[Ln(III)-Mn-II-Ln(III)] heterometallic compounds: rare linear SMMs with divalent manganese ions

The reaction of Mn(OAc)(2)center dot 4H(2)O and Ln(NO3)(3)center dot 6H(2)O with N-(2-aminopropyl)-2-hydroxybenzamide and salicylic aldehyde in methanol/methylene dichloride produces yellow crystals of Ln(2)Mn(C7H5O2)(8) (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)), in the presence of triethylamine. Three metal ions are connected by six mu(2)-phenolate oxygen atoms of six salicylic aldehyde ligands, resulting in perfect linear [Ln(III)-Mn-II-Ln(III)] structures. Magnetic studies of these complexes have been performed and AC susceptibility measurements show the presence of a temperature-dependent out-of-phase ac signal for complexes 2 and 3 indicating single-molecule magnet (SMM) behavior. The (Dy2MnII)-Mn-III compound shows double relaxation pathways which may originate from the single ion behavior of individual Dy-III ions and the weak coupling between Dy-III and Mn-II ions, respectively. The U-eff of 92.4(2) K is a relatively high value among 3d-4f SMMs. Moreover, complexes 2 and 3 represent the first linear Mn-Ln SMMs containing only divalent manganese ions as far as we know. The result suggests the positive effects of magnetic coupling to enhance their SMM behavior, presenting a promising strategy for constructing efficient heterometallic SMMs