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Download fileMolecular Motion of the Bis(maleonitriledithiolato)nickel Trianion in Solution
journal contribution
posted on 2012-07-05, 00:00 authored by Bruce A. Kowert, Ann B. J. Stemmler, Timothy
L. Stemmler, Steven J. Gentemann, Michael B. Watson, Vanessa S. GoodwillElectron spin resonance (ESR) has been used to study
the reorientational
motion of the bis(maleonitriledithiolato)nickel trianion, [Ni(mnt)2]3–, in diethylene glycol dimethyl ether
(diglyme). [Ni(mnt)2]3– has one unpaired
electron and was prepared by reducing the dianion, [Ni(mnt)2]2–, with potassium metal. The trianion and dianion
are members of the redox series [Ni(mnt)2]n− with n = 0, 1, 2, and 3.
The monoanion, [Ni(mnt)2]−, also has S = 1/2 and its rotational diffusion in diglyme was the
subject of previous ESR studies. This made possible the comparison
of the reorientational data for two different oxidation states of
the same planar complex in the same solvent. Differences were found;
isotropic rotational diffusion produced agreement between the trianion’s
experimental and calculated spectra, whereas the monoanion’s
simulations required axially symmetric reorientation with diffusion
about the long in-plane axis three times faster than that about the
two perpendicular axes. At a given temperature, the monoanion’s
reorientation rates about the long in-plane axis and two perpendicular
axes were faster than the trianion’s isotropic rate by factors
of ∼27 and ∼9, respectively. These differences suggest
that [Ni(mnt)2]− and [Ni(mnt)2]3– have different shapes and sizes in solution;
the monoanion is approximately a prolate ellipsoid, whereas the trianion
is larger and more spherical. [Ni(mnt)2]3– appears to be ion-paired, whereas in accord with results from other
techniques, [Ni(mnt)2]− is not.