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Stoeckli-Evans, Helen

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

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  • Publication
    Accès libre
    Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-MeIm): [Mn3III0(02CCMe3)6 (Im)3](Me3CC02)•0.5Me3CC02H and [Mn2IIIMnII0(02CCMe3)6(1-MeIm)3]
    (2006)
    Baca, Svetlana G.
    ;
    Stoeckli-Evans, Helen 
    ;
    Ambrus, Christina
    ;
    Malinovskii, Stanislav T.
    ;
    Malaestean, Iurii
    ;
    Gerbeleu, Nicolae
    ;
    Decurtins, Silvio
    Two new μ3-oxo-centered trinuclear manganese complexes, one of them a homo-valence [Mn3III0(02CCMe3)6 (Im)3](Me3CC02)•0.5Me3CC02H (1) pivalate complex and the other a mixed-valence [Mn2IIIMnII0(02CCMe3)6(1-MeIm)3] (2) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, X-ray crystallography and magnetochemistry. Complexes 1 and 2 are μ3-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (1) or 1-MeIm (2) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-MeIm nitrogen atom. The crystal packing of 1 involves hydrogen bonding between complex cations [Mn3O(Piv)6(Im)3]+ and outersphere pivalate ions, whereas in compound 2 interactions of the C–Hπ type, formed by both the aromatic and methyl C–H groups of 1-MeIm molecules, are present. Magnetic studies reveal that both compounds represent antiferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants.
  • 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
    Synthesis, structure and magnetic properties of cobalt(II) and copper(II) coordination polymers assembled by phthalate and 4-methylimidazole
    (2004)
    Baca, Svetlana G.
    ;
    Malinovskii, Stanislav T.
    ;
    Franz, Patrick
    ;
    Ambrus, Christina
    ;
    Stoeckli-Evans, Helen 
    ;
    Gerbeleu, Nicolae
    ;
    Decurtins, Silvio
    New coordination polymers [M (Pht)(4-MeIm)2 (H2O)]n (M=Co (1), Cu (2); Pht2−=dianion of o-phthalic acid; 4-MeIm=4-methylimidazole) have been synthesized and characterized by IR spectroscopy, X-ray crystallography, thermogravimetric analysis and magnetic measurements. The crystal structures of 1 and 2 are isostructural and consist of [M (4-MeIm)2(H2O)] building units linked in infinite 1D helical chains by 1,6-bridging phthalate ions which also act as chelating ligands through two O atoms from one carboxylate group in the case of 1. In complex 1, each Co(II) atom adopts a distorted octahedral N2O4 geometry being coordinated by two N atoms from two 4-MeIm, three O atoms of two phthalate residues and one O atom of a water molecule, whereas the square-pyramidal N2O3 coordination of the Cu(II) atom in 2 includes two N atoms of N-containing ligands, two O atoms of two carboxylate groups from different Pht, and a water molecule. An additional strong O–HO hydrogen bond between a carboxylate group of the phthalate ligand and a coordinated water molecule join the 1D helical chains to form a 2D network in both compounds. The thermal dependences of the magnetic susceptibilities of the polymeric helical Co(II) chain compound 1 were simulated within the temperature range 20–300 K as a single ion case, whereas for the Cu(II) compound 2, the simulations between 25 and 300 K, were made for a linear chain using the Bonner–Fisher approximation. Modelling the experimental data of compound 1 with MAGPACK resulted in: g=2.6,