36 proteins from K. pneumoniae, and DHPS proteins were also carried out. According to the results, the active nickel complexes should have had better activity than the control drug AgSD, however their activity was decreased due to solubility issues.

Dihydrogen evolution was observed in a two‐step protonation reaction starting from a Ni0 precursor with a tripodal N‐heterocyclic carbene (NHC) ligand. Upon the first protonation, a NiII monohydride complex was formed, which was isolated and fully characterized. Subsequent protonation yields H2 via a transient intermediate (INT) and an isolable NiII acetonitrile complex. The latter can be reduced to regenerate its Ni0 precursor. The mechanism of H2 formation was investigated by using a deuterated acid and scrutinized by 1H NMR spectroscopy and gas chromatography. Remarkably, the second protonation forms a rare nickel dihydrogen complex, which was detected and identified in solution and characterized by 1H NMR spectroscopy. DFT‐based computational analyses were employed to propose a reaction profile and a molecular structure of the Ni−H2 complex. Thus, a dihydrogen‐evolving, closed‐synthetic cycle is reported with a rare Ni−H2 species as a key intermediate. [ABSTRACT FROM AUTHOR]

A new method has been proposed for the synthesis of bis(phosphine sulfides) and nickel and platinum chelate complexes of 1,3,6-azadiphosphacycloheptanes. The method is based on the ability of 14-membered 3,6,10,13-diazadiphosphacyclotetradecanes to undergo a reversible transformation in solutions into a mixture of meso- and rac-isomers of seven-membered bis-phosphines. The reaction of 3,6,10,13-diazadiphosphacyclotetradecanes with elementary sulfur results in 14-membered tetrakis(phosphine sulfides) or seven-membered bis(phosphine sulfides), depending on the reaction conditions. The reaction of 1,3,6-azadiphosphacycloheptanes, resulting from the reversible dissociation of 14-membered tetraphosphines in chloroform, with Ni(CH3CN)6(BF4)2 and Pt(COD)Cl2 gives the corresponding chelate complexes. The structures of the meso-isomer of 1-cyclohexyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane-3,6-disulfide, bis-(κ2-1-isopropyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane)nickel bis(tetrafluoroborate), bis-(κ2-1-cyclohexyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane)chloronickel tetrafluoroborate, and cis-dichloro-(κ2-1-cyclohexyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane)platinum(II), isolated in crystalline form, have been confirmed by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

Reaction of Ni(CH3COO)2·4H2O with monoethanolamine (HMEA), in the presence of NaClO4, generates a mixed-anion complex, fac-[Ni(HMEA)3](ClO4)(CH3COO) (1). Compound 1 has been characterized by single crystal X-ray diffraction, IR and UV-VIS spectroscopy. The analysis of the crystal packing reveals the presence of an extended network supported by hydrogen bonds established between the anions and the complex cations. [ABSTRACT FROM AUTHOR]

[Display omitted] Readily available air-stable (NHC)NiCp 2 complexes (NHC is N-heterocyclic carbene, Cp is cyclopentadienyl anion ligand) can be used as efficient thermally activated precatalysts for hydroheteroarylation of olefins with various heteroarenes. According to preliminary mechanistic studies, precatalyst activation may involve reductive elimination of two Cp ligands to give 1,1"-bi(cyclopenta-2,4-diene) and (NHC)Ni0 active species under elevated temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] Density-functional theory (DFT) calculations at B3LYP/6-311+G(df,p) and M06/6-311+G(df,p) levels of theory predict the stability of new polynuclear sandwich complexes [Cu 5 (C 10 H 10) 2 ]+ and Ni 5 (C 10 H 10) 2 based on flat [10]annulene cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] A simple one-step synthesis of (NHC) 2 NiCl 2 complexes containing bulky N-heterocyclic carbene (NHC) ligands relies on the C–H metallation of N , N' -diaryl-substituted azolium salts, NHC-precursors, with NiCl 2 Py 2 in the presence of Cs 2 CO 3 and pyridine. This procedure allows one to implement all synthetic manipulations in air. [ABSTRACT FROM AUTHOR]

Urease is an enzyme containing a dinuclear nickel active center responsible for the hydrolysis of urea into carbon dioxide and ammonia. Interestingly, inorganic models of urease are unable to mimic its mechanism despite their similarities to the enzyme active site. The reason behind the discrepancy in urea decomposition mechanisms between inorganic models and urease is still unknown. To evaluate this factor, we synthesized two bis-nickel complexes, [Ni2L(OAc)] (1) and [Ni2L(Cl)(Et3N)2] (2), based on the Trost bis-Pro-Phenol ligand (L) and encompassing different ligand labilities with coordination geometries similar to the active site of jack bean urease. Both mimetic complexes produced ammonia from urea, (1) and (2), were ten- and four-fold slower than urease, respectively. The presence and importance of several reaction intermediates were evaluated both experimentally and theoretically, indicating the aquo intermediate as a key intermediate, coordinating urea in an outer-sphere manner. Both complexes produced isocyanate, revealing an activated water molecule acting as a base. In addition, the reaction with different substrates indicated the biomimetic complexes were able to hydrolyze isocyanate. Thus, our results indicate that the formation of an outer-sphere complex in the urease analogues might be the reason urease performs a different mechanism. [ABSTRACT FROM AUTHOR]

Although the metal‐based catalyzed cyanomethylation of aldehydes is well‐developed, a similar approach to ketones with acetonitrile derivatives remains a challenge. Thanks to Tolman type complexes, NiII‐complexes with a pyridine(dicarboxamide) pincer ligand, an alternative metal‐catalyzed (1–5 mol% catalyst) cyanomethylation of an array of isatins and activated ketones is reported at room temperature. High isolated yields (up to 99%) were obtained not only with the poorly acidic acetonitrile but also with more challenging substituted alkyl cyanide nucleophiles. The in situ generated putative ion paired catalysts [NiCR2CN]−Cat+ likely benefit from the cation part (Cs+ or n‐Bu4N+) to facilitate their formation and catalytic activity. [ABSTRACT FROM AUTHOR]

Reaction of bis(2-picolyl)amine (BPA) with Ni(II) salt yielded [(BPA)NiCl2(H2O)] (NiBPA). The Ni(II) in NiBPA bound to a BPA ligand, two chloride, and one aqua ligands. Because most medications inhibit biological processes by binding to a specific protein, the stopped-flow technique was used to investigate DNA/protein binding in-vitro, and a mechanism was proposed. NiBPA binds to DNA/protein more strongly than BPA via a static quenching mechanism. Using the stopped-flow technique, a mechanism was proposed. BSA interacts with BPA via a fast reversible step followed by a slow irreversible step, whereas NiBPA interacts via two reversible steps. DNA, on the other hand, binds to BPA and NiBPA via the same mechanism through two reversible steps. Although BSA interacts with NiBPA much faster, NiBPA has a much higher affinity for DNA (2077 M) than BSA (30.3 M). Compared to NiBPA, BPA was found to form a more stable BSA complex. When BPA and NiBPA bind to DNA, the Ni(II) center was found to influence the rate but not the mechanism, whereas, for BSA, the Ni(II) center was found to change both the mechanism and the rate. Additionally, NiBPA exhibited significant cytotoxicity and antibacterial activity, which is consistent with the binding constants but not the kinetic stability. This shows that in our situation, biological activity is significantly more influenced by binding constants than by kinetic stability. Due to its selectivity and cytotoxic activity, complex NiBPA is anticipated to be used in medicine. [ABSTRACT FROM AUTHOR]

Novel three nickel(II) complexes of type [Ni(metf)(o-phen)2]Cl2(1), [Ni(metf)(opda)2]Cl2(2), [Ni(metf)(2–2'bipy)2]Cl2(3), (Metf = metformin, o-phen = ortho-phenanthroline, opda = ortho-phenylenediamine, 2–2' bipy = 2–2′ bipyridyl) were synthesized and characterized by various analytical and spectral techniques. Based on these studies, octahedral geometry is assigned to these complexes. The DNA binding properties of these complexes were investigated by absorption, emission, and viscosity studies. From the spectral data, it was concluded that the complexes bind to DNA through groove mode of binding. The intrinsic binding constants (Kb) from absorption spectroscopy were 1.60 × 104, 3.57 × 104, and 5.70 × 104 M−1 for 1, 2, and 3, respectively, and Stern–Volmer quenching constants (Ksv) from emission spectroscopy were 0.11, 0.87, and 0.24, respectively. Thermal degradation pattern of the compounds was studied and Coats–Redfern method is used to determine kinetic parameters for complexes 1, 2, and 3 from thermal studies. The software Discovery Studio 2.1 was used to assess the binding affinity and interaction pattern of complexes with the B-DNA receptor protein and complex 1 has the highest dock score. [ABSTRACT FROM AUTHOR]

The dinuclear nickel(II) complex [Ni2LmClO4] + , where Lm represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, reacts with 5-(4-pyridyl)tetrazole (PyrCN4H) to give the dinuclear complex [Ni2Lm(PyrCN4)]+ . The new complex was both isolated as perchlorate or tetraphenylborate salts and characterised by elemental analysis and IR spectroscopy. The structure of [Ni2Lm(PyrCN4)]BPh4 ⋅ MeCN was determined by single crystal X-ray diffraction, showing that tetrazolate units are in a N2,N3-bridging mode to generate dioctahedral N3Ni(µ-S)2(µ-N4CPyr)NiN3 core.

Dithiocarbamate complexes are of immense interest due to their diverse structural properties and extensive application in various areas. They possess two sulfur atoms that often act as the binding sites for metal coordination in a monodentate, bidentate, or anisodentate fashion. These different coordination modes enhance the possibility for complex formation and make them useful in different areas especially in biomedical fields. A synergy exists in the metal ions and dithiocarbamate moieties, which tends to exert better properties than the respective individual components of the complex. These improved properties have also been attributed to the presence of the C–S bonds. Zinc and nickel ions have been majorly found to bind to the dithiocarbamate in bidentate modes, and consequently different geometries have resulted from this interaction. The aim of this review is to present some studies on the synthesis, structural chemistry, and the relevance of zinc and nickel dithiocarbamates complexes especially in biological systems.

[Display omitted] • A novel method for the development of nickel hydrazone complexes was provided. • Four new nickel hydrazone complexes (1 – 4) were synthesized and characterized. • The catalytic performance of mononuclear and binuclear nickel complexes was compared. The synthesis, characterization, and catalytic activity of four new nickel hydrazone complexes: [NiL 2 ] (1), [Ni(HL) 2 ]·2ClO 4 ·3H 2 O (2), [Ni 2 L 2 (NCS) 2 (H 2 O) 2 ]·2H 2 O (3) and [Ni 2 L 2 (NCNCN) 2 (CH 3 OH) 2 ] (4) were reported here. HL was obtained by mixing 2-acetylpyridine, 2-aminobenzohydrazine, and methanol together. Complexes 1 – 4 were synthesized using HL and nickel perchlorate as the main raw materials, methanol as the solvent, and different auxiliary materials. The four complexes were characterized by FT-IR, UV–Vis, and 1H NMR, and their structures were further confirmed by X-ray single crystal diffraction. The impact of the four complexes on styrene oxidation was assessed by employing H 2 O 2 as the oxidant. Investigations revealed that each complex demonstrated effective catalytic functions. Catalytic activity parameters, such as the ratio of substrate to oxidant, temperature, reaction time, catalyst dosage, solvent dosage, and solvent properties, as well as the effect of acid and base additives, were optimized to obtain better conversion of styrene. In particular, the different catalytic performance between mononuclear and binuclear nickel complexes was compared, and a possible mechanism was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] Five novel NiII-ZnII complexes were prepared from the Schiff base 2-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylphenol. The complexes have been characterized by elemental analysis, IR, UV–Vis spectra. Molecular structures of the complexes have been determined by single crystal X-ray determination. The compounds were evaluated for their antibacterial activities on Bacillus subtilis , Staphylococcus aureus , Escherichia coli and Pseudomonas fluorescens , and antifungal activities on Candida albicans and Aspergillus niger , and gave interesting results. Molecular nanoclusters comprising heterometallic Ni-Zn cores are an interesting class of compounds. In this paper, five novel NiII-ZnII complexes [Ni 2 Zn 2 ClL 3 (HL) 3 ]·0·.25H 2 O (1), [Ni 2 Zn 2 BrL 3 (HL) 3 ]·0·.25H 2 O (2), [Ni 2 Zn 2 Br 2 L 2 (N 3) 2 (MeOH) 2 ]·2MeOH (3), [Ni 2 Zn 2 I 2 L 2 (N 3) 2 (MeOH) 2 ]·2MeOH (4), and [Ni 2 Zn 2 I 2 L 2 (N 3) 2 (DMF) 2 ] (5), were prepared from the Schiff base 2-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylphenol (H 2 L). The complexes have been characterized by elemental analysis, IR, UV–Vis spectra. Molecular structures of the complexes have been determined by single crystal X-ray determination. In complexes 1 and 2 , three of the Schiff bases coordinate to the metal atoms via ether oxygen, imino nitrogen and two phenolate oxygen atoms, while the fourth one coordinates through ether oxygen, imino nitrogen and one phenolate oxygen atoms. In complexes 3 , 4 and 5 , all the donor atoms in the Schiff base ligands participate in coordination. The Ni and Zn atoms in the complexes are in octahedral and trigonal bipyramidal coordination, respectively. The anions of the metal salts and the azide anion, as well as methanol and DMF molecules furnish the coordination sphere. The compounds were evaluated for their antibacterial activities on Bacillus subtilis , Staphylococcus aureus , Escherichia coli and Pseudomonas fluorescens , and antifungal activities on Candida albicans and Aspergillus niger. Interestingly, the complexes have effective activities against Bacillus subtilis and Staphylococcus aureus. [ABSTRACT FROM AUTHOR]

Tris-pyridineoximate iron, cobalt, and nickel(II) pseudoclathrochelates with apical ferrocenyl substituent were obtained in the reasonable yields (50–70%) in a boiling ethanol by the template condensation of 2-acetylpyridineoxime with ferrocenylboronic acid on the corresponding M2+ ion as a matrix. The composition and structure of new ditopic compounds, isolated in the forms of their ionic associates with perchlorate anion, were determined using elemental analysis, UV-vis spectroscopy, MALDI-TOF mass spectrometry, and NMR spectroscopy. According to the magnetometry data, the iron(II) pseudoclathrochelate is a diamagnetic compound, while the temperature dependences of magnetic susceptibility of the nickel and cobalt(II) complexes are characteristic of the high-spin systems with S = 1 and 3/2, respectively. As follows from the X-ray diffraction data for the iron and nickel(II) pseudoclathrochelates, the Ni–N distances (2.15–2.17 Å) are characteristic of the high-spin Ni2+ complexes, while they in its iron(II)-containing analog, slightly exceed of 2 Å, thus suggesting the low-spin state of this ion. [ABSTRACT FROM AUTHOR]

Herein, two nickel(II) complexes [Ni(ntb)(chdc)(CH3OH)]⋅CH3OH⋅3.5H2O (1) and [Ni2(ntb)2(btc)(CH3OH)R]⋅Cl⋅4CH3OH⋅H2O (2) (chdc is trans-1,4-cyclohexanedicarboxylate, btc is 1,3,5-benzenetricarboxylate, ntb is tris(2-benzimidazolylmethyl)amine, R = CH3OH/H2O) containing tetradentate poly-benzimidazole ligand have been synthesized and characterized by FT-IR spectroscopy, UV-Vis spectroscopy, elemental analysis, single‑crystal X‑ray diffraction, and magnetic analysis. X-ray crystallographic analysis shows that the Ni(II) ions in 1 and 2 have distorted octahedral geometries with four nitrogen atoms of ntb, one oxygen atom of carboxylate and one oxygen atom of H2O or CH3OH. Complex 1 is mononuclear with trans-1,4-cyclohexanedicarboxylate coordinated by Ni(II) in monodentate bonding fashion, and complex 2 consists of 1,3,5-benzenetricarboxylato-bridged nickel(II) centers in bis(monodentate) bonding mode. Hydrogen bonds and π–π interactions are important in stabilization of the crystal structures. The variable temperature magnetic susceptibilities of complexes 1 and 2 indicate that there are antiferromagnetic interactions. [ABSTRACT FROM AUTHOR]

A donor‐stabilized silylene 4 featuring a Ni0‐based donating ligand was synthesized. Complex 4 exhibits a pyramidalized and nucleophilic SiII center and shows a peculiar behavior due to the cooperative reactivity of Si and Ni centers. Calculations indicate that the orientation of Ni‐ligands with respect to the silylene moiety is crucial in determining the role of the Ni‐fragment (Lewis acid or Lewis base) towards silylene. Indeed, a simple 90° rotation of the Si−Ni bond, reverses the role of Ni, and transforms a classical silylene→Ni0 complex into an unprecedented Ni0→silylene complex. [ABSTRACT FROM AUTHOR]

The role of ligands in the regulation of the catalytic activity of Ni-complexes (Ni(acac)2) in green process-selective ethylbenzene oxidation with O2 into α-phenyl ethyl hydroperoxide is considered in this article. The dual function of phenol (PhOH) included in the coordination sphere of the nickel complex as an antioxidant or catalyst depends on the ligand environment of the metal. The role of intermolecular H-bonds and supramolecular structures (AFM method) in the mechanisms of selective catalysis by nickel complexes in chemical and biological oxidation reactions is analyzed. [ABSTRACT FROM AUTHOR]

During the controllable synthesis of two vanadium-containing Keggin-type polyoxoniobates (PONbs), [Ni(en)2]5[PNb12O40(VO)5](OH)5·18H2O (1) and [Ni(en)3]5[PNb12O40(VO)2]∙17H2O (2, en = ethylenediamine) are realized by changing the vanadium source and hydrothermal temperature. Compounds 1 and 2 have been thoroughly characterized by single-crystal X-ray diffraction analysis, FT-IR spectra, X-ray photoelectron spectrum (XPS), powder X-ray diffraction (PXRD), etc. Compound 1 contains a penta-capped Keggin-type polyoxoniobate {PNb12O40(VO)5}, which is connected by adjacent [Ni(en)2]2+ units into a three-dimensional (3D) organic-inorganic framework, representing the first nickel complexes connected vanadoniobate-based 3D material. Compound 2 is a discrete di-capped Keggin-type polyoxoniobate {PNb12O40(VO)2} with [Ni(en)3]2+ units as counter cations. Compounds 1 and 2 have poor solubility in common solvents and can keep stable in the pH range of 4 to 14. Notably, both 1 and 2 as electrode materials are active for the selective oxidation of benzyl alcohol to benzaldehyde. Under ambient conditions without adding an alkaline additive, compound 1 as a noble metal free electrocatalyst can achieve 92% conversion of benzyl alcohol, giving a Faraday efficiency of 93%; comparatively, 2 converted 79% of the substrate with a Faraday efficiency of 84%. The control experiments indicate that both the alkaline polyoxoniobate cluster and the capped vanadium atoms play an important role during the electrocatalytic oxidation process. [ABSTRACT FROM AUTHOR]

The new ligand HMeATSM, derived from condensation of 2-3-butanedione with 4-methyl-3-thiosemicarbazide and 2,4-dimethyl-3-thiosemicarbazide, has been synthesized. Its reactivity with nickel(II) and zinc(II) nitrates was explored and the resulting complexes were thoroughly characterized by elemental analysis, conductivity, mass spectrometry, IR, 1H and 13C NMR spectroscopies and their structures were confirmed by single-crystal X-ray diffraction. The results showed that the complex [Ni(MeATSM)]NO3 1 is formed under every reaction condition. In contrast, the reaction with zinc(II) nitrate depends on the temperature and the presence of LiOH·H2O, leading to the obtaining of complexes [Zn(MeATSM)(OH2)](NO3) 2 and [Zn(Me2TS)2(OH2)](NO3)2 3. The crystal structures of complexes 1 and 2 show that the dissymmetric ligand acts as a N2S2 tetradentate monoanionic ligand. The structural preferences of the metals also determine the structure of the complexes: whereas nickel(II) is in a square-planar environment, the zinc atom prefers a distorted square-base pyramid geometry imposed by the coordination mode and the planarity of the bis(thiosemicarbazone) ligand. In contrast, in complex 3, containing two bidentate Me2TS ligands, the Zn(II) is in a trigonal bipyramid arrangement. In all the complexes, the nitrate ion is not coordinated to the metal and acts as a counterion. [ABSTRACT FROM AUTHOR]

A new, cheap, easy-to-synthesize and air-stable photoswitchable nickel(II) complex, QTNiNO2, is reported. The metal centre in QTNiNO2 is coordinated by a nitro group and a [2-methyl-8-aminoquinoline]-1-tetralone ligand. The compound crystallizes in the tetragonal space group I41/a with one complex molecule comprising the asymmetric unit, and the crystals are stable under ambient conditions. Irradiation of the solid-state form of QTNiNO2 with 530–660 nm LED light at 160 K converts the ambidentate nitro moiety fully to the nitrito linkage isomer which is stable up to around 230 K, as indicated by IR spectroscopy measurements. The structures of all species present in the examined crystals and their thermal stability were confirmed via X-ray multi-temperature and photocrystallographic experiments. The impact of temperature on the (photo)isomerization reaction taking place in a single crystal was additionally investigated. The experimental results are supported by computational analyses of crystal packing and intermolecular interactions that influence the isomerization process studied.

The reactions of Ni(OAc)2·2H2O with Schiff base ligands 5-bromo-2-((cyclopentylimino)methyl)phenol (HL1) and 5-bromo-2-(((2-(isopropylamino)ethyl)imino)methyl)phenol (HL2) in methanol afforded two discrete trinuclear complexes [Ni3(L1)2(μ2-η1:η1-OAc)2(DMF)2(BrSal)2] (1) and [Ni3(L2)2(μ2-η1:η1-OAc)2(μ2-η2:η1-OAc)2] (2), where BrSal is the monoanionic form of 4-bromosalicylaldehyde. The complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy. The crystal structures of the complexes have been determined by X-ray crystallography. In both complexes, the nickel atoms are in octahedral coordination geometries. The L1 ligand coordinates to the nickel atoms through the phenolate O and imino N atoms, and the L2 ligand coordinates to the nickel atoms through the phenolate O, imino N and amino N atoms. The antimicrobial activities of the complexes were assayed.

The title compound, [Ni(H2O)6][BaCr(C2O4)3(H2O)3]2·4H2O, was obtained in the form of single crystals from the slow evaporation of an aqueous mixture of {Ba6(H2O)17[Cr(C2O4)3]4}·7H2O and NiSO4·6H2O in the molar ratio 1:4. Its structure is made up of corrugated anionic (101) layers of formula [BaCr(C2O4)3(H2O)3]nn− that leave voids accommodating the charge-compensating cations, [Ni(H2O)6]2+ (point group symmetry \overline{1}), as well as the water molecules of crystallization. The anionic layers are built from the connection of barium and chromium atoms through bridging oxalate ligands. The CrIII atom is hexacoordinated by O atoms of three oxalate ligands while the BaII atom is tenfold coordinated by three O atoms of water molecules and seven O atoms of four oxalate ligands. Each NiII atom sits on an inversion center and is coordinated by six water molecules. One of the uncoordinated water molecules is disordered over two sites, with a refined occupancy ratio of 0.51 (5):0.49 (5). In the crystal, extensive O—H...O hydrogen-bonding interactions link the anionic layers, the charge-balancing cations as well as the water molecules of crystallization into a three-dimensional supramolecular network.

The development of catalysts for the selective hydroxylation of aromatic C–H bonds is an essential challenge in current chemical research. The accomplishment of this goal requires the discovery of powerful metal-based oxidizing species capable of hydroxylating inert aromatic bonds in a selective manner, avoiding the generation of non-selective oxygen-centered radicals. Herein we show an investigation on the ability of nickel(ii) complexes supported by tripodal tetradentate aminopyridine ligands to catalyze the direct hydroxylation of benzene to phenol with H2O2 as oxidant. We have found that modifications on the ligand structure of the nickel complex do not translate into different reactivity, which differs from previous findings for nickel-based arene hydroxylations. Besides, several nickel(ii) salts have been found to be effective in the oxidation of aromatic C–H bonds. The use of fluorinated alcohols as solvent has been found to result in an increase in phenol yield; however, showing no more than two turn-overs per nickel. These findings raise questions on the nature of the oxidizing species responsible for the arene hydroxylation reaction.

The title compound, diaqua[tris(2-aminoethyl)amine]nickel(II) hexaaquanickel(II) bis(sulfate), [Ni(C6H18N4)(H2O)2][Ni(H2O)6](SO4)2 or [Ni(tren)(H2O)2][Ni(H2O)6](SO4)2, consists of two octahedral nickel complexes within the same unit cell. These metal complexes are formed from the reaction of [Ni(H2O)6](SO4) and the ligand tris(2-aminoethyl)amine (tren). The crystals of the title compound are purple, different from those of the starting complex [Ni(H2O)6](SO4), which are turquoise. The reaction was performed both in a 1:1 and 1:2 metal–ligand molar ratio, always yielding the co-precipitation of the two types of crystals. The asymmetric unit of the title compound, which crystallizes in the space group Pnma, consists of two half NiII complexes and a sulfate counter-anion. The mononuclear cationic complex [Ni(tren)(H2O)2]2+ comprises an Ni ion, the tren ligand and two water molecules, while the mononuclear complex [Ni(H2O)6]2+ consists of another Ni ion surrounded by six coordinated water molecules. The [Ni(tren)(H2O)2] and [Ni(H2O)6] subunits are connected to the SO42− counter-anions through hydrogen bonding, thus consolidating the crystal structure.