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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
    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
    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,