Showing papers by "Wolfgang Linert published in 2014"

Versatile coordination modes of bis[5-(2-pyridine-2-yl)-1,2,4-triazole-3-yl]alkanes in Cu(II) complexes

Abstract: Nine new mononuclear and polynuclear Cu(II) complexes [Cu(H2L2)Cl]Cl·3H2O (1), [Cu(H2L3)Cl]Cl·H2O (2), [Cu(H2L4)Cl]Cl·2.5H2O (3), [Cu3(μ3-L1)2(H2O)3](ClO4)2·H2O (4), [Cu4(μ-HL1)4](ClO4)8·CH3OH·5H2O (5), [Cu2(HL3)2](ClO4)2·2H2O (6a), [Cu2(μ-HL3)2](ClO4)2·H2O (6b), [Cu2(μ-HL3)(L3)Cu(teta)](ClO4)3·2H2O (7) and [Cu2(H2L3)2(ox)](ClO4)2·2H2O·2MeOH (8) containing [5-(2-pyridine-2-yl)-1,2,4-triazole-3-yl]alkanes (H2Ln, n = 1–4) in combination with other ligands, such as chlorido, aqua, triethylenetetramine (teta) and/or oxalato (ox2−), were synthesized and characterized by various techniques such as elemental analysis, FTIR, NMR and UV-Vis spectroscopy. X-ray structures of H2L3 and H2L4 as well as complexes 1–8 were determined. The X-ray structures revealed that relatively small composition and structural changes in the H2Ln ligands have a substantial impact on the coordination geometries of the complexes themselves as well as on their resulting magnetic properties. It has been found that the geometries of the complexes vary from square-pyramidal to trigonal-bipyramidal (with τ ranging from 0.00 to 0.96) and, moreover, that the trigonal bipyramidal geometry becomes more preferable with the increase in the length of the polymethylene chain within the corresponding H2Ln ligand. The magnetic properties of the polynuclear compounds 4, 5, 6, 7 and 8 were analysed using the spin Hamiltonian formalism, which revealed the presence of antiferromagnetic exchange in the polynuclear systems mediated by the title ligands. The significant effect of the geometric parameters on the Cu⋯Cu exchange interactions in the polynuclear complexes is discussed.

Polymorphism dependent light induced spin transition

Abstract: A photomagnetic study of orthorhombic and tetragonal low spin polymorphs of compound [Fe(L)2](BF4)2 revealed different properties and thermal stability of their metastable high spin states. Furthermore, the reversible thermally induced phase/spin transition between low spin and high spin orthorhombic phases was studied by variable temperature UV/VIS spectroscopy.

Ligand substitution reaction on a platinum(II) complex with bio-relevant thiols: kinetics, mechanism and bioactivity in aqueous medium

Abstract: The kinetics of the interaction between [Pt(pic)(H2O)2](ClO4)2, cis-diaqua(2-aminomethylpyridine)platinum(II) perchlorate 1 and selected thiols (L-cysteine and N-acetyl-L-cysteine) has been studied spectrophotometrically in aqueous medium as a function of complex and thiol concentrations, pH, and temperature at constant ionic strength. The observed pseudo-first-order rate constants kobs (s−1) obeyed the equation kobs = k1[thiol]. At pH = 4.0, complex 1 interacts with the thiols via two distinct consecutive steps. The first step is dependent while the second step is independent of ligand concentration. The rate constants for the process are of the order: k1 ≈ 10−3 M−1 s−1 and k2 ≈ 10−5 s−1. The association equilibrium constant (KE) for the outer sphere complex formation has been evaluated together with the rate constants for the two subsequent steps. Both the steps are ligand-assisted anation and the final step is the ring closure process. The activation parameters for both steps were evaluated using Eyring's equation. The low ΔH‡1 = (34.91 ± 0.97 kJ mol−1) and ΔH‡2 = (29.10 ± 0.72 kJ mol−1) values and large negative values of ΔS‡1 = (−174.68 ± 2.18 J K−1 mol−1) and ΔS‡2 = (−233.74 ± 2.4 J K−1 mol−1) for both the anation steps were evaluated. On the basis of the kinetic observations, evaluated activation parameters and spectroscopic data, a plausible associative mechanism is proposed for both processes. Antibacterial properties on both gram positive and gram negative bacteria and anticancer properties of complex 1 and its substituted complexes 2 and 3 on HeLa cells have been investigated. Complexes 1 to 3 show remarkable growth inhibition of bacteria. They also show anticancer activity of about 70% when compared to cis-platin. The complexes bind to DNA and change its electrophoretic mobilization pattern in agarose gel.

Catalytic role of ruthenium(III) complexes bearing cystamine-based disulfide ligands on the N-alkylation of o -substituted anilines

Abstract: Ruthenium(III) complexes of cystamine-based disulfide ligands with the general formula [RuXL1−4] (X = Cl or Br; L1−4 = pentadentate Schiff base ligands) were synthesized from ruthenium precursor complexes [RuX3(AsPh3)3] (X = Cl or Br) and disulfide ligands derived from cystamine and 2-hydroxy-substituted aromatic aldehydes, viz., salicylaldehyde, 5-chlorosalicylaldehyde, o-vanillin, and 2-hydroxynaphthaldehyde for L1–L4, respectively. The ligands and their complexes were structurally characterized by elemental, spectral (UV–Vis, IR, NMR, EPR, and ESI-mass) and cyclic voltammetry methods. The new complexes have shown effective hydrogen transfer properties, which were studied in the catalytic transfer hydrogenation of some secondary alcohols using gas chromatography. The catalytic properties of the complexes toward the N-alkylation of o-substituted anilines were analyzed in detail showing that this catalytic reaction involved two important hydrogen transfer steps. Hence, a new suitable and efficient catalytic system has been investigated for the synthesis of various benzazoles in a one-pot reaction.

Kinetics and mechanism of biphasic substitution reactions of a platinum(II) complex with thioglycollic acid and 4-methyl-3-thiosemicarbazide in aqueous solution

Abstract: The kinetics of interactions between cis-diaqua(2-aminomethylpyridine)platinum(II) perchlorate (1) [Pt(pic)(OH2)2](ClO4)2, thioglycollic acid (TGA), and 4-methyl-3-thiosemicarbazide (MTSC) have been studied spectrophotometrically in aqueous medium as a function of the [complex (1)] as well as [TGA] or [MTSC], pH and temperature at constant ionic strength. The observed pseudo-first-order rate constants were proportional to [TGA] or [MTSC]. At pH 4.0, the interactions of (1) with both TGA and MTSC show two distinct consecutive steps; the first step is dependent and second independent of [TGA] or [MTSC]. The association equilibrium constant (K E) for the outer sphere complex formation has been evaluated, along with the rate constants for the two steps. The first step is assigned to ligand-assisted anation and the second to chelation of TGA or MTSC. The activation parameters for both the steps were evaluated using Eyring’s equation. On the basis of the kinetic observations and evaluated activation parameters, an associative mechanism is proposed for both the reactions.

Adducts of lanthanide acetylacetonates with 5-phenyl-2-(2-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine: structure and photoluminescence

Abstract: A series of isostructural complexes of the formula Ln(acac)3L (where Hacac is the acetylacetone, L is the 5-phenyl-2-(2-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine, Ln are the LaIII, TbIII, EuIII, and SmIII) was studied. Molecular and crystal structures of terbium and samarium complexes were established by X-ray diffraction analysis. Luminescence properties of solid samples were studied. Coordination of 5-phenyl-2-(2-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine as an additional ligand increases intensity of photoluminescence. Luminescence spectra of compositions Eu x Tb1−x (acac)3L and La0.6Eu0.1Tb0.3(acac)3L were studied. A combination of several lanthanide ions allowed us to obtain almost white emission.

The Hamiltonian of the molecular statistical model of spin crossover

Abstract: We derived an Ising-like Hamiltonian corresponding to the mathematical solutions of the free energy functional, taking into account binary and ternary interactions Parameters of this Hamiltonian refer to the properties of binary and many-body molecular interactions, whereas those of the original Ising-like Hamiltonian refer to the properties of sublattices