A family of dodecanuclear Mn(11)Ln single-molecule magnets
Résumé
A series of four isostructural dodecanuclear complexes [Mn(III)9Mn(II)2Ln(III)(0)(8)(OH)(Piv)(16) (NO3)(CH3CN)]center dot xCH(3)CN center dot yC(7)H(16) (piv = pivalate; x = 1/2, y = Ln = Tb (1); x = 2, y = 1/2, Ln = Dy (2), Ho (3), and Y (4)) has been prepared for which the structural motif described as 'a lanthanide ion nested in a large manganese shell' is observed. All compounds show out-ofphase signals in their ac susceptibilities, and their single-molecule magnet behaviour was confirmed by single-crystal micro-SQUID studies of 1-3 which show hysteresis loops of molecular origin at T < 1.0 K. The SMM behaviour observed in compounds 1-3 is more pronounced than that for 4, which contains the diamagnetic Yu(III) ion. This is principally the result of ferromagnetic coupling between the paramagnetic anisotropic Le(III) ions (Tb-III. Dy-III and Hot(III)) and the manganese shell, which enhances the total spin ground state of the complexes. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.