Search Results (52)

Three new hybrid bis(salicylaldiminato)/calix[4]arene ligands H₄L1–H₄L3 have been synthesized and investigated with regard to their coordination behavior toward the UO₂²⁺ cation. The ligands H₄L1 and H₄L2, derived from bis-1,3-amino-ethoxy-functionalized calix[4]arenes and 3-methoxy-2-hydroxy-salicylaldehydes, react readily with uranyl nitrate in the presence of NEt₃ to support mononuclear neutral complexes with a 1:1 metal:ligand stoichiometry, namely [UO₂(H₂L1)] (6) and [UO₂(H₂L2)] (7). Ligand H₄L3, with an additional alanyl linker connecting the bis(2-amino-ethoxy)-calix[4]arene backbone and the 3-methoxy-2-hydroxy-salicylaldehyde arms, supports a neutral, mixed-ligand dinuclear uranyl complex [(UO₂)₂(MeO)₂(H₂L3)] (8). The ligands H₄L1 and H₄L2 act as pentadentate O₄N ligands for the UO₂²⁺ ion to produce a distorted pentagonal bipyramidal coordination environment (O₆N donor set). The ligand H₄L3 supports a binuclear [UO₂(μ-OMe)₂UO₂]²⁺ core unit, whose terminal coordination sites are occupied by the donors of the two pendant arms of H₄L3. The spectroscopic properties (NMR, IR, UV-Vis, ESI-MS) suggest that the complexes 6 and 7 retain their integrity in solution state. The structures are further stabilized by intramolecular hydrogen bonding interactions, as implied by computational analyses (NCI plots). These findings provide valuable insight into the influence of spatial flexibility and donor arrangement on the uranyl coordination chemistry of calix[4]arene-based ligand systems. Full article

This study presents a quantitative investigation of substituent effects on the stability of 1:2 complexes formed between para-substituted 2-phenylbenzimidazole ligands and Cu(II) or Co(II) ions. The ligands, featuring hydroxyl (–OH), chloro (–Cl), and nitro (–NO₂) substituents, were synthesized via copper acetate-mediated oxidative cyclization. Stability constants (log K) were determined spectrophotometrically using both the Benesi–Hildebrand and Job methods, which yielded perfectly consistent results and confirmed ML₂ stoichiometry. For both metal series, the stability decreases in the order –OH > –Cl > –NO₂. Excellent linear correlations were obtained between log K and Hammett σ constants, yielding reaction constants of ρ = −0.79 for Cu(II) and ρ = −1.00 for Co(II). These negative ρ values confirm that electron-donating substituents enhance complex stability by increasing electron density on the donor nitrogen. Furthermore, the stability constants for Cu(II) complexes are approximately two orders of magnitude higher than those for Co(II), in agreement with the Irving–Williams series. This work establishes a clear, predictive structure–stability relationship and validates the combined methodological approach for quantifying metal–ligand interactions in tunable benzimidazole systems. Full article

The complexes cis-[Ru(dmbpy)₂Cl(bpy)](PF₆) (Rubpy) and cis-[Ru(dmbpy)₂Cl(bpe)](PF₆) (Rubpe) (dmbpy = 4,4′-Dimethyl-2,2′-dipyridyl, bpy= 4,4′-dipyridyl and bpe = 1,2-bis(4-pyridyl)ethane) were synthesized and spectroelectrochemically characterized. Both Ru(II) complexes exhibited absorption bands assigned to intraligand and metal-to-ligand charge transfer (MLCT) transitions, and their spectral stability in PBS buffer (pH 7.4) supports their suitability for biological studies involving biomolecules or living cells. Fluorescence quenching assays revealed strong interactions with bovine serum albumin (BSA), with binding constants (K_b) values were 2.89 × 10⁵ M⁻¹ for Rubpy and 1.97 × 10⁵ M⁻¹ for Rubpe, and a stoichiometry of one binding site per albumin molecule. DNA-binding studies demonstrated non-covalent interactions with ss-DNA, evidenced by a hyperchromic effect in the MLCT bands, suggesting a partial intercalation or groove-binding mechanism. Cellular uptake assays indicated moderate incorporation of both complexes in tumor cells, with uptake levels of 52% (Rubpy) and 47% (Rubpe) in HeLa cells, and 42% (Rubpy) and 32% (Rubpe) in MDA-MB-231 cells. Despite the similar uptake profiles, cytotoxicity assays showed that Rubpe is approximately 2.4 times more potent than Rubpy, with IC₅₀ values of 9 μM (HeLa) and 12 μM (MDA-MB-231), compared to 22 μM and 29 μM for Rubpy, respectively. These results highlight the relevance of these Ru(II) complexes as molecular platforms for exploring structure–activity relationships in anticancer agents. Full article

The synthesis, characterization, and equilibrium studies of complexes of selected lanthanide ions Eu(III), Gd(III), and Tb(III) with the ligand 1,3-bis(3-bromo-5-chlorosalicylideneamino)-2-propanol (H₃L) are reported. It was found that in the solid state, the complexes with the formulas [Eu(H₃L)₂(NO₃)₃], [Gd(H₃L)₂(NO₃)₃], and [Tb(H₃L)₂(NO₃)₃] are formed. In solution, complexes with stoichiometries of Ln(III):H₃L 1:1 and 1:2 were obtained. The ligand H₃L was isolated in crystalline form, and its molecular structure and conformation were determined by single-crystal X-ray diffraction analysis. The compounds were further characterized by elemental analysis, infrared spectroscopy, ¹H NMR, ¹³C NMR techniques, and mass spectrometry (ESI), confirming the formation of the Schiff base group. Stability constants of the complexes in solution were determined using potentiometric titration, providing insights into the metal-ligand binding equilibria. In addition, the spectroscopic properties of the ligand and its lanthanide(III) ion complexes were investigated by UV-Vis spectroscopy, which confirmed ligand-to-metal charge transfer interactions, as well as by luminescence measurements. The luminescence studies revealed inefficient energy transfer in [Eu(H₃L)₂(NO₃)₃] complexes, while no transfer was observed in [Tb(H₃L)₂(NO₃)₃] systems at any pH value. This behavior is attributed to the large energy gap between the ligand triplet state and the lowest resonant levels of the studied lanthanide ions. Full article

A series of silver-polygalacturonate complexes with improved structure and activity against bacterial infections was developed. Pure sodium polygalacturonate was obtained by saponification of a pectin precursor and identified by NMR as predominantly homogalacturonan (uronide content 95%). Polygalacturonate complexes with ionic and borohydride-reduced silver with a controllable metallic component were synthesized; the role of spontaneous Ag⁺ reduction was revealed. The presence of uniform 5 nm nanoparticles and negligible particulate by-products in the reduced complexes was verified. The complexes showed similar silver-normalized activity against non-resistant bacteria, irrespective of complex stoichiometry/silver state. Pharmaceutical silver proteinate with a similar nanoparticle profile exhibited the same silver-normalized activity, indicating the lack of a ligand effect. The Ag⁺ complex was more effective against some hospital drug-resistant strains. The cytotoxicity of the complexes depended on fibroblast type, silver state, ligand type, exposure time, presumably in association with cellular availability and glutathione depletion. The complexes were administered to rats with excisional wounds persistently infected with S. aureus. Swab/histological analyses of the treated wounds revealed decreased bacterial burden/tissue damage, along with promotion of wound contraction/closure and matrix formation. The nanoparticle complexes that were compared had similar antibacterial/regenerative effects, while the Ag⁺ complex demonstrated higher efficacy in vivo. These results encourage the use of the developed silver-polygalacturonate complexes as antibacterial substances. Full article

This study presents the synthesis and physicochemical characterization of coordination compounds formed between chrysin, a natural flavonoid, and transition metal ions: Mn(II), Co(II), and Zn(II). The complexes were obtained under mildly basic conditions and analyzed using elemental analysis, thermogravimetric analysis (TGA), silver-assisted laser desorption/ionization mass spectrometry (SALDI-MS), FT-IR spectroscopy, and ¹H NMR. The spectroscopic data confirm that chrysin coordinates as a bidentate ligand through the 5-hydroxyl and 4-carbonyl groups, with structural differences depending on the metal ion involved. The mass spectrometry results revealed distinct stoichiometries: 1:2 metal-to-ligand ratios for Mn(II) and Co(II), and 1:1 for Zn(II), with additional hydroxide coordination. Biological assays demonstrated that Co(II) and Mn(II) complexes exhibit enhanced antibacterial and anti-biofilm activity compared to free chrysin, particularly against drug-resistant Staphylococcus epidermidis, whereas the Zn(II) complex showed negligible biological activity. Full article

We report an investigation on the cobalt(II) chelation mechanism by a modified α-maltoside ligand 9 decorated with two iminodiacetate (IDA) residues on C6,C6′ positions. Herein we uncovered the capacity of this biodegradable ligand to chelate cobalt(II), an ionic metal contaminant in the environment that is used, in particular, in lithium-ion batteries. The interactions between cobalt(II) and synthesized ligand 9 were systematically studied using different analytical methods such as ¹H and ¹³C NMR, potentiometry, spectrophotometry, ITC, and ICP-AES. We observed a high affinity for the 1:1 complex, one cobalt(II) associated with two iminodiacetate groups, which is 10-fold higher than the 2:1 complex, where each of the two IDA groups interacts alone with a cobalt(II). Taking into account the log β_CoL value obtained (≈12.3) with the stoichiometry 1:1, the strength of this complexation with cobalt(II) can be ranked as follows for the most common ligands: IDA < MIDA < NTA < 9 < EDTA < TTHA < DTPA. We further completed a preliminary remediation test with water contaminated with cobalt(II) and recovered cobalt(II) metal using Chelex^® resin, which allowed a recycling of the synthetic ligand for future recovering experiments. The results shed light on the great potential of using this synthetic ligand as an effective and green remediation tool. Full article

Lanthanide-based metal–organic frameworks (Ln-MOFs) represent a key material in various optical applications. Thus, they offer the possibility of fine-tuning their functional properties by adjusting the composition, stoichiometry, and ligand nature. This work reports for the first time the environmentally friendly one-pot synthesis of Eu-Tb-doped yttrium-1,3,5-benzenetricarboxylate MOF, i.e., Y-BTC: Eu (10%), Tb (10%), under mild conditions of temperature and pressure. Structural and morphological investigations were conducted through ATR-IR, XRD, and FE-SEM characterization. The doping percentage was analyzed by EDX spectroscopy. The luminescence properties confirm the down-shifting behavior of the MOF, paving the way for using this Eu-Tb-doped Y-BTC system in photovoltaic technology. Full article

The complexation behavior of lanthanide(III) ions with terephthalic acid (1,4-benzene-dicarboxylic acid) in 0.01 M KNO₃ aqueous solutions was studied across a broad pH range and at two metal-to-ligand ratios using potentiometric titration combined with photoluminescence spectroscopy. Chemometric analysis of titration curves enabled the determination of relative molar fractions, stability constants, and probable stoichiometry of the formed complexes. In solutions with a 1:2 metal-to-ligand ratio, bis-complexes (two terephthalate ligands per lanthanide ion) predominated, while ligand-rich conditions favored the formation of tetra-complexes (four ligands per metal ion). In alkaline media, bis-complexes transform into mixed hydroxy-terephthalate species. Meanwhile, for the tetra-complexes, the addition of NaOH results in the formation of lanthanide ion hydroxo complexes without organic ligands. The structural diversity of these complexes, driven by the terephthalate ligand’s tendency to maximize denticity, suggested dimeric or oligomeric configurations. The stability constants and structural features of complexes in solution were found to align with those of known solid-state lanthanide–terephthalate polymers, highlighting their potential as models for polymeric structures. Full article

The food industry uses indigo carmine (IC) extensively as a blue colorant to make processed food for young children and the general population more attractive. Given that IC can act as a ligand, this raises concerns about its interactions with essential metal ions in the human body. In view of this interest, in the present investigation, the copper(II)/indigo carmine system was thoroughly investigated in aqueous solution and in the solid state, and the detailed structural characterization of the complexes formed between copper(II) and the ligand was performed using spectroscopic methods, complemented with DFT and TD-DFT calculations. NMR and UV/Vis absorption spectroscopy studies of the ligand in the presence of copper(II) show changes that clearly reveal strong complexation. The results point to the formation of complexes of 1:1, 1:2 and 2:1 Cu(II)/IC stoichiometry in aqueous solution, favored in the pH range 6–10 and stable over time. DFT calculations indicate that the coordination of the ligand to the metal occurs through the adjacent carbonyl and amine groups and that the 1:1 and the 2:1 complexes have distorted tetrahedral metal centers, while the 1:2 structure is five-coordinate with a square pyramidal geometry. FTIR results, together with EDS data and DFT calculations, established that the complex obtained in the solid state likely consists of a polymeric arrangement involving repetition of the 1:2 complex unit. These results are relevant in the context of the study of the toxicity of IC and provide crucial data for future studies of its physiological effects. Although the general population does not normally exceed the maximum recommended daily intake, young children are highly exposed to products containing IC and can easily exceed the recommended dose. It is, therefore, extremely important to understand the interactions between the dye and the various metal ions present in the human body, copper(II) being one of the most relevant due to its essential nature and, as shown in this article, the high stability of the complexes it forms with IC at physiological pH. Full article

A systematic study has been conducted on barbiturate complexes of all five alkali metals, Li–Cs, prepared from metal carbonates or hydroxides in an aqueous solution without other potential ligands present, varying the stoichiometric ratio of metal ion to barbituric acid (BAH). Eight polymeric coordination compounds (two each for Na, K, and Rb and one each for Li and Cs) have been characterised by single-crystal X-ray diffraction. All contain some combination of barbiturate anion BA⁻ (necessarily in a 1:1 ratio with the metal cation M⁺), barbituric acid, and water. All organic species and water molecules are coordinated to the metal centres via oxygen atoms as either terminal or bridging ligands. Coordination numbers range from 4 (for the Li complex) to 8 (for the Cs complex). Extensive hydrogen bonding plays a significant role in all the crystal structures, almost all of which include pairs of N–H···O hydrogen bonds linking BA⁻ and/or BAH components into ribbons extending in one dimension. Factors influencing the structure adopted by each compound include cation size and reaction stoichiometry as well as hydrogen bonding. Full article

Redox non-innocent ligands react with metal precursors to form complexes where the oxidation states of the ligand and thus the metal atom cannot be easily defined. A well-known example of such ligands is bis(o-aminophenol) N,N′-bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine, previously developed by the Wieghardt group, which has a potentially tetradentate coordination mode and four distinct protonation states, whereas its electrochemical behavior allows for five distinct oxidation states. This rich redox chemistry, as well as the ability to coordinate to various transition metals, has been utilized in the syntheses of metal complexes with M₂L, ML and ML₂ stoichiometries, sometimes supported with other ligands. Different oxidation states of the ligand can adopt different coordination modes. For example, in the fully oxidized form, two N donors are sp²-hybridized, which makes the ligand planar, whereas in the fully reduced form, the sp³-hybridized N donors allow the formation of more flexible chelate structures. In general, the metal can be reduced during complexation, but redox processes of the isolated complexes typically occur on the ligand. Combination of this non-innocent ligand with redox-active transition metals may lead to complexes with interesting magnetic, electrochemical, photonic and catalytic properties. Full article

The aim of this work is to explore a new library of coordination compounds for medicinal applications. Gallium is known for its various applications in this field. Presently, indium is not particularly important in medicine, but it shares a lot of chemical traits with its above-mentioned lighter companion, gallium, and is also used in radio imaging. These metals are combined with thiosemicarbazones, ligating compounds increasingly known for their biological and pharmaceutical applications. In particular, the few ligands chosen to interact with these hard metal ions share the ideal affinity for a high charge density. Therefore, in this work we describe the synthesis and the characterization of the resulting coordination compounds. The yields of the reactions vary from a minimum of 21% to a maximum of 82%, using a fast and easy procedure. Nuclear Magnetic Resonance (NMR) and Infra Red (IR) spectroscopy, mass spectrometry, elemental analysis, and X-ray Diffraction (XRD) confirm the formation of stable compounds in all cases and a ligand-to-metal 2:1 stoichiometry with both cations. In addition, we further investigated their chemical and biological characteristics, via UV-visible titrations, stability tests, and cytotoxicity and antibiotic assays. The results confirm a strong stability in all explored conditions, which suggests that these compounds are more suitable for radio imaging applications rather than for antitumoral or antimicrobic ones. Full article

The prediction of the metal cluster within a coordination polymer or complex, as well as the dimensionality of the resulting polymer or complex (i.e., 0D, 1D, 2D, or 3D), is often challenging. This is the case for Ph₂P(CH₂)_mPPh₂ ligands (1 ≤ m ≤ 8) and CuX salts, particularly for X = I. This work endeavors a systematic statistical analysis combining studies in the literature and new data, mapping the nature of the resulting CuI aggregates with eight different diphoshphines in 2:1, 3:2, 1:1, 2:3, and 1:2 CuI:Ph₂P(CH₂)_mPPh₂ molar ratios as a function of m, which lead to either pure products or mixtures. Several trends are made relating stoichiometry and chain length to the CuI cluster formed (i.e., globular vs. quasi-planar). Four new X-ray structures were determined: [Cu₃I₂(L1)₃]I, Cu₃I₃(L2)₂, Cu₂I₂(L6)₂, and Cu₄I₄(L8)₂, where m is, respectively, 1, 2, 6, and 8, in which the Cu_xI_y central aggregates adopt triangular bipyramid, diamond, rhomboid, and cubane shaped motifs, respectively. Photophysical measurements assisted the establishment of trends considering the paucity of the crystallographic structures. During this study, it was also found that the 0D-complex Cu₂I₂(Ph₂P(CH₂)₅PPh₂)₂ exhibits thermally activated delayed fluorescence. Full article

Bearing in mind the interest in the development and application of amino acids/peptides as bioinspired systems for sensing, a series of new phenylalanine derivatives bearing thiosemicarbazone and hydrazone units at the side chain were synthesised and evaluated as fluorimetric chemosensors for ions. Thiosemicarbazone and hydrazone moieties were chosen because they are considered both proton-donor and proton-acceptor, which is an interesting feature in the design of chemosensors. The obtained compounds were tested for the recognition of organic and inorganic anions (such as AcO⁻, F⁻, Cl⁻, Br⁻, I⁻, ClO₄⁻, CN⁻, NO₃⁻, BzO⁻, OH⁻, H₂PO₄⁻ and HSO₄⁻) and of alkaline, alkaline-earth, and transition metal cations, (such as Na⁺, K⁺, Cs⁺, Ag⁺, Cu⁺, Cu²⁺, Ca²⁺, Cd²⁺, Co²⁺, Pb²⁺, Pd²⁺, Ni²⁺, Hg²⁺, Zn²⁺, Fe²⁺, Fe³⁺ and Cr³⁺) in acetonitrile and its aqueous mixtures in varying ratios via spectrofluorimetric titrations. The results indicate that there is a strong interaction via the donor N, O and S atoms at the side chain of the various phenylalanines, with higher sensitivity for Cu²⁺, Fe³⁺ and F⁻ in a 1:2 ligand-ion stoichiometry. The photophysical and metal ion-sensing properties of these phenylalanines suggest that they might be suitable for incorporation into peptide chemosensory frameworks. Full article