Search Results (199)

Redox-active manganese, iron, and nickel complexes of pyridin-2-ylsulfonyl-quinolin-8-yl-amide (psq) provide information for assessing the electronic and structural properties of this new tridentate ligand. Single-crystal X-ray structures show that psq coordinates in a meridional mode with a trigonal geometry for the central deprotonated sulfonamide N donor. With the structures described here, there are now five structures known for hexacoordinated bis-homoleptic complexes of psq. All show the same geometry. No fac isomer, although feasible, has been structurally characterized. The geometrical parameters for [M(psq)₂]^0/+ are surprisingly close to those for archetypical [M(terpy)₂]^2+/3+ (terpy =2,2′:6′,2″-terpyridine) complexes, with octahedral distortion parameters indicating a geometry that is slightly closer to a regular octahedral. The Fe(II) complex, however, bucks this trend, consistent with the magnetic susceptibility measurements indicating a high-spin S = 5/2 state, which stands in contrast to low-spin [Fe(terpy)₂]²⁺. This is rationalized by the trans secondary sulfonamide donors being weaker π acceptors compared to central terpy pyridine donors. An overall two-integer reduced charge for the complexes is consistent with the Co^II/Co^I, M^III/M^II M = Mn, Fe, Co, and Mn^IV/Mn^III redox events being ca. 600–900 mV more cathodic compared to the corresponding events for [M(terpy)₂]²⁺. Full article

Pyrochlore Bi_1.8Mn_0.5Ni_0.5Ta₂O_9-Δ (sp.gr. Fd-3m, a = 10.5038(9) Å) was synthesized by the solid-phase reaction method and characterized by vibrational and X-ray spectroscopy. According to scanning electron microscopy, the ceramics are characterized by a porous microstructure formed by randomly oriented oblong grains. The average crystallite size determined by X-ray diffraction is 65 nm. The charge state of transition element cations in the pyrochlore was analyzed by soft X-ray spectroscopy using synchrotron radiation. For mixed pyrochlore, a characteristic shift of Bi4f and Ta4f and Ta5p spectra to the region of lower energies by 0.25 and 0.90 eV is observed compared to the binding energy in Bi₂O₃ and Ta₂O₅ oxides. XPS Mn2p spectrum of pyrochlore has an intermediate energy position compared to the binding energy in MnO and Mn₂O₃, which indicates a mixed charge state of manganese (II, III) cations. Judging by the nature of the Ni2p spectrum of the complex oxide, nickel ions are in the charge state of +(2+ζ). The relative permittivity of the sample in a wide temperature (up to 350 °C) and frequency range (25–10⁶ Hz) does not depend on the frequency and exhibits a constant low value of 25. The minimum value of 4 × 10⁻³ dielectric loss tangent is exhibited by the sample at a frequency of 10⁶ Hz. The activation energy of conductivity is 0.7 eV. The electrical behavior of the sample is modeled by an equivalent circuit containing a Warburg diffusion element. Full article

The eight new copper(II), nickel(II), zinc(II), and iron(III) coordination compounds [Cu(L)Cl]₂ (1), [Cu(L)Br]₂ (2), [Cu(L)(NO₃)]₂ (3), [Cu(phen)(L)]NO₃ (4), [Ni(HL)₂](NO₃)₂·H₂O (5), [Ni(HL)₂]Cl₂ (6), [Zn(L)₂]·0.125H₂O (7), and [Fe(L)₂]Cl (8), where HL stands for 2-benzoylpyridine 4-allylthiosemicarbazone, were synthesized and characterized. ¹H, ¹³C NMR, and FTIR spectroscopies were used for characterization of the HL thiosemicarbazone. The elemental analysis, the FTIR spectroscopy, and the study of molar electrical conductivity were used for characterization of the coordination compounds 1–8. Also, the crystal structures of HL, its salts ([H₂L]Cl; [H₂L]NO₃), and complexes 1, 3, 5, 7, and 8 were determined using single-crystal X-ray diffraction analysis. Complexes 5, 7, 8 have mononuclear structures, while copper(II) complexes 1 and 3 have a dimeric structure with the sulfur atoms of the thiosemicarbazone ligand bridging two copper atoms together. Thiosemicarbazone HL and the complexes manifest antibacterial and antifungal activities. The studied substances are more active towards Gram-negative bacteria than towards Gram-positive bacteria and fungi. Complex 1 is the most active one towards Gram-positive bacteria and C. albicans, while the introduction of 1,10-phenanthroline into the inner sphere enhances the activity towards Gram-negative bacteria. Thiosemicarbazone and complexes 6 and 7 manifest antiradical activity that exceeds the activity of Trolox. HL and complex 1 manifest antiproliferative activity towards HL-60 cancer cells which exceeds the activity of their analogs with 2-formyl-/2-acetylpyridine 4-allylthiosemicarbazone. Full article

The polymerization of norbornene can occur via ring-opening metathesis polymerization (ROMP) or vinyl-addition pathways, each yielding polynorbornene with distinct structures and properties. This study reports on the synthesis and catalytic application of a new class of vanadium(III) and nickel(II) complexes bearing N-heterocyclic carbene ligands, based on the IPr* framework, for the polymerization of norbornene. The vanadium(III) complexes, activated by diethylaluminum chloride and in the presence of ethyl trichloroacetate, showed activity in ROMP. In contrast, the nickel(II) complexes, activated by methylaluminoxane, exhibited catalytic activity toward vinyl-addition polymerization. Characterization by GPC, NMR, and FTIR confirmed the formation of both ring-opening metathesis polymerization and vinyl-type-derived polynorbornenes, with vinyl-type polymers showing significantly higher molecular weights. Structural variations in the N-heterocyclic carbene ligands, particularly the linker length between imidazole donors, were found to strongly influence polymer molecular weight and the morphology of polynorbornenes. Full article

The reaction of either the L (2S3R) or D (2R3S) enantiomers of H₂N-C*H(R)CO₂⁻ (R = -C*H(OH)CH₃ or -C*H(OH)CH(CH₃)₂) and the L (2S) or D (2R) enantiomers of H₂N-C*H(C(CH3)₂OH)CO₂⁻ with imidazole-4-carboxaldehyde and nickel(II) acetate in methanol yields a single stereoisomer of an oxazolidine. There is retention of chirality on ring positions 4 and 5 (if C_β is chiral) of the oxazolidine, C_α and C_β of the parent amino acid, and transfer of chirality to the newly generated stereogenic centers, ring positions 3, the amino acid nitrogen atom, N_AA, and 2, the aldehyde carbon atom, C_ald. Specifically, when C_α has an S configuration, both N_AA and C_ald are formed as R. Likewise, a C_α which is R results in both N_AA and C_ald being formed as S. For example, the reaction of L threonine (C_α is S and C_β is R) with 4-imidazolecarboxaldehyde in the presence of nickel(II) gives the facial Λ NiL₂, where L is (2R, 3R, 4S, 5R) 4-carboxylato-5-methyl-2-(4-imidazolyl)-1,3-oxazolidine. The same reaction with D threonine produces the enantiomeric Δ complex of (2S, 3S, 4R, 5S) 4-carboxylato-5-methyl-2-(4-imidazoyl)-1,3-oxazolidine. The high stereospecificity is thought to be based on the fused three-ring structure of the characterized nickel complexes in which the hydrogen atoms of C_α, N_AA, and C_ald must be cis to one another. Identical reactions occur with 2-pyridine carboxaldehyde and LT or DT. In contrast, the reactions of L allo threonine (2S3S) and the primary alcohols, L or D serine, give the conventional meridionally coordinated aldimine product. Full article

This study presents the synthesis, physicochemical characterization, and biological evaluation of a novel ternary nickel(II) complex with isoleucine and 1,10-phenanthroline ligands, [Ni(Phen)(Ile)₂]∙6H₂O, designed as a potential antitumor agent. Single-crystal X-ray diffraction revealed a monoclinic structure (C2-space group) with an octahedral Ni(II) coordination involving Phen and Ile ligands. A Hirshfeld surface analysis highlighted intermolecular interactions stabilizing the crystal lattice, with hydrogen bonds (H···H and O···H/H···O) dominating (99.1% of contacts). Density functional theory (DFT) calculations, including solvation effects (in water and methanol), demonstrated strong agreement with the experimental geometric parameters and revealed higher affinity to the water solvent. The electronic properties of the complex, such as HOMO−LUMO gaps (3.20–4.26 eV) and electrophilicity (4.54–5.88 eV), indicated a charge-transfer potential suitable for biological applications through interactions with biomolecules. Raman and infrared spectroscopic studies showed vibrational modes associated with Ni–N/O bonds and ligand-specific deformations, with solvation-induced shifts observed. A study using ultraviolet–visible–near-infrared absorption spectroscopy demonstrated that the complex remains stable in solution. In vitro cytotoxicity assays against MCF-7 (breast adenocarcinoma) and HCT-116 (colorectal carcinoma) cells showed dose-dependent activity, achieving 47.6% and 65.3% viability reduction at 100 μM (48 h), respectively, with lower toxicity to non-tumor lung fibroblasts (GM07492A, 39.8%). Supporting the experimental data, we performed computational modeling to examine the pharmacokinetic profile, with particular focus on the absorption, distribution, metabolism, and excretion properties and drug-likeness potential. Full article

Phenylene-based bis-oxamate polydentate ligands offer a unique opportunity for creating a large variety of coordination compounds, in which paramagnetic metal ions are strongly magnetically coupled. The employment of imino nitroxyl (IN) radicals as supplementary ligands confers numerous benefits, including the strong ferromagnetic interaction between Ni and IN. Furthermore, the chelating IN can act as a capping ligand, thereby impeding the formation of coordination polymers. In this study, we present the molecular and crystal structure and experimental and theoretical magnetic behavior of an exceptional neutral trinuclear complex [Ni(L³⁻)₂(IN)₃]∙5CH₃OH (1) (L is N,N′-1,3-phenylenebis-oxamic acid; IN is [4,4,5,5-tetramethyl-2-(6-methylpyridin-2-yl)-4,5-dihydro-1H-imidazol-1-yl]oxidanyl radical) with a cyclic triangular arrangement. Moreover, in this compound three Ni²⁺ ions are linked by the two bis-oxamate ligands playing a rare tritopic function due to an unprecedented triple deprotonation of the related meta-phenylene-bis(oxamic acid). The main evidence of such a deprotonation of the ligand is the neutrality of the cluster, since there are no anions or cations compensating for its charge in the crystals of the compound. Despite the presence of six possible magnetic couplings in the trinuclear cluster 1, its behavior was reproduced with a high degree of accuracy using a three-J model and ZFS, under the assumption that the three different Ni-IN interactions are equal to each other, whereas only two equivalent-in-value Ni-Ni interactions were taken into account, with the third one being equated to zero. Our study indicates the presence of two opposite-in-nature types of magnetic interactions within the triangular core. DFT and CASSCF/NEVPT2 calculations were completed to support the experimental magnetic data simulation. Full article

A series of para-trifluoromethoxy-substituted and fluorobenzhydryl-functionalized 1,2-bis(imine)acenaphthene ligands: 1-[2,6-{(4-F-C₆H₄)₂CH}₂-4-F₃COC₆H₂N]-2-(ArN)C₂C₁₀H₆ (Ar = 2,6-Me₂C₆H₃ L1, 2,6-Et₂C₆H₃ L2, 2,6-iPr₂C₆H₃ L3, 2,4,6-Me₃C₆H₂ L4, 2,6-Et₂-4-MeC₆H₂ L5), were synthesized and used to generate their corresponding nickel(II) bromide complexes (Ni1–Ni5). Elemental analysis, ¹⁹F NMR, and FT-IR spectroscopy were employed to characterize these five nickel complexes. Single-crystal X-ray diffraction of Ni2 and Ni4 confirmed distorted tetrahedral geometries. Upon activation with either EtAlCl₂ (ethylaluminum dichloride) or EASC (ethyl aluminum sesquichloride), these complexes showed exceptional high activities (up to 22.0 × 10⁶ g PE mol⁻¹ (Ni) h⁻¹) and remarkable thermal stability (4.82 × 10⁶ g PE mol⁻¹(Ni) h⁻¹ at 80 °C) towards ethylene polymerization. The resulting polyethylenes are highly branched, with the type and extent of branches tunable by temperature, solvent, and co-catalyst choice. Moreover, these polymers demonstrated excellent tensile strength (σ_b up to 20.7 MPa) and elastic recovery (up to 58%), characteristic of thermoplastic elastomers (TPEs). These results highlight the dual role of trifluoromethoxy and fluorobenzhydryl groups in enhancing catalytic performance and polymer properties. Full article

A novel S = 1/2 paramagnetic chelating ligand tert-butyl 5-(p-biphenylyl)-2-pyridyl nitroxide (bppyNO) and its S = 1 nickel(II) ion complex [Ni(bppyNO)₂Br₂] were synthesized. X-ray crystallography revealed a 2p–3d–2p heterospin triad, with half of the molecule being crystallographically independent. A relatively planar chelate geometry with the torsion angle ϕ(Ni-O-N-C_2py) = −10.6(5)° at 300 K becomes significantly out-of-plane distorted with ϕ = −46.9(8) and 26.1(11)° at 90 K accompanied by disorder at the oxygen site. The torsion angle changes, Δϕ = 36° and 37°, are among the largest reported for related compounds. Magnetic measurements indicate gradual and incomplete spin transition-like behavior around 143(2) K. A three-state model involving an intermediate-spin (S_total = 1) state is proposed to explain non-zero χ_mT plateau in a low-temperature region. Density functional theory calculations using the determined structures support the proposed mechanism. Furthermore, geometry optimizations assuming S_total = 0, 1, and 2 are in good agreement with the present model. Full article

Antibiotic resistance is a problem repeatedly reported by health authorities. Metalloantibiotics, i.e., biologically active compounds containing one or more metal ions, can be an important resource in the fight against bacteria and fungi. Here, we report the results obtained with a panel of copper(II), nickel(II) and zinc(II) complexes with thiosemicarbazone, semicarbazone and acylhydrazone ligands on Staphylococcus aureus, Escherichia coli and Candida albicans, taken as model systems of human pathogens. To increase the solubility in water, the sulfonic group was introduced on some of the ligands, isolating them as sodium salts (NaH₂L4-NaH₂L7). Complexes 1–14 were isolated, fully characterized and the X-ray structures of 11, 12 and 13 were obtained. While all the ligands have no antimicrobial activity, the copper(II) complexes 1 and 4 and the nickel(II) complex 2, obtained from thiosemicarbazone ligands, showed good activity, in particular against S. aureus; these complexes were investigated in depth, calculating their respective IC₅₀ values (4.2 μM, 3.5 μM and 61.8 μM, respectively). It should be noted that nickel(II) complex 2 does not show hemolytic activity and has a favorable SI value. While all the copper(II) complexes completely degraded the plasmid DNA in presence of H₂O₂, nickel(II) complex 2 cleaved the plasmid DNA leading to the formation of the relaxed nicked conformation, thus suggesting a different mechanism of action. Full article

An electrochemical sensor was developed for the detection of hydrogen peroxide (H₂O₂) based on the in situ formation of a nickel hexacyanoferrate complex on the electrode surface. Screen-printed carbon electrodes were modified with nickel-doped carbon nanodots (Ni-CNDs), and a nickel hexacyanoferrate complex was electrogenerated over the nickel carbon nanodots. Ni-CNDs were synthetized “a la carte” in one step by including nickel (II) acetate as precursor and characterized using different techniques: transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, atomic force microscopy (AFM), and infrared spectroscopy (FTIR). The electrocatalytic activity toward H₂O₂ reduction and the oxidation of the resulting modified electrodes was studied. The developed sensor had a strong electrocatalytic effect on the oxidation and reduction of H₂O₂, yielding detection limits of 3.22 and 0.49 μM, respectively. The H₂O₂ content of a tap water sample was determined, confirming the viability of the developed electrochemical sensor. Full article

Benzimidazoles are considered a promising class of bioactive heterocyclic compounds that show a wide variety of useful biological properties due to their structural similarities to nucleotides such as purines. Among these properties, great attention has been given to the antibacterial activity exhibited by molecules containing a benzimidazole nucleus in their structure since recent research results have shown the potential of such molecules as alternatives in the fight against bacterial resistance. When these compounds have phenylsubstituted groups in the 2-position of the imidazole ring, a series of molecules can be obtained with generally improved pharmacological activity. These types of compounds are suitable for the formation of stable complexes with several transition metals, including nickel and copper; such compounds have also exhibited many biological properties in different reports. Accordingly, this brief review focuses on recent work on the synthesis and characterization of metal complexes of Ni(II) and Cu(II) with ligands derived from 2-(phenylsubstituted) benzimidazole that were subsequently evaluated for antibacterial activity. Full article

In this study, catalytically active coatings on titanium were synthesized by plasma electrolytic oxidation (PEO) in aqueous electrolytes based on sodium tungstate with the addition of sodium phosphate or sodium borate and chelate complexes of iron, cobalt or nickel. Taking into account the EDX, XPS and XRD data, the oxide–phosphate coatings (PWFe, PWCo, PWNi) contained crystalline titanium oxide and amorphous tungstates and/or phosphates of iron triad metals. Amorphization was facilitated by high phosphorus concentrations (up to 6 at.%). Replacing phosphate with borate in the electrolyte with Ni(II)-EDTA complexes led to the crystallization of WO₃ and NiWO₄ in the PEO coatings (BWNi). All formed PEO coatings were active in reactions of the oxidative desulfurization (ODS) of thiophene and dibenzothiophene and oxidative denitrogenation (ODN) of pyridine, as well as in the simultaneous removal of S- and N-containing substrates from their mixture. The stability of samples with MWO₄ increased in the following series: PWNi < PWCo < PW < PWFe < BWNi. Replacing phosphate with borate in the electrolyte resulted in the preparation of catalysts with enhanced stability and activity. In contrast to PWM catalysts, the BWNi catalyst had selectivity toward the oxidation of pyridine in its mixture with thiophene. Full article

Covalent organic frameworks hold great promise for heterogeneous catalysis because of their porous structure for gas adsorption and tunable functionality. Two triazine support materials (MAmPA-COF and MAoPA-COF) were prepared by using melamine as the linked monomer and meta-phthalaldehyde (MPA) or ortho-phthalaldehyde (OPA) as the sub-construction monomer. Two nickel(II) complexes (Ni@MAmPA-COF and Ni@MAoPA-COF) based on the synthesized COFs were prepared to use for ethylene oligomerization. The nickel(II) complexes had good catalytic activities in ethylene oligomerization. Moreover, the substituent position of the aldehyde group in the sub-construction monomer had a certain influence on the specific surface area, morphology and catalytic activity. The morphology of Ni@MAmPA-COF was spherical, while Ni@MAoPA-COF exhibited layered stacking shapes and had a large specific surface area. Ni@MAoPA-COF has a higher catalytic activity and higher selectivity for low-carbon olefins in ethylene oligomerization due to its larger specific surface area and smaller pore width. Ni@MAoPA-COF has good recyclability and still had excellent catalytic activity after three cycles. Based on the gray correlation analysis and single factor experiment, the reaction pressure was the most important factor affecting the activity of Ni@MAoPA-COF in ethylene oligomerization, and the molar ratio of Al/Ni was the main important factor affecting the selectivity. Full article

In our research aimed at replacing precious transition metals like platinum with abundant base metals such as nickel for efficient triplet emitters, we synthesized and studied Ni(II) complexes [Ni(L^NHR)Cl]. These complexes containing the N^C^N cyclometalating dipyridyl-phenide ligand, equipped with pending H-bonding amine groups (NH(C₆H₅) (L^NHPh) and NH(C₆H₅CH₂), ClL^NHBn). Molecular structures determined from experimental X-ray diffractometry and density functional theory (DFT) calculations in the ground state showed marked deviation of the Cl⁻ coligand (ancillary ligand) from the ideal planar coordination, with τ₄ values of 0.35 and 0.33, respectively, along with hydrogen bonding interactions of the ligand NH function with the Cl⁻ coligand. The complexes exhibit long-wavelength absorption bands at approximately 425 nm in solution, with the experimental spectra being accurately reproduced through time-dependent density functional theory (TD-DFT) calculations. Vibrationally structured emission profiles and steady-state photoluminescence quantum yields of 30% for [Ni(L^NHPh)Cl] and 40% for [Ni(L^NHBn)Cl] (along with dual excited state lifetimes in the ns and in the ms range) were found in frozen 2-methyl-tetrahydrofuran (2MeTHF) glassy matrices at 77 K. Furthermore, within a poly(methyl methacrylate) matrix, the complexes showed emission bands centered at around 550 nm within a temperature range from 6 K to 300 K with lifetimes similar to 77 K. Based on TD-DFT potential scans along the metal–ligand (Ni–N) coordinate, we found that in a rigid environment that restricts the geometry to the Franck-Condon region, either the triplet T₅ or the singlet S₄ state could contribute to the photoluminescence. Full article