Heterometallic [Mn5-Ln4] single-molecule magnets with high anisotropy barriers

ne reaction of [Mn6O2- (Piv)(10)(4-Me-py)(2.5)(PivH)(1.5)] (1) (py: pyridine, Piv: pivilate) with N-methyl-diethanolamine (mdeaH(2)) and Ln(NO3)(3)center dot 6H(2)O in MeCN leads to a series of nonanuclear compounds [Mn(5)Ln(4)(O)(6)(mdea)(2)(mdeaH)(2)(PiV)(6)-(NO3)(4)(H2O)(2)]center dot 2MeCN (Ln=Tb-III (2), Dy-III(3), Ho-III (4), Y-III (5)). Single-crystal X-ray diffraction shows that compounds 2-5 are isostructural, with the central core composed of two dis-totted [Mn(IV)Mn(III)Ln(2)O(4)] cubanes sharing a Mn-IV 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 Delta(eff) and tau(0) for 3 of 38.6K and 3.0x10(-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 mu-SQUID measurements on an oriented single crystal and the observation of M versus H hysteresis loops below 1.9 K.