A Wheel‐Shaped Single‐Molecule Magnet of [Mn^II₃Mn^III₄]: Quantum Tunneling of Magnetization under Static and Pulse Magnetic Fields

Abstract

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 [MnII 3MnIII 4(5-NO2-hbide)6].5 C2H4Cl2 (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 chimT 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 0 4 were estimated to be -0.283(1) K and -1.64(1)x10(-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 (DeltaE) of 18.1 K and a pre-exponential factor of 1.63x10(-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.

Magnetic anisotropy in trigonal planar Fe(ii) bis(trimethylsilyl)amido complexes of the type [Fe{N(SiMe3)2}2L]—experiment and theory

“…This effect can in 1-3 be ascribed to a lifting of degeneracy of the electronic states by the dc field which impedes relaxation processes via Quantum Tunneling (QTM). 23,24 In contrast, the absence of slow relaxation of magnetization for complex 4 is in line with a smaller magnitude of D and less axial anisotropy expressed by its g-factors (Table 3) being not sufficient to establish a significant intrinsic barrier for reversal of the magnetization. This is similar to the behavior of 6.…”

Trinuclear [CoIII2–LnIII] (Ln=Tb, Dy) Single‐Ion Magnets with Mixed 6‐Chloro‐2‐Hydroxypyridine and Schiff Base Ligands

“…The magnetic relaxation process of the SMMs/SIMs may partially be influenced by quantum effects, and the application of a dc field probably removes the ground-state degeneracy, which induces quantum-tunneling effects. [14] After applying a dc field of 2000 Oe, both the c' and c'' signals of 1 were strongly frequency dependent below 30 K and good peak shapes were observed (Figure 3). The parameter f= (DT f /T f )/DA C H T U N G T R E N N U N G (logf) (f denotes the frequency) was Figure 2.…”

Ferromagnetic cluster spin waves in molecular disks studied by inelastic neutron scattering

“…In this work, mixed-valence Mn III 3 Mn II 4 disks (or Mn 7 disks in short) will be considered, in which a Mn II (spin S i = 5/2) ion is sitting at the center, and the remaining three Mn II (S i = 5/2) and Mn III (S i = 2) ions are positioned alternately on the outer hexagon. [28][29][30][31][32] The large majority of Mn 7 disks possess a ground-state spin of S = 11, which can be rationalized as follows: The spins on the six outer ions are aligned parallel to each other but antiparallel to the spin on the central ion, as indicated in Fig. 1(a).…”