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) (<b>1</b>), 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 (<b>1</b>) were obtained at 9.5 and 33.8 GHz, while single crystal spectra were obtained at 33.8 GHz with a <i><b>B</b></i>₀ applied in three orthogonal planes. The fit of the single crystal experimental data allowed gave <i>g</i>_∥ = 2.345 ± 0.003, and <i>g</i>_⊥ = 2.057 ± 0.005. The angular variation of the EPR line allows evaluation of the fine structure of (<b>1</b>), giving <i>D</i> = −0.337 ± 0.002 cm^–1 and <i>E</i> = −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 |<i>J</i>′| = (0.051 ± 0.002) cm^–1. Using the powder spectral temperature dependence it was possible to evaluate the intradinuclear exchange coupling constan <i>J</i>₀ as −101 ± 2 cm^–1, which is considerably lower than that reported for other analogous copper­(II) tetraacetate paddle wheel compounds (Cu^II–PW), showing the remarkable effect of the conformation of the terminal ligands on the magnetic interaction