Vignette d'image

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

Résultat de la recherche

Filtres

2
2
2
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 2 sur 2
  • 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
    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,