NUCLEAR-SPIN RELAXATION IN PARAMAGNETIC-COMPLEXES IN THE SLOW-MOTION REGIME FOR THE ELECTRON-SPIN - THE ANISOTROPIC PSEUDOROTATION MODEL FOR S=1 AND THE INTERPRETATION OF NUCLEAR MAGNETIC-RELAXATION DISPERSIONRESULTS FOR A LOW-SYMMETRY NI(II) COMPLEX
T. Larsson et al., NUCLEAR-SPIN RELAXATION IN PARAMAGNETIC-COMPLEXES IN THE SLOW-MOTION REGIME FOR THE ELECTRON-SPIN - THE ANISOTROPIC PSEUDOROTATION MODEL FOR S=1 AND THE INTERPRETATION OF NUCLEAR MAGNETIC-RELAXATION DISPERSIONRESULTS FOR A LOW-SYMMETRY NI(II) COMPLEX, The Journal of chemical physics, 101(2), 1994, pp. 1116-1128
This work presents the anisotropic pseudorotation (APR) model, which i
s a new dynamic model for the interpretation of experimental nuclear s
pin-lattice relaxation times in paramagnetic (S=1) complexes of low sy
mmetry. It comprises two dynamic processes active in modulating the ze
ro-field splitting interaction (ZFS). Reorientation of the complex mod
ulates a static zero-field splitting, defined as a measure of the asym
metry in the equilibrium geometry at the paramagnetic site. Local moti
ons of the ligands surrounding the paramagnetic site further contribut
e a rapidly fluctuating (transient) zero-field splitting interaction.
This dynamic model is evaluated within a general theoretical framework
capable of dealing with the electron-spin system in the low- and high
-magnetic field limits for both Redfield and slow-motion cases, i.e.,
where the motions: inducing electron-spin relaxation and the electron-
spin relaxation itself are characterized by the same time scale. The d
ynamic model is characterized and discussed by calculating results for
a large number of parameter sets. The obtained results are compared w
ith the traditional theory, the Solomon-Bloembergen-Morgan equations (
SBM), by least-squares fitting the SBM equations to the APR model. Res
ults show that in most cases the SBM model can fit the nuclear magneti
c relaxation dispersion (NMRD) profiles from the APR model at the expe
nse of using a different parameter set. For both models, a restricted
fit to-experimental NMRD data, from amethyl-3,5-heptanedionato)Ni(II)(
aniline-d(5))(2) (abbreviated Ni(dpm)(2)(aniline-d(5))(2) or simply NI
DPM) in solution, has been performed. The parameters obtained suggest
that NIDPM is a slow-motion case comprising a static contribution to i
ts zero-field splitting, so that the SBM model is inapplicable.