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Liquid-crystalline Single Molecule Magnets
Single Molecule Magnets (the archetype of which is the so-called "Mn12", a polymetallic Mn complex, of formula [Mn12O12(OAc)16(H2O)4]) have the remarkable property of showing an extremely slow relaxation of their magnetization below a blocking temperature (D. Gatteschi, R. Sessoli, Angew. Chem. Int. Ed. 2003, 42, 268-297 and references therein). This hysteresis of purely molecular origin allows foreseeing the ultimate scale of information storage a single molecule. Moreover, the quantum tunnelling of the magnetization, observed on these molecules, may open huge opportunities on the way to quantum computing. Nevertheless, the most important challenges before the eventual use of this type of molecules in a quantum computer remain their self-organization and their addressing.
Chemists from the icFRC have recently reported for the first time the endowment of the Mn12 with liquid-crystalline phases by functionalizing the Mn12 with mesogenic ligands. Depending on the characteristics of the mesogenic ligands (size and position of the substituting groups), clusters possessing f
luid mesophases with 3D (cubic) or 1D (smectic) positional order have been obtained. Even though short ranged, the intra-layer ordering of the molecular cores in the smectic phase is square-like. The magnetic properties are preserved upon functionalization and the molecules are thermally stable up to 150 °C. Another very interesting result is the fact that the main molecular axes of the magnetic cores share a common alignment direction, in a nematic sense.
luid mesophases with 3D (cubic) or 1D (smectic) positional order have been obtained. Even though short ranged, the intra-layer ordering of the molecular cores in the smectic phase is square-like. The magnetic properties are preserved upon functionalization and the molecules are thermally stable up to 150 °C. Another very interesting result is the fact that the main molecular axes of the magnetic cores share a common alignment direction, in a nematic sense.It seems reasonable to expect that these remarkable features may facilitate the 2D ordering of these clusters on surfaces, which is the ultimate goal. In order to tailor more precisely the mesomorphic behaviour of these SMMs, the modification of the ligand structure as well as the regioselective substitution of two different ligands (at the axial and equatorial positions) are currently in progress.
Picture: View of the crystal structure of a "Mn12" derivative obtained at the IPCMS (left), simulated views (in accordance with the XRD data) of the lamellar organisation of the molecules and their substituants in the smectic phase (middle) and hysteresis curves for different liquid-crystalline "Mn12" molecules (right).
Emmanuel Terazzi, Cyril Bourgogne, Richard Welter, Jean-Louis Gallani, Daniel Guillon, Guillaume Rogez, Bertrand Donnio, « Single-Molecule Magnets with Mesomorphic Lamellar Ordering”, Angew. Chem. Int. Ed., 2008, 47, 3, 490-495 link to article
