Search Results (79)

Background/Objectives: First row transition metal ions have recently regained attention in coordination chemistry as alternatives to gadolinium-based paramagnetic contrast agents, motivated by emerging safety concerns associated with certain Gd³⁺-based contrast agents. In this study, we report the development of a novel homoleptic diketonate Fe³⁺ complex functionalized with biocompatible indole moieties. We investigate its potential as a paramagnetic relaxation agent by evaluating its ability to modulate the T₁ and T₂ relaxation times of water proton. Methods: Iron(III) tris-1,3-(1-methylindol-3-yl)propanedionate [Fe(BIP)₃] was synthesized via a thermal method from bis(1-methylindol-3-yl)-1,3-propanedione (HBIP) using Fe(ClO₄)₃∙6 H₂O as the metal source. The complex was characterized by UV-Vis, IR and NMR spectroscopy, differential scanning calorimetry–thermogravimetric analysis, and single-crystal X-ray diffraction. Fe(BIP)₃ aggregation behavior in aqueous environment, including size and morphology of aggregates, was investigated using dynamic light scattering and scanning electron microscopy. Incorporation of the aggregates into phospholipid vesicles was evaluated by fluorescence resonance energy transfer and fluorescence correlation spectroscopy. The paramagnetic properties of monomeric Fe(BIP)₃ were probed in solution by nuclear magnetic resonance recurring to the Evans bulk magnetization method. Results: The designed synthetic procedure successfully afforded Fe(BIP)₃, which was fully characterized by UV-Vis and IR spectroscopy, as well as single-crystal X-ray diffraction. Aqueous solutions of Fe(BIP)₃ spontaneously formed rice-grain-shaped nanoscale aggregates of hydrodynamic radius ≈ 30 nm. Incorporation of these aggregates into phospholipid vesicles enhanced their stability. The longitudinal r₁ and transverse r₂ relaxivities of Fe(BIP)₃ aggregates were assessed to be 1.92 and 52.3 mM⁻¹s⁻¹, respectively, revealing their potential as paramagnetic relaxation agents. Conclusions: Fe(BIP)₃ aggregates, stabilized through incorporation into phospholipid vesicles, demonstrate promising potential as novel paramagnetic relaxation agents in aqueous environments. Full article

We report the synthesis, spectroscopic, structural, and ultrafast photophysical investigation of a series of homoleptic and heteroleptic Zn(II) complexes based on the donor-acceptor β-diketonate ligand 4,4,4-trifluoro-1-phenylbutane-1,3-dione. Mass spectrometry, infrared, and NMR analyses confirm complexation and indicate possible fragmentation pathways involving the sequential loss of β-diketonate ligands. Single-crystal X-ray diffraction revealed that all complexes adopt monomeric octahedral geometries, with the ancillary nitrogen-based ligands introducing variable distortions. Thermal analyses confirmed that the complexes are non-volatile and have an onset >250 °C, with thermal decomposition primarily to ZnO and ZnF₂. Complexes with aromatic Lewis base led to higher residue percentages, likely due to the final graphitic carbon content. UV-Vis absorption and femtosecond transient absorption spectroscopy demonstrate that the chelated β-diketonate ring serves as the main optically active chromophore, a property unaffected by the nitrogen ligands. The free ligand undergoes rapid internal conversion, whereas coordination to Zn stabilizes the triplet state via LMCT, producing long-lived and chemically reactive species relevant to dissociation processes. This study demonstrates how tailored ligand environments can be exploited to tune excited-state properties, offering a rational framework for the design of functional precursors suitable for nonlinear photolysis and advanced nanomaterial synthesis. Full article

The search for bioactive compounds against chronic diseases such as cancer and diabetes includes curcuminoids as promising scaffolds. Here, we report the synthesis of a family of curcuminoid analogue compounds with an extended unsaturated central chain, as follows: difluoroboron complex 1, the enolised curcuminoid 2, and its homoleptic copper complex 3, in moderate to good yields (68–90%). Additionally, their β-cyclodextrin (BCD) association complexes, 4 and 5, were prepared through a mechanochemical method and characterised by spectroscopic techniques. Complete ¹H and ¹³C NMR assignments and NOESY correlations revealed unique solvent effects on the conformational disposition of compound 2, while the copper complex 3 displayed the highest extinction coefficient (1.20 × 10⁵ M⁻¹·cm⁻¹). Furthermore, the authentication of the polymorph of 1 and the new crystal structures of 2 and 3, determined by single-crystal X-ray analysis, were highlighted. Although the copper complex 3 initially exhibited the lowest a-glucosidase inhibitory activity (IC₅₀ > 100 µM), it showed a significant increase (IC₅₀ = 36.27 µM) upon association with BCD, reaching values comparable to the free ligand (IC₅₀ = 45.63 µM). Compounds 1–5 were non-toxic to healthy cells (COS-7), but compound 5 stands out as a promising candidate against this metabolic condition. Full article

First examples of mononuclear homoleptic zinc aminopyridinates have been isolated by reacting the sterically bulky deprotonated 2-aminopyridine ligands, N-(2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridine-2-yl]-amine (1) and N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridine-2-yl]-amine (2) with [Zn{N(SiMe₃)₂}₂]. Single crystal X-ray analyses of the zinc bis(aminopyridinate) complexes (3 and 4) reveal two different orientations of the coordinated ligands most probably due to the steric variation of the of the applied ligands. For 3 not only the two ligands show rare head to head arrangement but also one of the ligand exhibit localized and the other ligand delocalized mode of coordination. In 4 the two ligands adopt the head to tail arrangement for the two coordinated aminopyridinato ligands with anionic function localized at the amido nitrogen atom of both the ligands. NMR tube reactions between equimolar ratios of 1 or 2 and [Zn{N(SiMe₃)₂}₂] show the possible synthesis of the mono(aminopyridnate) Zn amide complexes (5 and 6, respectively) in solution phase, however, the corresponding bis(aminopyridinate) Zn complexes are the selective products. Hirshfeld surface analysis and the two-dimensional fingerprint plots indicate that intermolecular H⋯H contacts and H⋯C/C⋯H π-interactions dominate the crystal packing. Full article

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

The synthesis of [Cu(PteN^˄N)(P^˄P)][BF₄] complexes with pterin-fused phenanthroline (PteN^˄N) derivatives and bisphosphine (P^˄P) co-ligands was achieved through a mechanochemical approach. Due to the extremely poor solubility of PteN^˄N ligands, traditional solution methods are ineffective, whereas solid-state mechanochemistry reliably yielded the targeted heteroleptic—rather than homoleptic—complexes with considerable stability even in solution. The transformation from ligand to complex increased the solubility dramatically. The ligands and complexes were comprehensively characterised with a mixture of routine spectroscopic and spectrometric methods, the applicability of which depended to some extent on the compounds’ solubility, e.g., in the case of NMR spectroscopy. The photophysical properties of the complexes, which were not as exciting as anticipated, were assessed by absorption and emission spectroscopic methods, showing that further improvements are needed in complex design if these species are to be developed towards photocatalysis in the future. Full article

Coordination-driven Cu(I) complexes constitute an interesting class of materials with rich opto-electronic properties and diverse applications. Various homo- and heteroleptic Cu(I) complexes have been reported in the literature. In continuation with our quest for new materials, we report herein two novel coordination-driven self-assembled Cu(I) complexes: the homoleptic (1) and the heteroleptic (2) complexes based on the 6,6′-bis(phenylethynyl)-2,2′-bipyridine (L1) and 2,9-dimethyl-1,10-phenanthroline (dmph) ligands. L1 was prepared by a Pd(II)-catalyzed Sonogashira cross-coupling reaction between phenylactylene and 6,6′-dibromo-2,2′-bipyridine. Homo- and heteroleptic Cu(I) complexes were obtained by the self-assembly of L1 and dmph ligands. Complexes (1) and (2) were obtained in high yields, and are soluble in common organic solvents and stable at room temperature over a long period of time. The optical (absorption and emission) properties of both complexes were evaluated. The optical properties in solution are a function of the ligands and varied for the complexes. Complex (2) was also characterized by single-crystal X-ray diffraction and the intermolecular interaction was studied using Hirschfeld surface analysis. In the solid state, complex (2) exhibited four-coordinate distorted tetrahedral geometry around Cu(I). Density functional theory (B3LYP/6-311++G(d,p) was utilised to determine various molecular descriptors. Full article

The second-order nonlinear optical (NLO) properties of the known heteroleptic complex [Cu(1,10-phenanthroline)xantphos][PF₆] (complex 1) and the related new complexes [Cu(5-NO₂-1,10-phenanthroline)xantphos][PF₆] and [Cu(5-NO₂-1,10-phenanthroline)(dppe)][PF₆] (dppe = 1,2-bis(diphenylphosphino)ethane) (complexes 2 and 3) were investigated in solution by the EFISH (Electric Field-Induced Second Harmonic generation) technique, working at a non-resonant wavelength of 1907 nm. It turned out that they are characterized by large μβ values (957–1100 × 10⁻⁴⁸ esu), much higher than that of the Disperse Red One benchmark. Unexpectedly, the homoleptic complex [Cu(2-mesityl-1,10-phenanthroline)₂][PF₆] (complex 4) shows a similar high second-order NLO response. Quantum chemical calculations based on Density Functional Theory (DFT) methods have been carried out to give insight into the electronic structure of the investigated complexes in relation to NLO properties. This investigation, which represents the first EFISH study on copper(I) complexes, opens a convenient route for the development of low-cost dipolar NLO-active heteroleptic [Cu(P^P)(N^N)][PF₆] and homoleptic [Cu(N^N)₂][PF₆] complexes. Full article

A series of homoleptic rare earth (RE) complexes bearing phosphino-aryloxide ligands (1-RE, 2-La) has been prepared. The complexes have been characterised using multinuclear NMR and IR spectroscopy, X-ray crystallography and elemental analysis. Structural characterisation highlighted the different RE–P interactions as a result of differing Lewis acidity and ionic size across the series, hinting at the possibility of FLP-type activity. The potential reactivity of these complexes has been tested by reacting them with small molecules (H₂, CO, CO₂). A series of side-products (3-RE) has also been observed, isolated and characterised, featuring the incorporation of a phosphonium-aryloxide ligand. Full article

The success of platinum-based chemotherapeutic drugs for clinical cancer treatments has inspired tremendous research efforts on developing new metallic anticancer agents with improved cytotoxic activity and reduced side effects. 2,2′;6′,2″-Terpyridine and its 4′-substituted derivatives have showed great potential as ligand compartments for designing new anticancer drug candidates involving base metals. In this work, we synthesized a series of cobalt and iron coordination compounds based on 4′-pyridyl-2,2′;6′,2″-terpyridine, including homoleptic complexes, a dinuclear bridged complex and 1- and 2-dimensional coordination polymers/networks. The polymorphism of two homoleptic Co^II and Fe^II complexes has been described along with the structural characterization of a Co^II coordination polymer and dinuclear Fe^III complex by X-ray crystallography. These compounds were tested preliminarily as precatalysts for the regioselective hydrosilylation of styrene. Their cytotoxic activities against two human breast cancer cell lines (MCF-7 and MDA-MB 468) and a normal breast epithelial cell line (MCF-10A) were investigated in order to observe the best-performing drug candidates. Full article

The electrochemical oxidation of anodic metals (M = nickel and palladium) in an acetonitrile solution of the thiosemicarbazone ligands (E)-2-(1-(4-methoxyphenyl)ethylidene)-N-methylhydrazine-1-carbothioamide (a), (E)-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (b), and (E)-N-phenyl-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (c) yielded the homoleptic complexes [ML₂], 1a, 1b, 1c, and 2c and [M₄L₄], 2a as air-stable solids. The crystal structures for 1a, 1b, 1c, and 2c show the ligands in a transoid disposition with the [S,S] and [N,N] donor atom pairs occupying cis positions on the nearly square planar coordination plane of the metal. The structure for 2a of S4 symmetry comprises a tetranuclear palladacycle where the metalated ligands are arranged around a central Pd₄S₄ environment: a crown ring with alternating palladium and sulfur atoms. The latter complex is the first example of an electrochemical preparation of a cyclometalated palladium compound, marking a milestone in the chemistry of such species. The compounds have been fully characterized by elemental microanalysis, mass spectrometry, infrared (IR), and ¹H nuclear magnetic resonance (NMR) spectra. Full article

Lung cancer is a leading cause of cancer-related death worldwide that needs updated therapies to contrast both the serious side effects and the occurrence of drug resistance. A panel of non-small cell lung cancer (NSCLC) cells were herein employed as cancer models. Eight structurally related gold(I) and gold(III) complexes with NHC and halides or triphenylphosphane ligands were investigated as lung cancer cell growth inhibitors. As expected, gold compounds with PPh₃ were found to be more cytotoxic than homoleptic [(NHC)₂-Au(I)]X or heteroleptic NHC-Au(I)X or NHC-Au(III)X₃ complexes. Mixed ligand gold(I) compounds exhibiting the linear NHC-AuPPh₃ (compound 7) or the trigonal NHC-Au(Cl)PPh₃ (compound 8) arrangements at the central metal were found to be the best lung cancer cytotoxic compounds. Analysis of the TrxR residual activity of the treated cells revealed that these compounds efficiently inhibit the most accredited molecular target for gold compounds, the TrxR, with compound 8 reaching more than 80% activity reduction in lung cells. Some of the current cancer lung therapy protocols consist of specific lung cancer cell cytotoxic agents combined with antifolate drugs; interestingly, the herein gold compounds are both TrxR and antifolate inhibitors. The human DHFR was inhibited with IC₅₀ ranging between 10–21 µM, depending on substrate concentrations, proceeding by a likely allosteric mechanism only for compound 8. Full article

Curcuminoids are widely studied due to their well-recognized therapeutic properties. These molecules are often derivatized with metals, producing their corresponding homoleptic metal complexes. Numerous crystal structures of homoleptic symmetric curcuminoids with physiologically essential metals are known, although the literature lacks reports of homoleptic metal complexes of unsymmetric curcuminoids (or hemi-curcuminoids) as ligands. Three unknowns must be solved when an unsymmetric curcuminoid ligand is reacted with a metal ion: (a) the degree of coordination (MLn); (b) the spatial geometry; and (c) the conformational nature (syn or anti) of the complex. Herein, we report the structure of the anti-isomer of the Zn complex of the hemi-curcuminoid 5-hydroxy-1-(4-methoxyphenyl)hexa-1,4-dien-3-one. While the NMR shows only one set of signals for this homoleptic complex, the unambiguous stereochemistry was established through single-crystal X-ray diffractometry, revealing an anti-hexacoordinated octahedral ML₂ structure. Full article

A novel tridentate ligand featuring an acridine core and pyrazole rings, namely 2,7- di-tert-butyl-4,5-di(pyrazol-1-yl)acridine, L, was designed and used to create two ruthenium(II) complexes: [RuL₂](PF₆)₂ and [Ru(tpy)L](PF₆)₂. Surprisingly, the ligand adopted different coordination modes in the complexes: facial coordination for the homoleptic complex and meridional coordination for the heteroleptic complex. The electronic absorption and electrochemical properties were evaluated. Although both complexes exhibited favorable electronic properties for luminescence, neither emitted light at room temperature nor at 77 K. This study highlights the complex interplay between ligand design, coordination mode, and luminescence in ruthenium(II) complexes. Full article

The branched complexes of Schiff bases with various iron(III) salts, named G2-[L₂Fe]⁺A⁻ (A⁻ is NO₃⁻, Cl⁻, PF₆⁻), were synthesized using the condensation reaction between carbazole derivatives of salicylic aldehyde and N’-ethylethylenediamine and characterized by various spectroscopic methods (GPC, IR, ¹H NMR, UV/Vis). The studies revealed that the coordination of the two ligand molecules to metal occurs through the nitrogen ions and oxygen atom of azomethine to form a homoleptic system. All the synthesized coordination compounds were examined for their thermal, optical, and magnetic features. Static magnetic measurements showed that only G2-[L₂Fe]Cl was in a single-phase HS state, whereas the Fe(III) ions of G2-[L₂Fe]NO₃ and G2-[L₂Fe]PF₆ at room temperatures were in mixed low-spin (LS, S = 1/2) and high-spin (HS, S = 5/2) states: 58.9% LS/41.1% HS for G2-[L₂Fe]NO₃, 56.1% LS and 43.9% HS for G2-[L₂Fe]PF₆. All G2-[L₂Fe]⁺A⁻ complexes demonstrate antiferromagnetic exchange interactions between neighboring Fe(III) ions. The ground spin state at 2.0 K revealed a Brillouin contribution from non-interacting LS ions and a proportion of the HS Fe(III) ions not participating in AFM interactions: 57%, 18%, and 16% for G2-[L₂Fe]Cl, G2-[L₂Fe]NO₃ and G2-[L₂Fe]PF₆, respectively. EPR measurements confirmed the presence of magnetically active HS and LS states of Fe(III) ions and made it possible to distinguish two HS types-with strong low-symmetry (I-type) and weak, distorted octahedral environments (II-type). It was shown that G2-[L₂Fe]⁺A⁻ complexes are magnetically inhomogeneous and consist of two magnetic sub-lattices: AFM-correlated chains in layers from the I-type HS Fe(III) centers and dynamic short-range AFM ordered LS/II-type HS Fe(III) centers in the paramagnetic phase located between the layers. Full article