Unusual Conformation of a Dinuclear Paddle Wheel Copper(II) Complex. Synthesis, Structural Characterization and EPR Studies

An
unusual and unique conformation of a paddle wheel type binuclear copper­(II)
complex containing acetate and acetamido ligands, {Cu2(μ2-O2CCH3)4}­(OCNH2CH3) (1), was obtained by solvothermal synthesis.
The structural characterization of this compound shows that the apical
(acetamido) ligands are disposed at a 62° dihedral angle, generating
a special conformation as a consequence of the synthetic method used.
This conformation has not been reported in other paddle wheel copper­(II)
tetraacetate compounds. Electron paramagnetic resonance (EPR) spectra
of powder samples of (1) were obtained at 9.5 and 33.8
GHz, while single crystal spectra were obtained at 33.8 GHz with a B0 applied in three orthogonal planes.
The fit of the single crystal experimental data allowed gave g∥ = 2.345 ± 0.003, and g⊥ = 2.057 ± 0.005. The angular variation of
the EPR line allows evaluation of the fine structure of (1), giving D = −0.337 ± 0.002 cm–1 and E = −0.005 ± 0.001
cm–1. The line width angular dependence, used together
with the Anderson model and Kubo–Tomita theory, permitted the
interdimer interaction to be evaluated as |J′|
= (0.051 ± 0.002) cm–1. Using the powder spectral
temperature dependence it was possible to evaluate the intradinuclear
exchange coupling constan J0 as −101
± 2 cm–1, which is considerably lower than
that reported for other analogous copper­(II) tetraacetate paddle wheel
compounds (CuII–PW), showing the remarkable effect
of the conformation of the terminal ligands on the magnetic interaction.