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)

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 mu (3)-O ions, sixteen XCH2CO2- units and four terminal water molecules, as well as included CH2Cl2 and H2O. Different arrangements of the four Mn(III) 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. chi'T-m values for complexes 1 and 2, where chi'(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 chi'T-m. Their chi'(m) signals measured at different frequencies are observed in the region 2-10 K, and exhibit a frequency dependency on the chi'(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.