Abstract of Publication No. 580
Satoshi Koizumi, Masayuki Nihei, Takuya Shiga, Motohiro Nakano, Hiroyuki Nojiri,
Roland Bircher, Oliver Waldmann, Stefan T. Ochsenbein, Hans U. Güdel, Felix Fernandez-Alonso and Hiroki Oshio
The reaction of N-(2-hydroxy-5-nitrobenzyl)iminodiethanol (=H3(5-NO2-hbide))
with Mn(OAc)2·4 H2O in methanol, followed by recrystallization from
1,2-dichloroethane, yielded a wheel-shaped single-molecule magnet (SMM) of
(1). In 1, seven manganese ions are linked by six tri-anionic
ligands and form the wheel in which the two manganese ions on the rim and the
one in the center are MnII and the other four manganese ions are MnIII
ions. Powder magnetic susceptibility measurements showed a gradual increase with
values as the temperature was lowered, reaching a maximum value of 53.9 emu mol–1 K.
Analyses of magnetic susceptibility data suggested a spin ground state of S=19/2.
The zero-field splitting parameters of D and B
were estimated to be -0.283(1) K and -1.64(1)×10–5 K, respectively,
by high-field EPR measurements (HF-EPR). The anisotropic parameters agreed with
those estimated from magnetization and inelastic neutron scattering experiments.
AC magnetic susceptibility measurements showed frequency-dependent in- and
out-of-phase signals, characteristic data for an SMM, and an Arrhenius plot of
the relaxation time gave a re-orientation energy barrier (DE)
of 18.1 K and a pre-exponential factor of 1.63×10–7 s. Magnetization
experiments on aligned single crystals below 0.7 K showed a stepped hysteresis
loop, confirming the occurrence of quantum tunneling of the on magnetization (QTM).
QTM was, on the other hand, suppressed by rapid sweeps of the magnetic field
even at 0.5 K. The sweep-rate dependence of the spin flips can be understood by
considering the Landau-Zener-Stückelberg (LZS) model.