Gadolinium is a special case in spectroscopy because
of the near
isotropic nature of the 4f7configuration of the +3 oxidation
state. Gd3+complexes have been studied in several symmetries
to understand the underlying mechanisms of the ground state splitting.
The abundance of information in Gd3+spectra can be used
as a probe for properties of the other rare earth ions in the same
complexes. In this work, the zero-field splitting (ZFS) of a series
of Gd3+pentagonal bipyramidal complexes of the form [GdX1X2(Leq)5]n+[n= 1, X = axial ligands: Cl–,–OtBu,–OArF5orn= 3, X =tBuPO(NHiPr)2, Leq= equatorial ligand: Py, THF or H2O] with near
fivefold symmetry axes along X1-Gd-X2was investigated.
The ZFS parameters were determined by fitting of room-temperature
continuous wave electron paramagnetic resonance (EPR) spectra (at
X-, K-, and Q-band) to a spin Hamiltonian incorporating extended Stevens
operators compatible withC5symmetry.
Examination of the acquired parameters led to the conclusion that
the ZFS is dominated by theB20term and that the magnitude ofB20is almost entirely dependent on, and inversely proportional to,
the donor strength of the axial ligands. Surveying the continuous
shape measure and the X1-Gd-X2angle of the
complexes showed that there is some correlation between the proximity
of each complex toD5hsymmetry and the magnitude of theB65parameter, but
that the deformation of the X1-Gd-X2angle is
more significant than other distortions. Finally, the magnitude ofB20was found to be inversely proportional to the thermal barrier for
the reversal of the magnetic moment (Ueff) of the corresponding isostructural Dy3+complexes.