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Stoeckli-Evans, Helen

Nom
Stoeckli-Evans, Helen
Affiliation principale
Email
helen.stoeckli-evans@unine.ch
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https://libra.unine.ch/handle/123456789/470

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  • Publication
    Accès libre
    Three-dimensional bimetallic octacyanidometalates [MIV{(μ-CN)4MnII (H2O)2}2•4H2O]n (M = Nb, Mo, W): Synthesis, single-crystal X-ray diffraction and magnetism
    (2008)
    Herrera, Juan Manuel
    ;
    Franz, Patrick
    ;
    Podgajny, Robert
    ;
    Pilkington, Melanie
    ;
    Biner, Margret
    ;
    Decurtins, Silvio
    ;
    Stoeckli-Evans, Helen 
    ;
    Neels, Antonia
    ;
    Garde, Raquel
    ;
    Dromzée, Yves
    ;
    Julve, Miguel
    ;
    Sieclucka, Barbara
    ;
    Hashimoto, Kazuhito
    ;
    Okhoshi, Shin-ichi
    ;
    Verdaguer, Michel
    Nous présentons la synthèse et les propriétés structurales et magnétiques de trois nouveaux composés tridimensionnels isostructuraux, synthétisés à partir des précurseurs octacyanométallates [MIV (CN)8]−4: [MIV{(μ-CN) 4MnII (H2O)2}2•4H2O]n [MIV = NbIV (1), MoIV (2), WIV (3)]. Pour le composé 1, les propriétés magnétiques montrent l'existence d'une phase ferrimagnétique en dessous de 50 K. Par contre, les propriétés magnétiques de 2 et 3 correspondent à celles de deux ions MnII magnétiquement isolés. La seule différence électronique dans les deux types des composés est la présence de deux électrons appariés dans les ions MoIV (2) et WIV (3) (configuration électronique d2, S = 0) ce qui rend impossible une interaction d'échange avec le spin des ions MnII voisins (configuration électronique d5, S = 5/2) et d'un électron célibataire dans l'ion NbIV (1) (d1, S = 1/2) qui donne naissance à des interactions d'échange antiferromagnétiques NbIV–MnII et à l'apparition d'un ordre magnétique tridimensionnel sous la température de Curie. Ces trois composés montrent comment un électron célibataire, stratégiquement situé, peut changer de façon dramatique les propriétés magnétiques des composés par ailleurs isostructuraux., We report the synthesis, the single-crystal X-ray crystallographic structures and the magnetic properties of three new isostructural cyanido-bridged networks: [MIV{(μ-CN) 4MnII (H2O)2}2•4H2O]n [MIV = NbIV (1), MoIV (2), WIV (3)]. For compound 1, the magnetic properties reveal a ferrimagnetic phase below 50 K. In contrast, compounds 2 and 3 show a paramagnetic behaviour with no magnetic ordering down to 2 K. The only electronic difference between the two kinds of compounds is the presence of two paired electrons on MoIV (2) and WIV (3) (d2 electronic configuration, S = 0) with no possible exchange interactions with MnII ions (d5 electronic configuration, S = 5/2) and one unpaired electron on NbIV (1) (d1, S = 1/2) which allows NbIV–MnII antiferromagnetic exchange interactions and the onset of a three-dimensional magnetic ordering under Curie temperature. These three compounds demonstrate how one unpaired electron, well located, can dramatically change the magnetic behaviour of isostructural octacyanido-based three-dimensional networks.
  • Publication
    Accès libre
    Study of protonation and Zn(II), Cd(II), Cu(II) and Mn(II) complexation with a glutamic acid N-pyrimidine derivative: Crystal structure of a neutral Cd(II) complex of the bianionic ligand
    (2008)
    Arranz-Mascarós, P.
    ;
    Gutiérrez-Valero, M. D.
    ;
    López-Garzón, R.
    ;
    López-León, M. D.
    ;
    Godino-Salido M. L.
    ;
    Santiago-Medina, A.
    ;
    Stoeckli-Evans, Helen 
    The compound N-(4-amino-1-methyl-5-nitroso-6-oxo-1,6-dihydropyrimidin-2-yl)-(s)-glutamic acid (H3L) was synthesised and structurally characterised by analytical methods and 1H, 13C and 15N NMR spectroscopy. This compound (H3L) shows the same topology as other model receptors previously used to develop chemical functionalization at the surface of an active carbon when they adsorb on it. Protonation of H3L and its coordination ability towards Cd2+, Zn2+, Cu2+ and Mn2+ ions in water solution was also studied by potentiometric methods, UV–Vis and 1H, 13C NMR spectroscopies. The obtained results allow us to fit the operative conditions for the use of the activated carbon–H3L adsorbent for the retaining of the above-mentioned metal ions in aqueous solutions. The molecular structure of {[Cd(HL)H2O] • 3H2O}n was solved by single-crystal X-ray diffraction methods.
  • Publication
    Accès libre
    Ni(II) coordination compounds based on mixed phthalate and aromatic amine ligands: synthesis, crystal structures and magnetic properties
    (2005)
    Baca, Svetlana G.
    ;
    Filippova, Irina G.
    ;
    Franz, Patrick
    ;
    Ambrus, Christina
    ;
    Gdaniec, Maria
    ;
    Stoeckli-Evans, Helen 
    ;
    Simonov, Yurii A.
    ;
    Gherco, Olesea A.
    ;
    Bejan, Tanea
    ;
    Gerbeleu, Nicolae
    ;
    Decurtins, Silvio
    Three new coordination compounds, [Ni(Pht)(Py)2 (H2O)3] (1), [Ni(Pht)(β- Pic)2(H2O)3] • H2O (2) and [Ni(Pht)(1-MeIm)2 (H2O)3] (3) (where Pht2− = dianion of o-phthalic acid; Py = pyridine, β-Pic = 3-methylpyridine, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy and thermogravimetric analysis. Crystallographic studies 1–3 reveal that each Ni(II) center has a distorted octahedral geometry being coordinated by two nitrogen atoms of aromatic amines, one oxygen atom from a carboxylate group of a phthalate ligand and three water molecules. Pht2− anions act as monodentate ligands, while the remaining uncoordinated carboxylate oxygen atoms participate in the formation of hydrogen bonding. The uncoordinated oxygen atoms form hydrogen bonds with the coordinated water molecules from adjacent complexes creating a centrosymmetric dimer unit. Further, these dimer units are connected by O–HO hydrogen bonds in double-chains. Depending on the nature of aromatic amines, the arrangement of these double-chains differs. The double-chains are held together only by van der Waals interactions in 1. In contrast, in 2 these chains form layers by π–π interactions between antiparallel molecules of β-Pic as well as by π–π interactions between β-Pic and Pht aromatic rings. In complex 3, the double-chains are knitted together via C–HO hydrogen bonds between the methyl group of 1-MeIm and the coordinated carboxylate oxygen atom of Pht, as well as π–π contacts involving antiparallel 1-MeIm cycles. The thermal dependence of the magnetic susceptibilities for compounds 1 and 2 shows a weak antiferromagnetic interaction between the two Ni2+ ions of the hydrogen bonded dimers. For compound 3, a ferromagnetic interaction could be observed. Modeling the experimental data with MAGPACK resulted in: g = 2.22,
  • Publication
    Accès libre
    Protonation and Zn(II) complexation with versatile valine and glycylglycine N-pyrimidines derivatives: crystal structures of layered {[Zn(HL1)2] • 2H2O}n and [Zn(HL2)2 (H2O)4]
    (2004)
    López-Garzón, R.
    ;
    Godino-Salido M. L.
    ;
    Arranz-Mascarós, P.
    ;
    Fontecha-Cámara, M.A.
    ;
    Gutiérrez-Valero, M. D.
    ;
    Cuesta, R.
    ;
    Moreno, J.M.
    ;
    Stoeckli-Evans, Helen 
    Protonation and Zn(II) complexation of N-substituted amino acids, valine (H2L1) and glycylglycine (H2L2), with 4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidin-2-yl as substituent, were studied by potentiometric and UV–Vis measurements. Bianions L1 and L2 suffer three protonation steps in aqueous medium corresponding to the amide and carboxylate groups of the amino acidic moiety, and the nitrogen atom of the nitroso group of the pyrimidine fragment. Both ligands form mononuclear Zn(II) complexes in aqueous solutions. The binding donor groups are the nitroso and/or the oxo groups of the pyrimidinic moiety or the carboxylate group, depending on whether the ligands are neutral or anionic, respectively. Weak metal-to-ligand interactions were observed independently of the functionality used by the corresponding ligand on bonding to Zn(II). The reaction of ZnCl2 with the monodeprotonated ligands (1:1) yields a polynuclear 2D {[Zn(HL1)2] • 2H2O}n and a mononuclear [Zn(HL2)2(H2O)4] complexes, showing the influence of the susbtituent on the amino acids fragment as well as the versatility of this class of compounds when acting as ligands.
  • Publication
    Accès libre
    Organosulfur donor with hydroxy groups and its conducting salt: crystal structures and physical properties
    (2004)
    Liu, Shi-Xia
    ;
    Neels, Antonia
    ;
    Stoeckli-Evans, Helen 
    ;
    Pilkington, Melanie
    ;
    Wallis, John D.
    ;
    Decurtins, Silvio
    Crystal structures of organosulfur donor 2-(5′,6′-dihydro[1,3]dithiolo[4,5-b][1,4]-dithiin-2′-ylidene)-6,7-di-hydro-5H-[1,3]dithiolo[4,5-b][1,4]dithiepine-6,6-dimethanol (D) and its conducting salt D2I3 are described. Conductivity properties of D2I3 are also discussed.