Structural and Electronic Dependence of the Single-Molecule-Magnet Behavior of Dysprosium(III) Complexes

We investigate and compare the magnetic
properties of two isostructural DyIII-containing complexes.
The DyIII ions are chelated by hexadentate ligands and
possess two apical bidendate nitrate anions. In dysprosium­(III) N,N′-bis­(imine-2-yl)­methylene-1,8-diamino-3,6-dioxaoctane
(1), the ligand’s donor atoms are two alkoxo,
two pyridine, and two imine nitrogen atoms. Dysprosium­(III) N,N′-bis­(amine-2-yl)­methylene-1,8-diamino-3,6-dioxaoctane
(2) is identical with 1 except for one modification:
the two imine groups have been replaced by amine groups. This change
has a minute effect on the structure and a larger effect the magnetic
behavior. The two complexes possess slow relaxation of the magnetization
in the presence of an applied field of 1000 Oe but with a larger barrier
for reorientation of the magnetization for 1 (Ueff/kB = 50 K) than
for 2 (Ueff/kB = 34 K). First-principles calculations using the spin–orbit
complete active-space self-consistent-field method were performed
and allowed to fit the experimental magnetization data. The calculations
gave the energy spectrum of the 2J + 1 sublevels
issued from the J = 15/2 free-ion
ground state. The lowest-lying sublevels were found to have a large
contribution of MJ =
±15/2 for 1, while for 2, MJ = ±13/2 was dominant. The observed differences were
attributed to a synergistic effect between the electron density of
the ligand and the small structural changes provoked by a slight alteration
of the coordination environment. It was observed that the stronger
ligand field (imine) resulted in complex 1 with a larger
energy barrier for reorientation of the magnetization than 2.