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Single Molecule Magnets Go Supramolecular : Exchange-biased Quantum Tunnelling in Chains and Metal-Organic Frameworks

Mardi 25 octobre 2016 13:30 - Duree : 1 heure
Lieu : LNCMI, salle de conférences "René Pauthenet" (bâtiment J, 2ème étage) - 25 rue des martyrs - 38000 Grenoble

Orateur : Andrea CORNIA (University of Modena and Reggio Emilia, Italy)

Molecules exhibiting a directionally-bistable magnetic moment can be assembled into topologically well-defined arrays of various dimensionality, ranging from dimers to chains and metal-organic frameworks (MOFs).(1) Intermolecular superexchange interactions, when operative, may shift the hysteresis loops of these materials along the field axis, leading to higher magnetic remanence. We herein use a tetrairon(III) complex (S = 5) functionalized with two 4-pyridyl groups (Fe4) as a 180°-ditopic supramolecular synthon to assemble MOFs and chain-like compounds. Its reaction with silver(I) perchlorate affords an unprecedented diamondoid structure with silver(I) ions as tetrahedral nodes and Fe4 complexes as linear linkers. The cubic lattice comprises four magnetically distinct Fe4 units with anisotropy axes directed along the threefold axes of AgN4 tetrahedra. The resulting highly-noncollinear magnetic structure has no second-order magnetic anisotropy, but retains magnetic bistability.(2) Of special relevance is the construction of supramolecular ensembles where magnetic intermolecular interactions are susceptible of chemical control. To this aim, complex [Ru2(OAc)4] (s = 1) and its one-electron oxidized variant [Ru2(OAc)4]+ (s = 3/2) are used to line up Fe4 complexes into alternating chains. Since both diruthenium species have a huge hard-axis anisotropy, spin-parity effects result in dramatically different magnetic properties at low T. While the ground state of [Ru2(OAc)4] is a nonmagnetic singlet, [Ru2(OAc)4]+ exhibits Kramers degeneracy and behaves as an effective s’ = 1/2 spin. By coupling antiferromagnetically to the neighbouring Fe4 complexes, it promotes a ferromagnetic alignment of their S = 5 spins giving rise to a rich quantum dynamics with strongly exchange-biased hysteresis loops (0.12 T) and enhanced stability of zero-field magnetization.(3)

(1) K. Liu, X. Zhang, X. Meng, W. Shi, P. Cheng, A. K. Powell, Chem. Soc. Rev. 2016, 45, 2423.

(2) L. Rigamonti, C. Cotton, A. Nava, H. Lang, T. Rüffer, M. Perfetti, L. Sorace, A.-L. Barra, Y. Lan, W. Wernsdorfer, R. Sessoli, A. Cornia, Chem. Eur. J. DOI : 10.1002/chem.201601383.

(3) A. Nava, L. Rigamonti, E. Zangrando, R. Sessoli, W. Wernsdorfer, A. Cornia, Angew. Chem. Int. Ed. 2015, 54, 8777.

Contact : anne-laure.barra@lncmi.cnrs.fr

Discipline évènement : (Physique)
Entité organisatrice : (LNCMI)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire LNCMI)
Site de l'évènement : Polygone scientifique

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