Structures and magnetic properties of MnIII4LnIII4 aggregates with a “square-in-square” topology

Abstract

The structures and magnetic properties of a family of new octanuclear heterometallic 3d-4f complexes [Mn^III₄Ln^III₄(μ₃-OH)₄(μ₂,η¹-X)₄(O₂CBu^t)₈(t-bdea)₄]·solv, where X = N₃⁻, Ln = Y (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6); X = OCN⁻, Ln = Dy (7); X = NO₃⁻, Ln = Gd (8), Tb (9), Dy (10), Ho (11), Er (12); solv = MeCN or toluene, are reported. The metal topology in the aggregates can be described as consisting of a “Ln₄-square inscribed in a Mn₄-square”. Complexes 1-7 are prepared by the reactions of t-butyldiethanolamine (t-bdeaH₂) with a preformed hexanuclear manganese pivalate complex [Mn₆], the respective lanthanide salt and either NaN₃ or NaNCO, while 8-12 are obtained from the direct reaction of Mn(OAc)₂, Ln(NO₃)₃·xH₂O and t-butyldiethanolamine. The magnetic properties of all the complexes were investigated using variable temperature magnetic susceptibility and magnetisation measurements. Similar magnetic behaviour was observed for compounds containing the same lanthanide, indicating that changing the bridging ligand X does not have a significant effect on the magnetic behaviour. The Tb^III and Dy^III compounds 4, 5, 7, 9 and 10 all show frequency-dependent ac susceptibilities indicative of a slow relaxation of magnetisation and are therefore considered as Single-Molecule Magnets.