Heterometallic Mn5‐Ln4 Single‐Molecule Magnets with High Anisotropy Barriers

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 x 6 H2O in MeCN leads to a series of nonanuclear compounds Mn5Ln4 (O) 6 (mdea) 2 (mdeaH) 2 (Piv) 6 (NO3) 4 (H2O) 22 MeCN (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 distorted Mn (IV) Mn (III) Ln2O4 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 (o) for 3 of 38. 6 K and 3. 0 x 10 (-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.