Search Results (350)

Gold(I) complexes are particularly useful as catalysts in a variety of reactions including, in particular, the electrophilic activation of alkyne substrates, yet they generally require the addition of a silver salt to activate the gold complex by removing an anionic ligand. This results into higher costs and possible problems related to the non-innocence of the silver additive. In this contribution, we highlight the possibility to proficiently use a dinuclear monocationic gold(I) complex developed in our laboratory as a silver-free catalyst. The complex, featuring a bridging N-phosphanyl-N-heterocyclic carbene (NHCP) ligand, indeed exhibits notable activity and selectivity in standard alkyne hydroamination and hydroalkoxylation reactions, particularly in the case of internal alkynes and secondary aromatic amines as substrates. Full article

This study investigates the rational design of a dinuclear zinc(II) coordination polymer, (C₃₆H₃₄Br₂N₈O₄S₂Zn₂), to explore how halogen substitution and ligand choice modulate structural architecture, contributing to the development of functional coordination polymers with tailored properties. The complex was synthesized from a bromo-substituted semicarbazone Schiff base ligand (L1) and a rigid bipyridine linker (L2) under solvothermal conditions, and its structure was elucidated using single-crystal X-ray diffraction (SCXRD), complemented by characterization via powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy. Crystallographic analysis reveals that the complex crystallizes in the triclinic space group P-1, forming discrete dinuclear units where each Zn(II) center adopts a distorted square–pyramidal geometry; these units are extended into one-dimensional chains by bridging L2 ligands and further assembled into a three-dimensional supramolecular network through hydrogen-bonding interactions. PXRD confirms the high phase purity of the bulk material, TGA indicates notable thermal stability up to 130 °C, and IR spectroscopy validates the coordination modes and hydrogen-bonding network. This work elucidates the critical role of the bromo substituent and rigid ancillary ligands in modulating the solid-state structure of the zinc(II) complex. The revealed structure-directing principles provide a valuable reference for the rational design of functional coordination polymers. Full article

Modified electrodes were obtained by immobilizing Mn³⁺ complexes with the following tetraazamacrocycles (1,4,7,10-tetraazacyclododecane ([12]aneN₄), 1,4,8,11-tetrazacyclotetradecane ([14]aneN₄), 1,4,7,11-tetrazacyclotetradecane (iso[14]aneN₄), and 1,4,8,12-tetrazacyclopentadecane ([15]aneN₄) in a Nafion film on the surface of a glassy carbon electrode (GCE). Based on spectroelectrochemical, chronopotentiometric, and chronoamperometric studies, oxidation of mononuclear complexes to dinuclear di-μ-oxo complexes of Mn³⁺ and Mn⁴⁺ was observed, and the mechanism and influence of Nafion on this process were determined. On the basis of voltammetric and chronocoulometric studies, the electroactivity, stability, and diffusion rates of such modified electrodes were demonstrated. Based on voltammetric and chronocoulometric studies, their electrocatalytic properties were analyzed in relation to the oxidation of model compounds used in this type of research, namely, ascorbic acid, glycolaldehyde, and glycolic acid. Full article

Novel copper(II) coordination compounds with hemiaminal N,O-donor ligands were obtained and synthesized in a one-pot reaction from three appropriate substrates (aldehyde, amine, and copper(II) chloride) in methanol. A dinuclear complex with a [Cu₂Cl₂(hemiaminal)₂(amine)₂] coordination mode was obtained. The complex consists of two five-coordinated central Cu(II) cations with square pyramidal geometry and C_i molecular symmetry. The hemiaminal oxygen atom forms a bridge between the two metallic centers, and that coordination bond is a factor stabilizing these hemiaminal moieties, generally regarded as unstable intermediates. We analyzed the energetic and physicochemical properties of the [Cu₂Cl₂(hemiaminal)₂(amine)₂] complex using density functional theory (DFT). First of all, we predicted the geometrical parameters, molecular electrostatic potential, HOMO and LUMO energies, and reactivity indices to indicate the free radical scavenging capacity. Based on the topological analysis of charge densities, we also characterized the properties of hydrogen bonds. Moreover, the antimicrobial properties of the complex were investigated, and it exhibited the highest activity against Gram-positive bacteria and Candida albicans. Full article

Unexpected activation of the tetrabutylammonium cation in the presence of hexachloroplatinate(IV) under light to give a dinuclear complex of trans-μ²:η²,η²-1,3-butadiene-bis(trichloroplatinate(II)) along with a proposed mechanism of the activation has been reported. The mechanism has been investigated using a combination of photodissociation photodetachment mass spectrometry, and frozen-matrix EPR spectroscopy, in addition to 1D and 2D NMR spectroscopy. In addition to the Bu₄N⁺ salts of [PtCl₆]²⁻ that were part of the original observations, the reactivity of Bu₄P⁺, Pr₄N⁺, and Pe₄N⁺ (Pe = pentyl) salts has also been investigated, and, in addition, the possible involvement of η²-butene complex intermediates has been investigated. The combined results provide additional evidence and support for the originally proposed mechanism of activation of the Bu₄N⁺ cation. Full article

Reactions of (pyH)₅[MoOCl₄(H₂O)]₃Cl₂ with picolinic and pyrazinoic acids yielded three new dinuclear molybdenum(V) complexes: (pyH)₂[Mo₂O₄Cl₂(pic)₂]·CH₃CN (1), (pyH)₂[Mo₂O₄Cl₂(pic)₂]·CH₃CH₂CN (2) and (pyH)₂[Mo₂O₄Cl₂(pyraz)₂]·CH₃CN (3) (pic⁻ = picolinate, pyraz⁻ = pyrazinoate and pyH⁺ = protonated pyridine). The compounds were characterized by single-crystal X-ray diffraction, infrared and ¹H NMR spectroscopy, elemental analysis, and TG/DSC measurements. All display a robust {Mo^V₂O₄}²⁺ core with the heteroaromatic ligands bound in a N,O-bidentate chelating manner. Full article

2,2-Bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol (HL) is a heteroscorpionate ligand capable of coordinating metal ions through two nitrogen atoms and one oxygen atom. We report a base free synthetic route to metal complexes of L and explore the resulting structural diversity. Notably, complex composition varies substantially depending on the metal ion, including dinuclear molybdenum species and distinct coordination behavior with silicon and copper. The isolated compounds include the dinuclear, oxygen-bridged complexes (LMoO₂)₂O and (LMoO)(μ-O)₂, as well as the mononuclear complexes LTi(NMe₂)₃, LZrCl₃, LGeCl₃, LWO₂Cl, LCu(acetate)₂H, and LSiMe₂Cl. Single crystal X-ray diffraction reveals that the bulky complex structures generate cavities in the crystal lattice, frequently occupied by solvent molecules. The titanium, zirconium, molybdenum, tungsten, and germanium complexes exhibit octahedral coordination, while structural peculiarities are observed for copper and silicon. The copper(II) complex shows a distorted octahedral geometry with one elongated ligand bond; the silicon complex is pentacoordinated in the solid state. Additional characterization includes melting points, NMR, and IR spectroscopy. The developed synthetic strategy provides a straightforward and versatile route to heteroscorpionate metal complexes. Full article

Pyridinecarbonitriles (pyCN), also referred to as cyanopyridines, are promising ligands for the formation of pyridine-based coordination compounds due to their two different N-donor atoms, which enable versatile coordination modes. Copper(II) complexes containing pyCN derivatives are of particular interest for their potential applications in medicinal chemistry and materials science. In this study, the synthesis, structural characterization, and thermal and magnetic properties of three new copper(II) complexes with 3-pyCN, 4-pyCN, and ethyl picolinimidate, obtained in situ by means of alcoholysis of 2-pyCN, are reported: [Cu₂(μ-Ac)₄(3-pyCN)₂] (1), [Cu(H₂O)₂(Etpic)₂]NO₃ (2), and [Cu(NO₃)₂(CH₃CN)(4-pyCN)₂]·CH₃CN (3). Single-crystal X-ray diffraction confirmed that complex 1 features a dinuclear paddle-wheel structure with bridging acetato ligands and monodentate 3-pyCN molecules, coordinated through the ring nitrogen, while complexes 2 and 3 are mononuclear. Thermal analysis showed an intense and highly exothermic decomposition of complex 3, containing nitrate ligands. Magnetic measurements revealed strong antiferromagnetic coupling in the dinuclear complex 1, whereas complexes 2 and 3 displayed paramagnetic behavior with effective magnetic moments ranging from 1.8 μ_B to 2.0 μ_B, consistent with isolated Cu(II) centers. Full article

A centrosymmetric dinuclear complex, [Dy₂(H₂dapp)₂(μ-OH)₂(H₂O)₂]·4TCNQ·2CH₃OH, was synthesized using the TCNQ^·− radical anion (TCNQ = 7,7,8,8-tetracyanoquino-dimethane) and pentadentate nitrogen-containing Schiff base ligand (H₂dapp = 2,6-diacetylpyridine)-bis(2-pyridylhydrazone). In the Dy₂ dimer, the two Dy^III ions adopt eight-coordinated geometries intermediate between D_4d and D_2d symmetries, linked by two OH⁻ groups, with ferromagnetic Dy-Dy interactions. The TCNQ^·− radical anions are uncoordinated, and they pack tightly into antiparamagnetic dimers to balance the system charge. Under zero field, weak magnetic relaxation was observed, with an approximate Δ_eff = 2.82 K and τ₀ = 6.88 × 10⁻⁶ s. This might be attributed to the short intermolecular Dy···Dy distance of 7.97 Å, which could enhance intermolecular dipolar interactions and quantum tunneling of magnetization (QTM). Full article

To develop single molecule magnets, a dinuclear complex [Dy₂(HOBQ)₄Cl₆] (1) was prepared from the reaction of DyCl₃ with benzo[h]quinolin-10-ol (HOBQ). Each Dy(III) ion shows a compressed octahedral geometry and the two Dy(III) ions in 1 are bridged by two Cl⁻ ligands to construct a dinuclear structure with the four HOBQ ligands on the axial positions and six Cl⁻ ligands in the equatorial plane. Magnetic measurements showed that complex 1 is a field-induced single molecule magnet having an obvious magnetic hysteresis loop with an energy barrier of 71(2) K. These experimental results are corroborated by the ab initio complete active space self-consistent field (CASSCF) calculations which also interpret the magneto-structural correlation. It is a typical example to achieve Dy(III) SMM through regulating coordination geometry, i.e., lengthening equatorial coordination bonds and shortening axial ones to form a compressed octahedral geometry. Full article

Oxidative stress, driven by excess reactive oxygen species (ROS), is a key factor in the progression of neurodegenerative diseases like Alzheimer’s disease (AD). In this context, copper dysregulation can also contribute to this imbalance, being responsible for enhanced ROS production, so that copper scavenging has been investigated as a possible therapeutic strategy. This study investigates the behavior of two isostructural ligands, featuring an N₃O donor set, that effectively chelate Cu(II) in aqueous solution. Interestingly, their resulting mono- or dinuclear copper complexes feature a coordination environment suitable to foster antioxidant activity. By transforming copper’s oxidant potential into antioxidant action, these systems may reduce copper-induced oxidative damage. The work examines the pH-dependent metal-binding behavior of the ligands, the catalytic properties of the resulting complexes under physiological conditions, and their ability to inhibit β-amyloid peptide aggregation. Full article

The synthesis and structural characterization of three new triple-stranded helical complexes ([Dy₂(L²)₃]2Cl∙15H₂O (C1), [Y₂(L²)₃]3(NO₃)Cl∙14H₂O∙DMSO (C2), and [Eu₂(L⁴)₃]∙12H₂O (C3), where L² and L⁴ are ligands derived from pyridoxal hydrochloride and succinic or adipic acid dihydrazides, respectively, were described. The X-ray data, combined with spectroscopic measurements, indicated that L² and L⁴ act as bis-tridentate ligands, presenting two tridentate chelating cavities O,N,O to obtain the dinuclear complexes C1–C3. Their antiviral profile was predicted via in silico calculations in terms of interaction with the structural severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein in the down- and up-states and complexed with the cellular receptor angiotensin-converting enzyme 2 (ACE2). The best affinity energy values (−9.506, −9.348, and −9.170 kJ/mol for C1, C2, and C3, respectively) were obtained for the inorganic complexes docked in the model spike-ACE2, with C1 being suggested as the most promising candidate for a future in vitro validation. The obtained in silico antiviral trend was supported by the prediction of the electronic and physical–chemical properties of the inorganic complexes via the density functional theory (DFT) approach, representing an original and relevant contribution to the bioinorganic and medicinal chemistry fields. Full article

The imidazo[4,5-b]pyridine scaffold, a versatile heterocyclic system, is renowned for its biological and chemical significance, yet its coordination chemistry with biologically relevant metal dications remains underexplored. This study investigates the proton and metal dication affinities of twelve tetracyclic organic molecules based on the imidazo[4,5-b]pyridine core, focusing on their interactions with Ca(II), Mg(II), Zn(II), and Cu(II). Employing a dual approach of electrospray ionization mass spectrometry (ESI-MS) and density functional theory (DFT) calculations, we characterized the formation, stability, and structural features of metal–ligand complexes. ESI-MS revealed distinct binding behaviors, with Cu(II) and Zn(II) forming stable mono- and dinuclear complexes, often accompanied by reduction processes (e.g., Cu(II) to Cu(I)), while Ca(II) and Mg(II) exhibited lower affinities. DFT analysis elucidated the electronic structures and thermodynamic stabilities, highlighting the imidazole nitrogen as the primary binding site and the influence of regioisomeric variations on affinity. Substituent effects were found to modulate binding strength, with electron-donating groups enhancing basicity and metal coordination. These findings provide a comprehensive understanding of the coordination chemistry of imidazo[4,5-b]pyridine derivatives, offering insights into their potential applications in metalloenzyme modulation, metal-ion sensing, and therapeutic chelation. Full article

Through-space charge transfer (TSCT) between spatially adjacent donor and acceptor units has garnered considerable attention as a promising design principle for optoelectronic materials. While TSCT systems incorporating rigid spacers have been extensively studied to enhance through-space interactions, transition metal complexes connected by flexible linkers remain underexplored, despite increasing interest in their potential TSCT behavior. Herein, we report the design and synthesis of a donor–acceptor–donor (D-A-D)-type complex (1), in which a central naphthalenediimide (NDI) electron acceptor is linked to 2-phenylpyridinato(salicylaldiminato)platinum(II) complexes via flexible alkyl linkers. By systematically varying the linker length (n = 3, 4, 5, 6; 1a–d), we achieved precise control over the spatial arrangement between the NDI core and the platinum moieties in solution. Notably, compound 1a (n = 3) adopts an S-shaped conformation in solution, giving rise to a distinct TSCT absorption band. The structural and photophysical properties were thoroughly investigated using single-crystal X-ray diffraction, ¹H NMR, NOESY analysis, and DFT calculations, which collectively support the existence of the folded conformation and associated TSCT behavior. These findings highlight that TSCT can be effectively induced in flexible molecular systems by exploiting intramolecular spatial proximity and non-covalent interactions, thereby offering new avenues for the design of responsive optoelectronic materials. Full article

Diphosphine compounds have been used as ligands for a variety of metals, and studies on their structures and reactivities are still of interest. We investigated the coordination chemistry of P–P-bonded diphosphine by conducting reactions of bis(1,1′-dibenzophospholyl) (Db)₂P–P(Db)₂ 1 with d⁰-titanium(IV) reagents. The reaction of 1 with TiCl₄ afforded the dinuclear titanium complex Cl₃Ti{μ-(Db)₂P–P(Db)₂}(μ-Cl)₂TiCl₃ 2. The final structure of titanium complex 2 was determined by single-crystal X-ray structural analysis. The molecular structure of the complex was found to be a dinuclear d⁰-titanium complex coordinated to diphosphine on the same side, and the central titanium atoms were bridged to each other by chlorides. To further elucidate this complex, density functional theory (DFT) calculations were conducted to analyze its structure. Full article