posted on 2020-03-09, 14:04authored byMichael J. Colaneri, Simon J. Teat, Jacqueline Vitali
Electron paramagnetic resonance and
crystallographic studies on
copper-doped cadmium creatininium sulfate (CdCrnS) were undertaken
to study the characteristics of a copper-hexahydrate complex in an
organic analogue of Tutton’s salt. X-ray diffraction experiments
determined the crystal structure of CdCrnS at both 100 and 298 K.
CdCrnS, like Tutton salt, crystallizes in the monoclinic space group P21/n. The unit cell contains
two cadmium hexahydrate complexes, four creatininium ions, four sulfates,
and four additional solvation waters. Both crystallography and EPR
find that the doped copper replaces the cadmium in the structure.
Single-crystal EPR measurements at room temperature determined the g and copper hyperfine (ACu) tensors
(principal values: g = 2.437, 2.134, and 2.080 and ACu = −327, −84.8, and 7.33 MHz).
EPR spectra of the powder at room temperature gave g =
2.448, 2.125, and 2.085 and ACu = −315,
−75.0, and 35.0 MHz and at 110 K gave g = 2.462,
2.116, and 2.077 and ACu = −340, −30.0,
and 35.0 MHz. The room-temperature tensors are close to the “rigid
lattice limit” values found in copper-doped Tutton salts but
with a higher gmin and weaker ACux coupling than average.
A small but measurable temperature dependency of the tensors indicated
the presence of a dynamic Jahn-Teller (JT) effect. In addition, the
EPR line width changed dramatically with temperature, which is like
that found in all copper-doped Tutton crystals. Utilizing the model
of Silver–Getz for the g-value variation gave
an estimate for the energy difference (δ12 = 640
cm–1) between the ground and next highest JT configurations.
An empirical correlation appears to exist between δ12 and gmin and ACux for the copper hexahydrates studied
in similar crystals. This suggests a relationship between the amount
of unpaired spins in the copper d-orbital x lobe
and the gap between wells of the adiabatic potential surface.