Distorted Mn(IV)Mn(III)₃ cubane complexes as single-molecule magnets

Alternating current (ac) magnetic susceptibility data are presented for six distorted cubane complexes of the composition [Mn(IV)Mn(III)₃O₃X]. Each of these complexes has a well isolated S = 9/2 ground state. There is zero-field splitting (ZFS) in the ground states where D, the axial ZFS parameter, is found to be in the range of -0.27 to -0.38 cm^-1. As a result of the big spin ground state and appreciable magnetic anisotropy, an out-of-phase ac magnetic susceptibility signal is seen for each of the six Mn₄ complexes. The out-of-phase ac susceptibility signal reflects slow magnetization relaxation which is taken to indicate that individual molecules are acting as magnets. Alternating current susceptibility data are presented for a frozen glass of one of the Mn₄ complexes to confirm that the out-of-phase ac signal is associated with isolated molecules. The factors that influence whether a given complex can function as a single-molecule magnet are described. The above Mn₄ complexes represent only the second type of molecules that exhibit enough magnetic anisotropy to function as single-molecule magnets.