X-RAY-DIFFRACTION AND ELECTRIC DICHROISM STUDIES ON THE ADSORPTION OF METAL-COMPLEXES BY A CLAY

The binding structures of enantiomeric and racemic [M(phen)3]2+ (M = Ru, Fe; phen = 1,10-phenanthroline) complexes with sodium montmorillonite were studied by means of X-ray diffraction and electric dichroism measurements. The electron density curves along the c axis of a clay layer were determined for the powder samples of clay-chelate adducts. At maximum adsorption, the enantiomeric and racemic chelates formed the single-molecular and double-molecular layers in the interlayer spaces, respectively. The reduced linear dichroisms for the two characteristic bands in their electronic absorption spectra (i.e. the metal-to-ligand charge-transfer band at 400-500 nm and the ligand excitation bands at 240-280 nm) were determined for the bound metal complexes in a colloidal state. The orientation of a bound complex was elucidated by comparing the observed reduced linear dichroism with the ones calculated for the possible bound state in the interlayer space of a clay. The chelate was bound to a clay with its 3-fold symmetry axis at an angle of 60-65-degrees with respect to the surface. No difference was observed for the orientations of the bound species between the racemic mixture and the pure enantiomer of the complex.