Search Results (13)

Background: 8-Quinolinol and its derivatives are drawing significant attention across various disciplines due to their remarkable versatility. These compounds are well-known for their exceptional chelating ability, forming stable metal complexes via their nitrogen and oxygen electron donor atoms. This main characteristic determines their broad utility. Biological activity can also be explained by the chelating capacity, which allows 8-quinolinol to bind to essential metal ions such as Fe, Zn, Cu, and others. This chelation disrupts metal-dependent biological processes in target cells or organisms, leading to a range of effects, including antimicrobial, anticancer, antifungal, and neuroprotective activities. On the other hand, the biological activity of pyrazole derivatives is attributed to their heterocyclic structure, which allows for interactions with biological targets that can lead to enzyme inhibition, receptor antagonism, radical scavenging, and other effects. Objective: This work aimed to synthesize and characterize novel diazene compounds derived from 8-quinolinol or 2-methyl-8-quinolinol and pyrazole amines, and to evaluate their antimicrobial and anticancer activities. Methods: The compounds have been synthesized by coupling diazonium salts obtained from the diazotization of heterocyclic amines with 8-quinolinol and its derivative, 2-methyl-8-quinolinol. The careful selection of reaction conditions enabled the synthesis of high-purity products. The compounds were characterized by 1D and 2D NMR, FT-IR spectroscopy, UV-Vis spectroscopy, and LC-HRMS analysis. The biological activity of the newly synthesized compounds was evaluated following the protocols of EU-OPENSCREEN, a European Research Infrastructure Consortium (ERIC) initiative dedicated to supporting early drug discovery. Results: By combining diazonium salts obtained from 3-methyl-1H-pyrazol-5-amine and ethyl 5-amino-3-methyl-1H-pyrazole-4-carboxylate with the aforementioned coupling agents, four novel 8-quinolinol derivatives were synthesized. The further hydrolysis of the ethoxy carbonyl functional group allowed its conversion to a carboxylic functional group, thus expanding the series of new compounds to six members. Several compounds from the series have proven to be biologically active against several human pathogenic microorganisms and the Hep-G2 cancer cell line. Conclusions: The combination of two well-known biologically active scaffolds through a classic diazo coupling reaction allowed the synthesis of novel biologically active compounds, which showed promising results as possible antifungal and anticancer agents. These results represent a foundation for future studies, which will include a broader biological screening and in vivo studies. Full article

Transition metal (II) complexes stabilized by 2,6-di(pyrazol-3-yl)pyridine as a novel coplanar tridentate nitrogen-donor ligand have been reported for their unusual structures and photoluminescent properties. In this work, the ligand 2,6-bis(5-isopropyl-1H-pyrazole-3-yl)pyridine (denoted as L) and its transition metal (II) halogenido complexes viz [ZnCl₂(L)] (1), [ZnBr₂(L)] (2), [CuCl₂(L)] (3), and [CuCl(L)(thf)](PF₆) (4) were synthesized and characterized by single crystal X-ray crystal analysis. Its structures contained N–H groups in its pyrazole rings and hydrogen bonds between these N–H donors and the coordinated halogenide ions and lattice solvent molecules. Tautomers between 3-pyridyl and 5-pyridyl substitutes were also observed. In L, the N–H group at the pyrazole nitrogen was located adjacent to the pyridine ring to form hydrogen bonds with adjacent pyrazoles. However, on complexation, the H atoms at the pyrazole nitrogens are shifted remotely to the pyridine. The zinc (II) complexes [ZnCl₂(L)] (1) and [ZnBr₂(L)] (2) possessed distorted trigonal pyramidal structures in the solid state. By comparison, the copper (II) complexes [CuCl₂(L)] (3) and [CuCl(L)(thf)](PF₆) (4) adopted square pyramidal geometry with a Jahn–Teller distortion resulting from their d⁹ electron configurations. Full article

Group 11 metals form with pyrazolate ligand complexes with a general formula of [MPz]_n. The value of “n” varies depending on the type of substituent in the ligand and the metal atom. Copper(I) and silver(I) ions mainly form cyclic di-, tri-, and tetra-nuclear complexes or polymeric structures. Cyclic trinuclear d¹⁰ metal pyrazolates [MPz^m]₃ (M = Cu(I) and Ag(I); Pz = substituted pyrazolate ligand) are of particular interest because their planar structure allows them to form supramolecular aggregates via noncovalent metal–metal, metal–π, and metal–electron donor interactions. Designing complexes based on these interactions has been a focus of research for the last two decades. The ability of cyclic trinuclear copper(I) and silver(I) pyrazolates to form coordination and supramolecular structures determines their properties and potential applications in catalysis, gas sensing, molecular recognition, and photoluminescence. In this review, we discuss noncovalent interactions between cyclic trinuclear silver(I) and copper(I) complexes with various types of ligands. Full article

The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)₂L^F]₂ {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)₂L^F]_n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^F) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)₂L^F]₂ have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand L^F. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)₂L^F]₂, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)₂L^F]₂ and [Ni(hfac)₂L^F]₂, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)₂L^F]₂ showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (J_Mn-ON = −84.1 ± 1.5 cm⁻¹, J_Co-ON = −134.3 ± 2.6 cm⁻¹, and J_Ni-ON = −276.2 ± 2.1 cm⁻¹; $\widehat{H}=-2J{\widehat{\stackrel{⃑}{S}}}_{\mathrm{M}}{\widehat{\stackrel{⃑}{S}}}_{\mathrm{N}\mathrm{O}}$). Notably, the magnetization of [Mn(hfac)₂L^F]₂ having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)₂L^F]_n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {O_NO–Cu(II)–O_NO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (J_Cu-ON = 14.8 ± 0.3 cm⁻¹). Full article

Fosmidomycin (FOS) is a naturally occurring compound active against the 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) enzyme in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, and using it as a template for lead structure design is an effective strategy to develop new active compounds. In this work, by replacing the hydroxamate unit of FOS with pyrazole, isoxazole and the related heterocycles that also have metal ion binding affinity, while retaining the monophosphonic acid in FOS or replacing it with a bisphosphonic acid group, heterocycle-containing mono- and bisphosphonic acid compounds as FOS analogs were designed. The key steps involved in the facile synthesis of these FOS analogs included the Michael addition of diethyl vinylphosphonate or tetraethyl vinylidenebisphosphonate to β-dicarbonyl compounds and the subsequent cyclic condensation with hydrazine or hydroxylamine. Two additional isoxazolinone-bearing FOS analogs were synthesized via the Michaelis–Becker reaction with diethyl phosphite as a key step. The bioactivity evaluation on model plants demonstrated that several compounds have better herbicidal activities compared to FOS, with the most active compound showing a 3.7-fold inhibitory activity on Arabidopsis thaliana, while on the roots and stalks of Brassica napus L. and Echinochloa crus-galli in a pre-emergence inhibitory activity test, the activities of this compound were found to be 3.2- and 14.3-fold and 5.4- and 9.4-fold, respectively, and in a post-emergency activity test on Amaranthus retroflexus and Echinochloa crus-galli, 2.2- and 2.0-fold inhibition activities were displayed. Despite the significant herbicidal activity, this compound exhibited a DXR inhibitory activity lower than that of FOS but comparable to that of other non-hydroxamate DXR inhibitors, and the dimethylallyl pyrophosphate rescue assay gave no statistical significance, suggesting that a different target might be involved in the inhibiting process. This work demonstrates that using bioisosteric replacement can be considered as a valuable strategy to discover new FOS analogs that may have high herbicidal activities. Full article

The redox reactions of various lanthanide metals with 3-(4-pyridyl)pyrazole (4-PyPzH) or 3-(3-pyridyl)pyrazole (3-PyPzH) ligands yield the 2D network ${}_{\infty }^2$[Eu(4-PyPz)₂(Py)₂] containing divalent europium, the 3D frameworks ${}_{\infty }^3$[Ln(4-PyPz)₃] and ${}_{\infty }^3$[Ln(3-PyPz)₃] for trivalent cerium, praseodymium, neodymium, holmium, erbium, and thulium as well as ${}_{\infty }^3$[La(4-PyPz)₃], and the 2D networks ${}_{\infty }^2$[Ln(4-PyPz)₃(Py)] for trivalent cerium and thulium and ${}_{\infty }^2$[Ln₂(4-PyPz)₆]·Py for trivalent ytterbium and lutetium. The 18 lanthanide coordination polymers were synthesized under solvothermal conditions in pyridine (Py), partly acting as a co-ligand for some networks. The compounds exhibit a variety of luminescence properties, including metal-centered 4f–4f/5d–4f emission in the visible and near-infrared spectral range, metal-to-ligand energy transfer, and ligand-centered fluorescence and phosphorescence. The anionic ligands 3-PyPz⁻ and 4-PyPz⁻ serve as suitable antennas for lanthanide-based luminescence in the visible and near-infrared range through effective sensitization followed by emission through intra–4f transitions of the trivalent thulium, holmium, praseodymium, erbium, and neodymium. ${}_{\infty }^2$[Ce(4-PyPz)₃(Py)], ${}_{\infty }^3$[Ce(4-PyPz)₃], and ${}_{\infty }^3$[Ce(3-PyPz)₃] exhibit strong degrees of reduction in the 5d excited states that differ in intensity compared to the ligand-based emission, resulting in a distinct emission ranging from pink to orange. The direct current magnetic studies show magnetic isolation of the lanthanide centers in the crystal lattice of ${}_{\infty }^3$[Ln(3-PyPz)₃], Ln = Dy, Ho, and Er. Full article

A new 1D Ni(II) coordination polymer was synthesized by the reaction of NiSO₄·6H₂O with 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine (BPT) and SCN⁻ as a linker in an acidic medium by heating under reflux conditions. Unusually, the BPT ligand underwent acid-mediated hydrolysis by losing one of the pyrazolyl arms afforded the polymeric [Ni(MPT)(H₂O)(SCN)₂]_n complex (MPT: 4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazin-2-ol. The Ni(II) center is coordinated with one MPT as a bidentate NN-chelate, one water molecule, and two thiocyanate groups in cis positions to one another. One of the thiocyanate groups acts as a bridging ligand between metal centers, leading to a one-dimensional polymeric structure that extends along the c-direction. The other thiocyanate group is terminally N-coordinated. The [Ni(MPT)(H₂O)(SCN)₂]_n complex has been screened in vitro against two pathogenic fungal strains: A. fumigatus, C. albican, and four pathogenic bacterial strains: S. aureus, B. subtilis as gram-positive bacteria, E. coli, P. vulgaris as gram-negative bacteria. The results showed that the complex has the potential to be used as both an antibacterial and an antifungal agent. Also, the [Ni(MPT)(H₂O)(SCN)₂]_n complex showed cytotoxic activities against hepatocellular (HepG-2) and lung (A-549) cell lines, with IC₅₀ values of 132.67 ± 5.14 and 146.97 ± 7.34 μM, respectively. Full article

A series of 18 lanthanide-containing 1D-coordination polymers ¹_∞[Ln₂(2–PyPzH)₄Cl₆], Ln = La, Nd, Sm, dinuclear polymorphic complexes α–, β–[Ln₂(2–PyPzH)₄Cl₆], Ln = Sm, Eu, Gd, α–[Tb₂(2–PyPzH)₄Cl₆], and [Gd₂(2–PyPzH)₃(2–PyPz)Cl₅], mononuclear complexes [Ce(2–PyPzH)₃Cl₃], [Ln(2–PyPzH)₂Cl₃], Ln = Tb, Dy, Ho, and Er, and salt-like complexes [Gd₃(2–PyPzH)₈Cl₈]Cl and [PyH][Tb(2–PyPzH)₂Cl₄] were obtained from the reaction of the respective lanthanide chloride with the 3–(2–pyridyl)pyrazole (2–PyPzH) ligand at different temperatures. An antenna effect through ligand-to-metal energy transfer was observed for several products, leading to the highest luminescence efficiency displayed by a quantum yield of 92% in [Tb(2–PyPzH)₂Cl₃]. The Ce³⁺ ion in the complex [Ce(2–PyPzH)₃Cl₃] exhibits a bright and orange 5d-based broadband emission with a maximum at around 600 nm, marking an example of a strong reduction of the 5d-excited states of Ce(III). The absorption spectroscopy shows ion-specific 4f–4f transitions, which can be assigned to Nd³⁺, Sm³⁺, Eu³⁺, Dy³⁺, Ho³⁺, and Er³⁺ in a wide spectral range from UV–VIS to the NIR region. Full article

Four lanthanide metal-organic frameworks (Ln-MOFs), namely {[Me₂NH₂][LnL]·2H₂O}_n (Ln = Eu 1, Tb 2, Dy 3, Gd 4), have been constructed from a new tetradentate ligand 1-(3,5-dicarboxylatobenzyl)-3,5-pyrazole dicarboxylic acid (H₄L). These isostructural Ln-MOFs, crystallizing in the monoclinic P2₁/c space group, feature a 3D structure with 7.5 Å × 9.8 Å channels along the b axis and the point symbol of {4¹⁰.6¹⁴.8⁴} {4⁵.6}₂. The framework shows high air and hydrolytic stability, which can keep stable after exposed to humid air for 30 days or immersed in water for seven days. Four MOFs with different lanthanide ions (Eu³⁺, Tb³⁺, Dy³⁺, and Gd³⁺) ions exhibit red, green, yellow, and blue emissions, respectively. The Tb-MOF emitting bright green luminescence can selectively and rapidly (<40 s) detect Fe³⁺ in aqueous media via a fluorescence quenching effect. The detection shows excellent anti-inference ability toward many other cations and can be easily recognized by naked eyes. In addition, it can also be utilized as a rapid fluorescent sensor to detect acetone solvent as well as acetone vapor. Similar results of sensing experiments were observed from Eu-MOF. The sensing mechanism are further discussed. Full article

Coinage metal(I)···metal(I) interactions are widely of interest in fields such as supramolecular assembly and unique luminescent properties, etc. Only two types of polynuclear silver(I) pyrazolato complexes have been reported, however, and no detailed spectroscopic characterizations have been reported. An unexpected synthetic method yielded a polynuclear silver(I) complex [Ag(μ-L1Clpz)]_n (L1Clpz⁻ = 4-chloride-3,5-diisopropyl-1-pyrazolate anion) by the reaction of {[Ag(μ-L1Clpz)]₃}₂ with (ⁿBu₄N)[Ag(CN)₂]. The obtained structure was compared with the known hexanuclear silver(I) complex {[Ag(μ-L1Clpz)]₃}₂. The Ag···Ag distances in [Ag(μ-L1Clpz)]_n are slightly shorter than twice Bondi’s van der Waals radius, indicating some Ag···Ag argentophilic interactions. Two Ag–N distances in [Ag(μ-L1Clpz)]_n were found: 2.0760(13) and 2.0716(13) Å, and their N–Ag–N bond angles of 180.00(7)° and 179.83(5)° indicate that each silver(I) ion is coordinated by two pyrazolyl nitrogen atoms with an almost linear coordination. Every five pyrazoles point in the same direction to form a 1-D zig-zag structure. Some spectroscopic properties of [Ag(μ-L1Clpz)]_n in the solid-state are different from those of {[Ag(μ-L1Clpz)]₃}₂ (especially in the absorption and emission spectra), presumably attributable to this zig-zag structure having longer but differently arranged intramolecular Ag···Ag interactions of 3.39171(17) Å. This result clearly demonstrates the different physicochemical properties in the solid-state between 1-D coordination polymer and metalacyclic trinuclear (hexanuclear) or tetranuclear silver(I) pyrazolate complexes. Full article

A new flexible bis-pyrazol-bis-acetate ligand, diethyl 2,2’-(pyridine-2,6-diylbis (5-methyl-1H-pyrazole-3,1-diyl))diacetate (L), has been synthesised, and three coordination complexes, namely, [Zn(L)₂](BF₄)₂ (1), [MnLCl₂] (2) and [CdLCl₂] (3) have been obtained. All ligands and complexes were characterised by IR, mass spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. Single crystal X-ray diffraction experiment revealed that the primary supramolecular building block of 1 is a hexagonal chair shaped 0D hydrogen bonded synthon (stabilised by C–H∙∙∙O hydrogen bonding and C=O∙∙∙π interactions), which further built into a 2D corrugated sheet-like architecture having a 3-c net honeycomb topology, and finally extended to a 3D hydrogen bonded network structure having a five nodal 1,3,3,3,7-c net, through C–H∙∙∙F interactions. On the other hand, the two crystallographically independent molecules of 2 exhibited two distinct supramolecular structures such as 2D hydrogen bonded sheet structure and 1D zigzag hydrogen bonded chain, sustained by C–H∙O and C–H∙∙∙Cl interactions, which are further self-assembled into a 3,4-c network structure, and 3 showed a 2D hydrogen bonded sheet structure. The supramolecular structural diversity in these complexes is due to the different conformations adopted by the ligands, which are mainly induced by different metal ions with coordination environments controlled by different anions. Hirshfeld surface analysis was explored for the qualitative and quantitative analysis of the supramolecular interactions. Full article

Two silver nitrate complexes with bisphosphines were obtained and characterized: [Ag(dcypm)]₂(NO₃)₂ (1; dcypm = bis(dicyclohexylphosphino)methane) and [Ag(dppm)]₂(Me₂Pz^H)_n(NO₃)₂ (n = 1, 2a; n = 2, 2b; dppm = bis(diphenylphosphino)methane, Me₂Pz^H = 3,5-dimethylpyrazole). The steric repulsions of bulky cyclohexyl substituents prevent additional ligand coordination to the silver atoms in 1. Compounds obtained feature the bimetallic eight-member cyclic core [AgPCP]₂. The intramolecular argenthophilic interaction (d(Ag···Ag) = 2.981 Å) was observed in complex 1. In contrast, the coordination of pyrazole led to the elongation of Ag···Ag distance to 3.218(1) Å in 2a and 3.520 Å in 2b. Complexes 1 and 2a possess phosphorescence both in the solution and solid state. Time-dependent density-functional theory (TD-DFT) calculations demonstrate the origin of their different emission profile. In the case of 1, upon excitation, the electron leaves the Ag–P bonding orbital and locates on the intramolecular Ag···Ag bond (metal-centered character). Complex 2a at room temperature exhibits a phosphorescence originating from the ³(M + L^P+N)L^PhCT state. At 77 K, the photoluminescence spectrum of complex 2a shows two bands of two different characters: ³(M + L^P+N)L^PhCT and ³LC^Ph transitions. The contribution of Ag atoms to the excited state in both complexes 2a and 2b decreased relative to 1 in agreement with the structural changes caused by pyrazole coordination. Full article

Octacyanometallate-based compounds displaying a rich pallet of interesting physical and chemical properties, are key materials in the field of molecular magnetism. The [M(CN)₈]ⁿ⁻ complexes, (M = W^V, Mo^V, Nb^IV), are universal building blocks as they lead to various spatial structures, depending on the surrounding ligands and the choice of the metal ion. One of the functionalities of the octacyanometallate-based coordination polymers or clusters is the magnetocaloric effect (MCE), consisting in a change of the material temperature upon the application of a magnetic field. In this review, we focus on different approaches to MCE investigation. We present examples of magnetic entropy change ΔS_m and adiabatic temperature change ΔT_ad, determined using calorimetric measurements supplemented with the algebraic extrapolation of the data down to 0 K. At the field change of 5T, the compound built of high spin clusters Ni₉[W(CN)₈]₆ showed a maximum value of −ΔS_m equal to 18.38 J·K⁻¹ mol⁻¹ at 4.3 K, while the corresponding maximum ΔT_ad = 4.6 K was attained at 2.2 K. These values revealed that this molecular material may be treated as a possible candidate for cryogenic magnetic cooling. Values obtained for ferrimagnetic polymers at temperatures close to their magnetic ordering temperatures, T_c, were lower, i.e., −ΔS_m = 6.83 J·K⁻¹ mol⁻¹ (ΔT_ad = 1.42 K) and −ΔS_m = 4.9 J·K⁻¹ mol⁻¹ (ΔT_ad = 2 K) for {[Mn^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_n and{[Fe^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_n, respectively. MCE results have been obtained also for other -[Nb(CN)₈]-based manganese polymers, showing significant T_c dependence on pressure or the remarkable magnetic sponge behaviour. Using the data obtained for compounds with different T_c, due to dissimilar ligands or other phase of the material, the ΔS_m ~ T_c^−2/3 relation stemming from the molecular field theory was confirmed. The characteristic index n in the ΔS_m ~ ΔHⁿ dependence, and the critical exponents, related to n, were determined, pointing to the 3D Heisenberg model as the most adequate for the description of these particular compounds. At last, results of the rotating magnetocaloric effect (RMCE), which is a new technique efficient in the case of layered magnetic systems, are presented. Data have been obtained and discussed for single crystals of two 2D molecular magnets: ferrimagnetic {Mn^II(R-mpm)₂]₂[Nb^IV(CN)₈]}∙4H₂O (mpm = α-methyl-2-pyridinemethanol) and a strongly anisotropic (tetren)Cu₄[W(CN)₈]₄ bilayered magnet showing the topological Berezinskii-Kosterlitz-Thouless transition. Full article