ADSORPTION AND SPECTROSCOPIC STUDIES ON THE INTERACTIONS OF COBALT(III) CHELATES WITH CLAYS

The interactions of the following three kinds of racemic and enantiome ric cobalt(III) chelates with montmorillonite and saponite are studied : [Co(en)3]3+ (en = ethylenediamine), [Co(diNOsar)]3+ (diNOsar = ,19-h exaazabicyclo[6,6,61-eicosane)cobalt(III))and [Co(diAMsar)]3+ (diAMsar = 6,19-hexaazabicyclo-[6,6,6]eicosane)-cobalt(III)). At neutral pH, t hese complexes are adsorbed as a trivalent cation up to 90%-100% of th e cation exchange capacity of a clay. No difference is observed in the maximum adsorption amount between the racemic and enantiomeric isomer s. The basal spacings of the clay-chelate adducts are determined by th e X-ray diffraction measurements of non-oriented powder samples: 14.3 angstrom for [Co(en)3]3+ montmorillonite, 16.5 angstrom for [Co(diNOsa r)]3+ montmorillonite, and 16.9 angstrom for [Co(diAMsar)]3+ montmoril lonite. The results imply that the chelates form a monolayer in the in terlayer space. From the one-dimensional Fourier analyses of the diffr action pattern of [Co(diNOsar)]3+ montmorillonite, the chelate is conc luded to be adsorbed with its three-fold symmetry axis in parallel wit h the layer surface. This is in contrast with the previous results of (Ru(phen)3]2+ and [Ru(bpy)3]2+, which are adsorbed with their three-fo ld symmetry axes perpendicular to the surface. The conclusion is consi stent with the angular dependence of the infrared absorption spectrum of the film of the adduct.