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Stoeckli-Evans, Helen

Nom
Stoeckli-Evans, Helen
Affiliation principale
Fonction
Professeur.e émérite
Email
helen.stoeckli-evans@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/470
_
0000-0002-9960-3869

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  • Publication
    Accès libre
    Dinuclear iron, ruthenium and cobalt complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo or hydroxo bridges
    (2006)
    Romakh, Vladimir B.
    ;
    Therrien, Bruno 
    ;
    Labat, Gael
    ;
    Stoeckli-Evans, Helen 
    ;
    Shul’pin, Georgiy B.
    ;
    Süss-Fink, Georg 
    The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L–Me2) with FeSO4 • 7H2O in aqueous ethanol gives, in the presence of sodium carboxylates, hydrogen peroxide, sodium hydroxide and KPF6, the dinuclear Fe(III)–Fe(III) complex cations [(L–Me2)2Fe2(O)(OOCR) 2]2+ (R = H: 1, R = CH3: 2, R = C6H5: 3), which crystallise as the hexafluorophosphate salts. The corresponding reaction with RuCl3 • nH2O does not work, however, the analogous Ru(III)–Ru(III) complex [(L–Me2)2Ru2 (O)(OOCCH3)2]2+ (5) can be synthesised by reacting Ru(dmso)4Cl2 with L–Me2, HCl and air in refluxing ethanol, followed by addition of sodium acetate, the mononuclear intermediate (L–Me2)RuCl3 • H2O (4) being also isolated and characterised. The reaction of L–Me2, sodium acetate, hydrogen peroxide and triethylamine with CoCl2 • 6H2O in acetonitrile yields, however, the hydroxo-bridged Co(III)–Co(III) complex [(L–Me2)2Co2 (OH)(OOCCH3)2]3+ (6). The molecular structures of 2, 5 and 6, solved by single-crystal X-ray structure analyses of the hexafluorophosphate salts, reveal for the orange crystals of [2][PF6]2 a Fe–Fe distance of 3.104(1) Å, for the purple crystals of [5][PF6]2 a Ru–Ru distance of 3.230(1) Å, and for the violet crystals of [6][PF6]3 • (CH3)2CO a Co–Co distance of 3.358(1) Å. All six complexes show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water to give acetone in the presence of ascorbic acid as co-catalyst.
  • Publication
    Accès libre
    Synthesis, structure and DNA interaction of cobalt(III) bis-complexes of 1,3-bis(2-pyridylimino)isoindoline and 1,4,7-triazacyclononane
    (2005)
    Tamil Selvi, Pitchumony
    ;
    Stoeckli-Evans, Helen 
    ;
    Palaniandavar, Mallayan
    The complex [CoL2](ClO4) • MeOH (1), where HL is the tridentate 3N ligand 1,3-bis(2-pyridylimino)isoindoline, has been isolated and its X-ray crystal structure successfully determined. It possesses a distorted octahedral structure in which both the ligands are coordinated meridionally to cobalt(III) via one deprotonated isoindoline (L−) and two pyridine nitrogen atoms. Interestingly, the average dihedral angle between pyridine and isoindoline rings is 25.9°, indicating that the ligand is twisted upon coordination to cobalt(III). The interaction of the complex with calf-thymus DNA has been studied using various spectral methods and viscosity and electrochemical measurements. For comparison, the DNA interaction of [Co(tacn)2]Cl3 (2), where tacn is facially coordinating 1,4,7-triazacyclononane, has been also studied. The ligand-based electronic spectral band of 1 and the N(σ) → Co(III) charge transfer band of 2 exhibit moderate hypochromism with small or no blue shift on interaction with DNA. The intrinsic binding constants calculated reveal that the monopositive complex ion [CoL2]+ exhibits a DNA-binding affinity lower than the tripositive complex ion [Co(tacn)2]3+. The steric clashes with DNA exterior caused by the second L− ligand bound to cobalt(III), apart from the lower overall positive charge on the [CoL2]+ complex, dictates its DNA-binding mode to be surface binding rather than partial intercalative interaction expected of the extended aromatic chromophore of deprotonated isoindoline anion. An enhancement in relative viscosity of CT DNA on binding to 1 is consistent with its DNA surface binding. On the other hand, a slight decrease in viscosity of CT DNA was observed on binding to 2 revealing that the smaller cation leads to bending (kinking) and hence shortening of DNA chain length. The electrochemical studies indicate that the DNA-bound complexes are stabilised in the higher Co(III) rather than the lower Co(II) oxidation state, suggesting the importance of electrostatic forces of DNA interaction.
  • Publication
    Accès libre
    Different complexation behavior of a proton transfer compound obtained from 1,10-phenanthroline and pyridine-2,6-dicarboxylic acid with InIII and CeIII: Synthesis, crystal structures and solution studies
    (2005)
    Ramezanipour, Farshid
    ;
    Aghabozorg, Hossein
    ;
    Shokrollahi, Ardeshir
    ;
    Shamsipur, Mojtaba
    ;
    Stoeckli-Evans, Helen 
    ;
    Soleimannejad, Janet
    ;
    Sheshmani, Shabnam
    The different complexation methods of a proton transfer compound LH2, (phenH)2 (pydc) (phen=1,10-phenanthroline; pydcH2=pyridine-2,6-dicarboxylic acid), are discussed and formation of [In2SO4 (pydc)2 (phen)2(H2O)2]•5.5H2O (1) and {[Ce(pydc)(pydcH)(H2O)2]•4H2O}n (2) are reported. The complexes were synthesized by reaction of LH2 with In2 (SO4)3•xH2O and Ce(NO3)3•6H2O, respectively. The characterization was performed using IR spectroscopy and X-ray diffraction. The complex 1 crystallizes in the space group РĪ of the triclinic system, with two molecules per unit cell. The unit cell parameters are a=11.9547(6) Å, b=12.8482(7) Å, c=16.1313(8) Å, α=89.532(1)°, β=72.007(1)° and γ=68.066(1)°. The crystal system of the complex 2 is monoclinic with space group P21lc and four molecules per unit cell. The unit cell parameters are a=14.0273(8) Å, b=11.2184(6) Å, c=12.9441(8) Å and β=102.177(5)°. The complex 1 is a binuclear mixed-ligand system in which both phen and (pydc)2− have contributed to the molecular structure as tri- and bi-dentate ligands, respectively. The complex 2 is a polymeric system in which only one of the fragments of LH2 has acted as a ligand. In both complexes 1 and 2 a large number of hydrogen bonds are observed. These interactions especially in case of complex 2 play an important role in the formation of self associated systems in the crystal lattices. Results of the potentiometric pH titration studies in aqueous solution strongly confirm the formation of InIII and CeIII complexes in solution with stoichiometries very similar to those of the crystalline complexes 1 and 2, respectively.