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

Abstract

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.