Electron Paramagnetic Resonance Study of Copper–Ethylenediamine Complex Ion Intercalated in Bentonite

This work reports on studies of two-dimensional networks of Cu2+ ions, built by exchanging Na-bentonite with Cu2+ aqueous or with the bis­(ethylenediamine) complex, [Cu­(C2H4 (NH2))2]2+, at different concentrations of the paramagnetic center. Dilution of the magnetically active species is performed by the cointercalation of analogous diamagnetic zinc species, aqueous Zn2+, or complexed [Zn­(C2H4 (NH2))2]2+ ions, with ethylenediamine in excess. Materials were characterized by X-ray diffraction, Fourier transform infrared (FT-IR) and UV–visible spectroscopy, and continuous-wave electron paramagnetic resonance (EPR). X-ray diffraction measurements indicated that the interlaminar distance in the bentonite decreases with the increase of Zn concentration in the composites. The observation of a two-component Cu2+ EPR spectrum imply the coexistence of isolated Cu2+ with a well-resolved hyperfine structure and spin–spin exchanged Cu2+ dimers or clusters with an unresolved hyperfine structure. EPR spin Hamiltonian parameters of the isolated species in Cu/ethylenediamine intercalated samples are typical of axially distorted sites, six-coordinated with bis­(ethylenediamine) in the equatorial plane and with oxygen on the internal surfaces of the clay. Experimental facts indicate that the interaction between paramagnetic centers is mainly favored by two different phenomena: turbostratic disorder of clay sheets and segregation of the magnetic centers leading to interstratifications of layers.