Two kinds of metal complexes, an achiral metal complex, [Fe(terpy)](2+) (terpy = 2,2',2"-terpyridyl), and a chiral metal complex, Delta-[Ni(phen)(3)](2+) (phen = 1,10-phenanthroline), were coadsorbed by colloidally dispersed sodium saponite clay. Interaction between these molecules on a clay surface was investigated by electric dichroism and circular dichroism measurements. The molecular orientation of an adsorbed [Fe(terpy)](2+) ion was determined in the absence or presence of Delta-[Ni(phen)(3)](2+) by electric dichroism measurements. The angle of the C-2 axis of [Fe(terpy)](2+) with respect to a clay surface changed from 35.4degrees to 44.4degrees when the complex was coadsorbed with Delta-[Ni(phen)3](2+). The circular dichroism spectrum of a clay dispersion containing [Fe(terpy)]Cl-2 and Delta-[Ni(phen)(3)]Cl-2 was measured in the wavelength region of 350-600 nm. Delta-[Ni(phen)(3)](2+) had no electronic absorption in this region. Circular dichroism due to adsorbed [Fe(terpy)](2+) appeared when Delta-[Ni(phen)(3)]Cl-2 was added to the ratio of [Fe(terpy)]Cl-2/Delta-[Ni(phen)(3)]Cl-2 from 1:1 to 1:3. The results were compared with the prediction by Kirkwood-Tinoco theory, in which circular dichroism is assumed to be induced by dipolar interaction with a chiral molecule.