Formation Of Mononuclear Complexes Research Articles

Double-Armed 18- and 21-Membered Macrocycles as Potential Chelators for Lead and Bismuth Radiopharmaceuticals.

With increasing clinical applications and interest in targeted alpha therapy, there is growing interest in developing alternative chelating agents for [212Pb]Pb2+ and [212/213Bi]Bi3+ that exhibit rapid radiolabeling kinetics and kinetic inertness. Herein we report the synthesis and detailed investigation of diacetate and dipicolinate 18- and 21-membered macrocyclic chelators BADA-18, BADA-21, BADPA-18, and BADPA-21 for the complexation of Pb2+ and Bi3+ ions with potential use in the preparation of radiopharmaceuticals. The formation of mononuclear complexes was established by using ESI-mass spectrometry, and their stability constants were determined by potentiometric titration. A thorough study of the structure of the metal complexes was carried out by using X-ray diffraction and NMR spectroscopy. It was shown how the stability of the complex is influenced by an increase in the size of the macrocycle, the replacement of acetate arms with picolinate ones, the rigidity of the ligand, as well as the type of conformation (syn- or anti-) of the metal complex. The new ligands were radiolabeled with [210Pb]Pb2+ and [207Bi]Bi3+, and the in vitro stability of the resulting complexes in a competitive environment of serum and biologically significant metal ions was assessed. Rapid complex formation in 1-2 min at room temperature, as well as the high kinetic inertness of the complexes Pb(BADPA-18) and Bi(BADPA-18) in biological media, demonstrate its potential for use in targeted radionuclide therapy.

Role of non-redox innocent ligand units in the oxidation of alcohols with H2O2 catalyzed by μ-oxido-diiron(III) bis-phenolato polypyridyl complexes

Redox non-innocent ligands hold the potential to expand the redox chemistry and activity of transition metal catalysts. The impact of the additional redox chemistry of phenol ligands in oxidation catalysis is explored here in the complex μ-oxido-diiron(III) polypyridyl (1) [(L)Fe(III)(μ–O)Fe(III)(L)](ClO4)2 (where HL is 2-(((di(pyridin-2-yl)methyl) (pyridin-2-ylmethyl) amino)methyl)phenol) and its tert-butyl substituted analog 2, in which each of the Fe(III) centers is coordinated to a phenolato moiety of the ligand. Complex 1 was shown earlier to catalyse the oxidation of benzyl alcohols to aldehydes with H2O2. In particular acid was found to accelerate the reactions by removal of a lag period before catalysis initiated. Here, we use reaction monitoring with resonance Raman, UV/vis absorption and EPR spectroscopy to show that under catalytic conditions, i.e. with excess H2O2, rapid (< 5 s) loss of the phenolato moiety occurs, resulting in the formation of an N4 ligated Fe(III) complex. This N4 coordinated complex forms a Fe(III)-OOH species, which is responsible for alcohol oxidation and over time a relatively stable oxido-bridged dinuclear Fe(III) complex forms as a resting state in the catalytic system. The main role of acid in the catalysis is shown to be to facilitate the initial coordination of H2O2 by driving the formation of mononuclear complexes from 1 and 2. The data show that although the phenolato moiety imparts interesting redox properties on complex 1, it does not contribute directly to the oxidation catalysis observed with H2O2.

New copper(II) cyclam complexes with aminocarboxylate co-ligands: Synthesis, characterization, and in vitro antiproliferative and antibacterial studies

Two new cationic Cu(II) complexes of cyclam (1,4,8,11-tetraazacyclotetradecane) and aminocarboxylate coligands glycine or alanine have been synthesized. The complexes were characterized by elemental analysis (C, H and N), molar electrical conductivity, magnetic susceptibility measurement at room temperature, spectral methods (UV/Vis and Fourier transform infrared), as well as by thermogravimetric (TG) and differential thermal analysis (DTA). The analytical data of the complexes show the formation of mononuclear complexes with general formula [Cu(L)cyc](ClO4)2?nH2O, A) L = glycine, n = 1.5 and B) L = alanine, n = 2.5. The tetradentate ligand cyclam was coordinated to metals through four N donors. The spectroscopic data suggested that the amino carboxylate ligands coordinated via their carboxylate ion moieties. The six- -coordinate octahedral geometry around Cu(II) in both complexes was presumed. TG-DTA analysis indicated that complex B decomposed exothermally in a single step in the range of 310?400?C. The cytotoxic activity of Cu(II) complexes and the starting ligands were tested against human cervix adenocarcinoma cell line (HeLa), human melanoma (FemX) and human colon carcinoma (LS174). The IC50 values for the Cu(II) complexes were from 48.35?82.25 ?M. Both complexes were tested for their antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli and the yeast Candida albicans.

A novel manganese(II) bisthiocarbohydrazone complex: Crystal structures, Hirshfeld surface analysis, DFT and molecular docking study with SARS-CoV-2

A novel Mn(II) complex [Mn(H2L)Cl2]•H2O (1) of a ditopic ligand 1,5-bis(2-benzoylpyridine) thiocarbohydrazone (H2L) was synthesized and characterised physico-chemically. A part of the mother solution of the complex 1 and THF yielded single crystals in a triclinic space group and are found same from the crystals obtained from another mixture of the mother solution and ethyl acetate. Single crystal XRD studies have confirmed the mononuclear complex formation and absence of any interactions between the Mn(II) centers. A solution of the complex 1 in chloroform, conversely, yielded a crystallographically different complex [Mn(H2L)Cl2]•CHCl3 (1a) in monoclinic and is also characterised with single crystal XRD. The ligand is coordinated through thione sulfur atom to form a square pyramidal geometry around Mn(II) center in both the complexes. The molecular packing of the complexes is found influenced by the nature of solvent inclusion, and are stabilized by different non-covalent interactions in the lattice. The intermolecular interactions are quantified by Hirshfeld surface analyses, which reveal that H•••Cl interactions has maximum contribution to the total Hirshfeld surface in the complex 1a. This is the first crystal structure study of a manganese(II) complex of a bisthiocarbohydrazone ligand. The molecular and electronic structures of the complexes are studied by DFT quantum chemical calculations. The band gap (Eg) of the complex 1 was estimated as 2.45 eV using Kubelka-Munk model and is in agreement with the electronic spectral calculations of the complex at TD-DFT level. Molecular docking studies of both the ligand and the complex reveal their greater propensity towards SARS-CoV-2 main protease compared to B-DNA dodecamer. Also, the binding potential of the ligand and the complex with SARS-CoV-2 main protease is found higher than that with chloroquine and hydroxychloroquine.

Heteroleptic Samarium(III) Chalcogenide Complexes: Opportunities for Giant Exchange Coupling in Bridging σ- and π-Radical Lanthanide Dichalcogenides.

The introduction of (N2)3–• radicals into multinuclear lanthanide molecular magnets raised hysteresis temperatures by stimulating strong exchange coupling between spin centers. Radical ligands with larger donor atoms could promote more efficient magnetic coupling between lanthanides to provide superior magnetic properties. Here, we show that heavy chalcogens (S, Se, Te) are primed to fulfill these criteria. The moderately reducing Sm(II) complex, [Sm(N††)2], where N†† is the bulky bis(triisopropylsilyl)amide ligand, can be oxidized (i) by diphenyldichalcogenides E2Ph2 (E = S, Se, Te) to form the mononuclear series [Sm(N††)2(EPh)] (E = S, 1-S; Se, 1-Se, Te, 1-Te); (ii) S8 or Se8 to give dinuclear [{Sm(N††)2}2(μ-η2:η2-E2)] (E = S, 2-S2; Se, 2-Se2); or (iii) with Te=PEt3 to yield [{Sm(N††)2}(μ-Te)] (3). These complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, FTIR, and electronic spectroscopy; the steric bulk of N†† dictates the formation of mononuclear complexes with chalcogenate ligands and dinuclear species with the chalcogenides. The Lα1 fluorescence-detected X-ray absorption spectra at the Sm L3-edge yielded resolved pre-edge and white-line peaks for 1-S and 2-E2, which served to calibrate our computational protocol in the successful reproduction of the spectral features. This method was employed to elucidate the ground state electronic structures for proposed oxidized and reduced variants of 2-E2. Reactivity is ligand-based, forming species with bridging superchalcogenide (E2)−• and subchalcogenide (E2)3–• radical ligands. The extraordinarily large exchange couplings provided by these dichalcogenide radicals reveal their suitability as potential successors to the benchmark (N2)3–• complexes in molecular magnets.

In situ formation of mononuclear complexes by reaction-induced atomic dispersion of supported noble metal nanoparticles

Supported noble metal nanoclusters and single-metal-site catalysts are inclined to aggregate into particles, driven by the high surface-to-volume ratio. Herein, we report a general method to atomically disperse noble metal nanoparticles. The activated carbon supported nanoparticles of Ru, Rh, Pd, Ag, Ir and Pt metals with loading up to 5 wt. % are completely dispersed by reacting with CH3I and CO mixture. The dispersive process of the Rh nanoparticle is investigated in depth as an example. The in-situ detected I• radicals and CO molecules are identified to promote the breakage of Rh-Rh bonds and the formation of mononuclear complexes. The isolated Rh mononuclear complexes are immobilized by the oxygen-containing functional groups based on the effective atomic number rule. The method also provides a general strategy for the development of single-metal-site catalysts for other applications.

Metal complexes based on substituted aliphatic acid derived from a Diels-Alder adduct: Synthesis and potential ratiometric luminescent temperature sensor of d10 complex

A condensation reaction between the Diels-Alder adducts of anthracene and maleic anhydride with β-alanine leads to the formation of a new compound, HL. A one-pot reaction of HL with Cu(OAc)2·H2O afforded the formation of mononuclear complex, [CuL2(H2O)3] (1). By leaving the blue crystal of 1 in high concentrated methanolic vapor resulting the formation of pale green crystal of dinuclear complex, [Cu2(µ-L)4(MeOH)(H2O)] (2). This observation indicated the solvent-vapor mediated single-crystal-to-single-crystal (SCSC) transformation that promoted nuclearity cross-over from mononuclear to dinuclear of Cu(II) complex. This phenomenon is due to the removal/exchange of water/solvent molecules and subsequent structural rearrangement in the crystalline phase. The reactions of HL with Ni(OAc)2·H2O and Ag(OAc)·H2O afforded the formation of 1-D coordination polymer, [NiL2(µ-H2O)2(H2O)2]n·nH2O (3) and dinuclear complex [Ag2(µ-L)2(H2O)2] (4), respectively. Photoluminescence analysis on complex 4 reveals that this dinuclear has potential as a ratiometric luminescent temperature sensor.

Structural elucidation of N^O (ethylimino-methyl)phenol Fe(II) and Co(II) complexes and their applications in ethylene oligomerization catalysis

Reactions of 2-[(2-hydroxyethyl)imino]methyl]phenol (L1H), 2-[1-[(2-hydroxyethyl)imino]ethyl]phenol (L2H) and 2-[{[(2-diethylamino)ethyl]imino}methyl]phenol (L3H) with CoCl2 and FeCl2 salts produced the metal complexes [Co(L1)2] (Co1), [Fe(L1)2] (Fe1), [Co(L2)2] (Co2), [Fe(L)2] (Fe2), [Co2(L3H)2Cl4)] (Co3) and [Fe2(L3H)2Cl4] (Fe3), respectively. Molecular structureof Fe1 confirmed the formation of mononuclear complex containing two tridentate bound anionic ligand L1. On the other hand, the solid state structure of Co3 established the formation of a dinuclear complex bearing a bidentate zwitterionic ligand L3H. Activation of the Fe(II) and Co(II) complexes with EtAlCl2 or MAO co-catalysts, gave active catalysts in oligomerization of ethylene to give C4 and C6 oligomers. Generally, the Co(II) complexes exhibited higher catalytic activities than their Fe(II) analogues. While activation with MAO produced mainly C4 oligomers (96%), EtAlCl2 gave predominantly C6 oligomers. Density functional theory data provided insights on the catalytic activity trends and effect of complex/ligand structure on the ethylene oligomerization reactions.

Complex formation between copper(II) and arginine in two ionic media and in a large range of reagent concentration

Arginine and copper(II) play an important role in human physiology. Arginine is a precursor of NO which is a vasodilator and the right quantity of copper(II), bound to several amino acids, is necessary for the human body. The complex formation between copper(II) and arginine is studied at 25 °C and in two different ionic media: 1.00 mol dm−3 NaClO4 and 1.00 mol dm−3 NaCl. The investigation is carried out potentiometrically, by employing in 1.00 mol dm−3 NaClO4 cells involving glass and copper amalgam electrodes. In 1.00 mol dm−3 NaCl, only the glass electrode can be used. In both ionic media, the adoption of the constant ionic medium allows to extend the investigation to a large range of reagent concentration. Experimental data can be explained by assuming the formation of mononuclear complexes in copper(II). In 1.00 mol dm−3 NaClO4, complexes with the participation of hydrogen ions are assumed. The presence of the main complex in a large hydrogen ion concentration is supported also by spectrophotometric measurements.

Experimental and theoretical studies on structure, bonding and luminescence properties of Eu(III) and Tb(III) complexes of a new macrocyclic based 8HQ ligand

8-Hydroxyquinolate complexes of lanthanide have a variety of applications in electroluminescent devices due to their unique luminescence properties. But, the simple 8HQ ligand has a tendency to form polynuclear complexes. However, linking several 8HQ units to a single moiety facilitates the formation of mononuclear complexes due to flexibility, preorganization, π-stacking and entropy effect. Mononuclear complexes of europium and terbium ions with a new chelator, [1,4,7-tris-{(5-methylene-8-hydroxyquinoline)-1,4,7-triazacyclononane}], embedded with these prerequisites are synthesized and characterized. Each Ln(III) is nine-coordinate and bonded to three sets of O,N-donors of 8HQ units and three water resulting in a pseudo-C3 symmetric tricapped trigonal prismatic geometry. In silico studies suggest that the metal ion can easily be encapsulated in the central cavity of the ligand without changing its basic structure. Interesting, diverse behavior was observed for photoluminescence spectral studies in solid and solution state. At room temperature, an antenna effect was observed for the complexes only in the powder form. The experimental photoluminescence studies have been explained with the help of TDDFT. The nature of bonding between the lanthanide and the ligand, interpreted by NBO and ETS-NOCV, suggest that the Ln-L bonds are ∼25% covalent. The Slater Condon parameters, spin-orbital coupling constants, and the nephelauxetic parameters were calculated from LF-DFT.

Piperazine core-containing Schiff ligands define chemical reactivity toward divalent metal ions

A series of homologous Schiff bases N,N′-bis[(4-decyloxy-salicylideneamino)-n-propyl]-piperazine] (ZOPPH2), and N,N′-bis[(4-dodecyloxy-benzylideneamino)-n-propyl]-piperazine (DBPP)(1), based on 1,4-bis(3-amino-propyl)-piperazine (APPZ), were designed and synthesized, with APPZ serving as the piperazine core, bilaterally flanked by extended alkyl chain-containing antennae. Driven by the pursuit of metallomesogenic materials bearing liquid crystalline state properties, chemical reactivity toward divalent metals Co(II) and Cu(II), in alcoholic or tetrahydrofuran/dimethylsulfoxide media, led to compounds [{Co(ZOPP)}(ClO4)]2.(CH3OH).2(CH3)2SO(2) and [Cu(APPZ)Cl]Cl(3). All materials were characterized by elemental analysis, spectroscopic techniques (UV–Visible, FT-IR, NMR where appropriate), molar conductivity, and X-ray crystallography. Physicochemical characterization emphasizes the a) importance of N,O-containing Schiff anchors in metal ion binding, b) significance of the phenolic moiety, on the flanks of the Schiff ligands, in promoting either metal ion complexation or dissociation of the Schiff base at the azomethine moiety junction, thereby altering metal ion chemical reactivity, and c) observed oxidation of Co(II) to Co(III) upon mononuclear complex formation. Hybrid DFT calculations on DBPP and ZOPPH2 suggest increased reactivity of the Schiff CHN moiety, in the absence of the phenolic moiety, and concurrent metal ion presence, thereby lending credence to the notion of metal-assisted rupture of the specific bond in DBPP and the emergence of specific metal-ligand product(s). Collectively, the data denote the significance of structural features of piperazine-core Schiff antennae ligands in a) promoting chemical reactivity toward transition metals, b) defining metal-ligand complexation and lattice architecture, and c) parameterizing such chemical reactivity into synthetic advances toward new materials with well-defined solid-state architecture, lattice and physicochemical properties.

Complexes in aqueous cobalt(II)–2-picolinehydroxamic acid system: Formation equilibria, DNA-binding ability, antimicrobial and cytotoxic properties

The coordination properties of 2-picolinehydroxamic acid towards cobalt(II) in aqueous solution were determined by a pH-metric method and confirmed by spectroscopic (UV–Vis and ESI-MS) studies. The results show the formation of mononuclear complexes, as well as of metallacrowns (MC). All methods indicate a high tendency of 2-picolinehydroxamic acid to form cobalt(II) metallacrown 12-MC-4. ESI-MS additionally confirms 15-MC-5 and 18-MC-6, stabilized by a sodium ion and methanol. The complexes observed in the speciation model at a pH about 7.2 were studied for their DNA-binding ability. The decrease of absorbance in the range of ca 310–400 nm indicates effective binding to calf thymus DNA by 2-picolinehydroxamic acid complexes, via intercalative mode. The antimicrobial properties of 2-picolinehydroxamic acid, cobalt(II) ions and of the complexes formed in the Co(II) – ligand system were determined against Gram-positive bacteria (Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, Bacillus subtilis), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori) and fungal strains (Candida, Aspergillus niger). The results indicate that the complexes demonstrate greater antibacterial and antifungal activity for most strains than the ligand. Both the complexes and the ligand induce a slight decrease in the metabolic activity of cells, while the complexes do not damage the cell nuclei. The 2-picolinehydroxamic acid complexes activate the human monocytic cells, suggesting they have immunomodulating properties, which are particularly important in combating infections caused by strains resistant to other drugs.

Electronic effects on the structures and catalytic properties of (pyrazol-1-yl)phenylmethanone palladium(II) complexes

Four new (pyrazol-1-yl)phenylmethanone ligands and their palladium(II) complexes were synthesized and characterized by various analytical techniques. The electronic properties of substituents on the phenyl ring of the ligand have significant effects on the structures as well as the catalytic properties of the complexes toward ethylene oligomerization and the subsequent Friedel-Crafts alkylation of toluene by the ethylene oligomers. Electron-withdrawing groups (ca. Cl and F) of the ligands contributed to the formation of binuclear palladium complexes, whereas electron-donating groups (ca. H and CH3) resulted in the formation of mononuclear complexes. These complexes on activation with EtAlCl2 form active catalysts which dimerize ethylene to mainly butenes (C4) and subsequent Friedel-Crafts alkylation of toluene by butenes to regioisomers of butyltoluenes. This is the first example of pyrazolyl palladium(II) compounds that perform this tandem reaction of oligomerization and Friedel-Crafts alkylation.

Pyridyl azine Schiff-base ligands exhibiting unexpected bonding modes towards ruthenium, rhodium and iridium half-sandwich complexes: Synthesis and structural studies

The reaction of multidentate azine Schiff-base ligands was investigated towards p-cymene ruthenium, Cp*Rh and Cp*Ir complexes. The reaction of [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) with azine Schiff-base ligands (L1-L3) in 1:2 M ratio led to the formation of mononuclear complexes of the type [(arene)M(L)Cl]+ whereas the reaction of [Cp*MCl2]2 (M = Rh/Ir) with azine Schiff-base ligands (L1-L3) in 1:1 M ratio afforded dinuclear rhodium and iridium complexes bearing formula [{Cp*MCl}2(μ-L)]+ (M = Rh/Ir). The ligands in dinuclear complexes exhibited interesting coordination modes towards the metal atom. The reaction of ligand L3 with [Cp*IrCl2]2 dimer yielded two coordination isomers whereas with [Cp*RhCl2]2 yielded exclusively one isomer. The molecular structure of both the isomers of the iridium complex has been established. In rhodium and iridium complexes the ligand L3 acted as uninegative pentadentate bridging ligand coordinating one metal center in a tridentate fashion and the other metal in a bidentate fashion. In the other isomer the ligand L3 behaved as uninegative tetradentate bridging ligand coordinating both iridium centers in a bidentate fashion. In the mononuclear complexes, the ligands are coordinated to the metal atom in a bidentate N∩N fashion through pyridine nitrogen and azine nitrogen. The ligand (L1 and L2) acted as tetradentate bridging ligand in dinuclear complexes. All these complexes were isolated and characterized by spectroscopic and analytical techniques.

Synthesis, Structural and Biological Studies of Some Half‐Sandwich d6‐Metal Complexes with Pyrimidine‐Based Ligands

AbstractThe reaction of metal precursors {[Cp*MCl2]2 (M=Rh, Ir)} with 2‐aminopyrimidine (L1) gave binuclear complexes as [(Cp*MCl2)2(μ‐L1)], where L1 acted as a bridging ligand. While 2‐mercaptopyrimidine (L2) with [Cp*MCl2]2 {M=Rh(III), Ir(III)} formed mononuclear di substituted complexes as [Cp*M(L2)2], where L2 acted as a chelating as well as a monodentate ligand. The reaction of [CpRu(PPh3)2Cl] with 2‐mercaptopyrimidine (L2) led to the formation of mononuclear complex as general formula [CpRu(PPh3)(L2)] in presence of a base. 2‐Mercaptopyrimidine ligand resulted complexes with strained four‐membered metallacycle while 2‐aminopyrimidine yielded bridged complexes. HOMO‐LUMO energy gaps and UV‐Visible bands were additionally rationalised by the DFT studies. The binding ability of the complexes to the CT‐DNA was confirmed using UV‐Visible and fluorescence spectroscopy. In vitro antibacterial activity of the complexes was evaluated against human pathogenic bacteria. Cytotoxicity of the complexes was examined by the MTT assay over three cancerous and one non‐cancer cell lines viz., BE, HT‐29, MIA−Pa‐Ca2 and ARPE‐19.

Cystine as Ligand of Calcium(II) and Magnesium(II) in Two Ionic Media and at Two Different Temperatures (25 and 37 °C)

Cystine plays an important role in human physiology, it is the precursor of cysteine. Cystine is the molecular form preferred by the immunity cellules system, included macrophages. Although slightly soluble, it can be a ligand towards cations because it is a sulfur-containing amino acid. Because of the physiological importance of calcium(II) and magnesium(II), complex formation between these cations and cystine was studied potentiometrically by employing electrochemical cells involving glass electrodes. The investigation was performed at two temperatures (25 and 37) °C and in two ionic media (1.00 and 0.15 mol·dm−3 NaCl). In both ionic media, the adoption of a constant ionic medium allows extension of the investigation to a large range of reagent concentration. As the formation of weak complexes was foreseen, the low solubility of cystine is an advantage. Experimental data can be explained in any case by assuming the formation of mononuclear complexes in the presence of both calcium(II) and magnesium(II). The relative stability constants were determined.

The spectroscopic studies of new polymeric complexes of silver(I) and original mononuclear complexes of lanthanides(III) with benzimidazole-based hydrazone

Three new complexes of silver(I) (1–3) with (E)-2-(1-methyl-2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)-1H-benzoimidazole L were synthesized and the influence of counterions on crystal packing was investigated. Complexation reactions of L with lanthanides lead to formation of mononuclear complexes [Eu(L)3](CF3SO3)3 (4), [Gd(L)(NO3)3(CH3CN)] (5) and [Tb(L)(NO3)3(CH3CN)] (6). The ligand and complexes were characterized by elemental analysis, FT-IR and UV–Vis spectroscopy. The crystal structures of ligand and its silver(I) complexes were determined by single-crystal X-ray diffraction analysis. The luminescent properties of ligand L and complexes have been studied in solution and solid state.

Thiacalix[4]arene Derivatives Bearing Imidazole Units: A Ditopic Hard/Soft Receptor for Na+ and K+/Ag+ with an Allosteric Effect and a Reusable Extractant for Dichromate Anions

AbstractTwo novel receptors 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis[(ethoxycarbonyl)methoxy]‐26,28‐bis‐[1‐methyl‐(imidazole)meth‐oxy]‐2,8,14,20‐tetra‐thiacalix[4]arene (L1) and 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis‐[(benzyl)methoxy]‐26,28‐bis‐[1‐methyl‐(imidazole)‐methoxy]‐2,8,14,20‐tetrathiacalix[4]arene (L2) possessing imidazole moieties based on thiacalix[4]arene in the 1,3‐alternate conformation have been synthesized and characterized. The crystal structures of L1 and L2 have been determined. The binding behaviour towards Li+, Na+, K+ and Ag+ ions has been examined by 1H NMR titration experiments in (CDCl3/CD3CN; 10:1, v/v) solution. The exclusive formation of mononuclear complexes of L1 with metal cations is of particular interest revealing a negative allosteric effect in the thiacalix[4]arene family. Liquid‐liquid extraction experiments indicate that synthesized L2 can be utilized as an efficient reusable extractant for dichromate anion by controlling the pH of the aqueous solution.

Syntheses, structures and biological activities of square planar Ni(II), Cu(II) complexes

Ni(II) and Cu(II) complexes of a tridentate Schiff base ligand, N-(2-hydroxyphenyl)-3-methoxy-salicylideneamine (H2L) have been synthesized and characterized by IR, NMR, UV–Vis spectroscopy and elemental analysis. The solid state structures of complexes have been determined by single crystal X-ray diffraction analyses. The molecular structures shows the formation of mononuclear complexes [(NiL(1Me-Im)] (1), [(CuL(1Me-Im)] (2) and [(NiL(PPh3)] (3) (1Me-Im=1-methylimidazole and PPh3=triphenylphosphine). The Ni(II) or Cu(II) ion is situated in a square planar environment and coordinated by the NO2 donors of the Schiff base ligand and 1Me-Im (1–2) or PPh3 (3). The interactions of complexes 1–3 with DNA have been investigated by EtBr displacement experiments and spectroscopic titrations. The MTT assay showed no significant toxicity of 1, 3 and increasing toxicity of 2 at lower concentration.

Synthesis and structural studies of arene ruthenium and Cp*Rh/Cp*Ir complexes containing pyridylpyrazole- and pyridylthiazole-based ligands

The reactions of [(arene)RuCl2]2 (arene = p-cymene or benzene) and [Cp*MCl2]2 (M = Rh or Ir) with N,N′-bidentate chelating ligands 2-[3-(2-pyridyl)pyrazolyl]pyrimidine (L1) and 4-phenyl-(2-pyridyl)thiazole (L2) leads to the formation of mononuclear complexes of general formula [(arene)/Cp*M(L)Cl]PF6. Eight such complexes have been prepared and characterized by spectroscopic techniques. In addition, five of the complexes were also characterized by single-crystal X-ray diffraction. These complexes have typical piano-stool geometries around the metal center, with five-membered metellacycles in which L1 and L2 both act as N,N′-chelating ligands. Moreover, L1 prefers to coordinate through its pyrimidine and pyrazolyl nitrogen atoms, rather than the pyridine nitrogen.