THEORETICAL STUDIES ON THE INTERACTIONS BETWEEN A METAL COMPLEX AND A CLAY

Abstract

Ab initio Hartree-Fock molecular orbital (MO) calculations are carried out for a system of linked [SiO₄] ^4- and [Al0₄] ^5-tetrahedra (denoted by a cluster). The system is regarded as a model of the tetrahedral sheet of a clay. The effective charges from the Mulliken population analyses are almost constant when the number of tetrahedra in a cluster increases from 1 to 6. The MO calculation is extended for the system of a point positive charge located over the surface of a cluster. The obtained potential curves of the point positive charge coincide well with the electrostatic potentials due to the effective charges on the atoms of the cluster. The binding energy of a metal complex ion, [M (phen) ₃] ²⁺ (phen=1, 10-phenanthroline), with a cluster, {[SiO₄] ^4-} ₉₇₁/{[Al0₄] ^5-}, is estimated in terms of the electrostatic and van der Waals energies for the atomic pairs. The orientation of the chelate at the minimum energy is compared with the recent experimental results for an adduct of the chelate with montmorillonite clay.