Heterometallic [Mn5-Ln4] Single-Molecule Magnets with High Anisotropy Barriers
Résumé
The reaction of [Mn6O2-(Piv)10(4-Me-py)2.5(PivH)1.5] (1) (py: pyridine, Piv: pivilate) with N-methyldiethanolamine (mdeaH2) and Ln(NO3)3*6H2O in MeCN leads to a series of nonanuclear compounds [Mn5Ln4(O)6ACHTUNGTRENUNG(mdea)2(mdeaH)2(Piv)6- (NO3)4(H2O)2]*2MeCN (Ln=TbIII (2), DyIII (3), HoIII (4), YIII (5)). Single crystal X-ray diffraction shows that compounds 2-5 are isostructural, with the central core composed of two distorted {MnIVMnIIILn2O4} cubanes sharing a MnIV vertex, representing a new heterometallic 3d-4f motif for this class of ligand. The four new compounds display single-molecule magnet (SMM) behaviour, which is modulated by the lanthanide ion used. Moreover, the values found for Deff and to for 3 of 38.6 K and 3.0310-9 s respectively reveal that the complex 3 exhibits the highest energy barrier recorded so far for 3d-4f SMMs. The slow relaxation of the magnetisation for 3 was confirmed by m-SQUID measurements on an oriented single crystal and the observation of M versus H hysteresis loops below 1.9 K.