Synthesis, X-ray characterization and single molecule magnetic behaviour of [Mn12O12(O2CCH2X)16(H2O)4]·mCH2Cl2·nH2O (1: X = Cl, m = 2, n = 6; 2: X = Br, m = 4, n = 0)

Abstract

Two new complexes, 1 and 2, with halo acetate ligands have been prepared from the reaction of ClCH₂CO₂H or BrCH₂CO₂H with the precursor Mn12Ac, and their structures and magnetic properties studied. The structures of complexes 1 and 2 consist of a central cubane-like [Mn₄O₄]⁸⁺ unit held within a non-planar ring of eight Mn(III) ions by eight μ₃-O ions, sixteen XCH₂CO₂⁻ units and four terminal water molecules, as well as included CH₂Cl₂ and H₂O. Different arrangements of the four Mn(IV) atoms relative to the eight Mn(III) atoms in the title complexes and other comparable complexes could play a role in the observed magnetic properties. Five and three periodic steps in the magnetic hysteresis loops are observed for both 1 and 2 at 2.2 and 2.6 K, respectively. χ′_mT values for complexes 1 and 2, where χ′_m is the in-phase component of the AC magnetic susceptibility, exhibit a plateau in the 6–20 K region, below which there is an abrupt decrease in χ′_mT. Their χ″_m signals measured at different frequencies are observed in the region 2–10 K, and exhibit a frequency dependency on the χ″_m AC peaks, with a predominant peak in the 4–10 K region. For these complexes, there is a difference between the zero-field-cooled (ZFC) and the field-cooled (FC) magnetization due to slow relaxation of the magnetization.