Solvation of exchangeable copper(2+) cations by primary alcohols in montmorillonite clay studied by electron spin resonance and electron spin echo modulation spectroscopies

Abstract

A montmorillonite clay (STx-1), with Mg/sup 2 +/ as the major exchangeable cation and Cu/sup 2 +/ exchanged into 5% of the Mg/sup 2 +/ sites, is used to study the interaction between the exchangeable cations and adsorbed primary alcohols, methanol, ethanol, and 1-propanol, in the clay interlayer region. Electron spin resonance (ESR) shows that, on saturation of the clay with methanol, a freely rotating Cu/sup 2 +/ center is formed in the clay interlayer. Electron spin echo modulation (ESEM) spectroscopy indicates that the center is a four-coordinate Cu/sup 2 +/ solvate, in which the methanol ligands are in a square-planar configuration. On adsorption of ethanol into the interlayer region, a rotationally restricted Cu/sup 2 +/ center is detected. ESEM again indicates a four-coordinate, square-planar solvate, and ESR of oriented clay films reveals that the major symmetry axis of the ethanol-solvated Cu/sup 2 +/ center is perpendicular to the plane of the clay lattice. Similar ESP data are reported for 1-propanol-saturated montmorillonite, and a four-coordinate, square-planar Cu/sup 2 +/ solvate, similar to that described for ethanol, is proposed.