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 Mn4 by eight µ3-O ions, sixteen XCH2CO2 units and four terminal water molecules, as well as included CH2Cl2 and H2O. Dierent arrangements of the four Mn4 relative to the eight Mn4 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 2.6K, respectively.χmT values for complexes 1 and 2, where χm is the in-phase component of the AC magnetic susceptibility, exhibit a plateau in the 6-20K region, below which there is an abrupt decrease in χmT. Their χm signals measured at different frequencies are observed in the region 2-10 K, and exhibit a frequency dependency on the χm AC peaks, with a predominant peak in the 4-10K 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.

The magnetic exchange interaction behavior and energy spectrum of low-lying spin states are investigated by using ab initio multireference configuration-interaction method for the representative binuclear transition-metal complexes fsNH3d5Crs m-OHdCrsNH3d5g5+ and fCl3FeOFeCl3g2−. Our calculations for the nonmodeling real title complexes found that under the appropriate basis sets and active space, ab initio method at multireference configuration-interaction level of theory is able to give accurate energy spectrum of low-lying spin states within reachable computation demand nowadays and the deviation of magnetic exchange interaction to Lande interval rule can be described by the biquadratic correction in terms of Heisenberg spin Hamiltonian. As a methodology comparison, density-functional theory combined with broken-symmetry approach provides an alternative yet efficient approach to produce accurate numerical results, but there are dependences on the particular chosen exchange-correlation functionals and system dependent. The spin population analyses at complete active space self-consistent-field level of the theory provide an instructively understanding and prediction for the magnetic interaction mechanism.