Mixed 3d/4d and 3d/4f metal clusters:: Tetranuclear FeIII2MIII2 (MIII = Ln, Y) and MnIV2MIII2 (M = Yb, Y) complexes, and the first Fe/4f single-molecule magnets

The synthesis, structure and magnetic properties are reported of Fe(2)Ln(2), Fe2Y2, Mn2Yb2 and Mn2Y2 complexes. The compound [Fe2Ho2(OH)(2)(teaH)(2)(O2CPh)(4)(NO3)(2)] (1), where teaH(3) is triethanolamine, was obtained from the reaction of eight equivalents of teaH(3) 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)(6)Cl-4]Cl-2 (4) and isostructural [Fe2Ho2(pdmH)(6)Cl-4]Cl-2 (5), where pdmH(2) is pyridine-2,6-dimethanol, were prepared from the reaction of four equivalents of pdmH(2) 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' M-4 core (including the first mixed 3d/4f examples of this type to contain Fe-III or Mn-IV), 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 I and 2 are the first examples of Fe/4f SMMS. (c) 2005 Elsevier Ltd. All rights reserved.