Mixed 3d/4d and 3d/4f metal clusters: Tetranuclear Fe2IIIM2III(MIII=Ln,Y) and Mn2IVM2III(M=Yb,Y) complexes, and the first Fe/4f single-molecule magnets

The synthesis, structure and magnetic properties are reported of Fe2Ln2, Fe2Y2, Mn2Yb2 and Mn2Y2 complexes. The compound [Fe2Ho2(OH)2(teaH)2(O2CPh)4(NO3)2] (1), where teaH3 is triethanolamine, was obtained from the reaction of eight equivalents of teaH3 with one equivalent each of Ho(NO3)3 and [Fe3O(O2CPh)6(H2O)3](O2CPh) in MeCN/MeOH. The use instead of Dy(NO3)3 or Tb(NO3)3 leads to the structurally similar products [Fe2Dy2(OH)2(teaH)2(O2CPh)6] (2) and [Fe2Tb2(OH)2(teaH)2(O2CPh)6] (3). The compounds [Fe2Y2(pdmH)6Cl4]Cl2 (4) and isostructural [Fe2Ho2(pdmH)6Cl4]Cl2 (5), where pdmH2 is pyridine-2,6-dimethanol, were prepared from the reaction of four equivalents of pdmH2 with two equivalents of YCl3 or HoCl3, respectively, and FeCl2 in MeOH. The compounds [Mn2Y2O2(O2CPh)6(OMe)4(MeOH)4] (6) and [Mn2Yb2O2(O2CPh)6(OMe)4(MeOH)4] (7) were prepared by methanolysis of (NBu4n)-[Mn4O2(O2CPh)9(H2O)]in the presence of Yb(NO3)3 or Y(NO3)3, respectively. Complexes 1–3, 6 and 7 contain a ‘defect dicubane’ M4 core (including the first mixed 3d/4f examples of this type to contain FeIII or MnIV), whereas 4 and 5 have a U-shaped core. Variable-temperature solid-state magnetic susceptibility studies of 1–6 in the temperature range 5.00–300 K were carried out, and for all the complexes predominantly antiferromagnetic exchange interactions between the metal centers was observed. Magnetization versus applied field sweeps on single crystals of 1 and 2 at low temperature reveal hysteresis loops, confirming these species to be new examples of single-molecule magnets (SMMs). Thus, complexes 1 and 2 are the first examples of Fe/4f SMMs.

Mixed 3d/4d and 3d/4f tetranuclear complexes have been synthesized, comprising Fe2Ln2, Fe2Y2, Mn2Yb2 and Mn2Y2 clusters. The compounds were prepared by using triethanolamine, pyridine-2,6-dimethanol, or methanolysis conditions. The Fe2Ln2 (Ln = HoIII, DyIII) were found to be single-molecule magnets (SMMs) by low temperature, single crystal hysteresis studies, and these complexes thus represent the first mixed-metal Fe/Ln SMMs to be discovered.Figure optionsDownload as PowerPoint slide