MONTE-CARLO SIMULATIONS FOR THE INTERACTIONS OF METAL-COMPLEXES WITH THE SILICATE SHEETS OF A CLAY - COMPARISON OF BINDING STATES BETWEEN TRIS(1,10-PHENANTHROLINE)METAL(II) AND TRIS(2,2'-BIPYRIDYL)METAL(II) CHELATES

Monte Carlo simulations are used to compare the binding states of tris(1,10-phenanthroline)metal(II) ([M(phen)3]2+) and tris(2,2'-bipyridyl)metal(II) ([M(bpy)3]2+) bound to a clay. A pair of [M(phen)3]2+ or [M(bpy)3]2+ complexes is placed on the model surface of a silicate sheet. The surface is composed of linked [SiO4]4- and [AlO4]5- tetrahedra. The binding energy is obtained as the sum of the interaction energies of the metal complexes with the sheet and the intermolecular energy between the metal complexes. The stable binding state is examined in terms of the free energy at 300 K as a function of the intermolecular distance, r(M-M). For [M(phen)3]2+, a racemic pair has the minimum free energy at r(M-M) = 9.2 angstrom, and an enantiomeric pair has the minimum free energy at r(M-M) = 13.4 angstrom. The mean binding energy (E) for the racemic pair is 1.5 kJ/mol lower than that for the enantiomeric pair. The results indicate that the racemic mixture forms a more compact and stable pair than does the pure enantiomer. For [M(bpy)3]2+, racemic and enantiomeric pairs have the minimum binding free energy at nearly the same values of r(M-M): r(M-M) = 9.3 angstrom for a racemic pair and 9.5 angstrom for an enantiomeric pair. E is 25.3 kJ/mol lower for the racemic pair than for the enantiomeric pair. Thus a pair of the metal complexes form a dimer with similar compactness irrespective of the chirality of the complexes. These results are compared with experimental observations of the chirality effects on the adsorption behaviors of these metal complexes by a clay.