Adsorption and Spectroscopic Studies on the Interactions of Cobalt(III) Chelates with Clays

Abstract

Abstract The interactions of the following three kinds of racemic and enantiomeric cobalt(III) chelates with montmorillonite and saponite are studied: [Co(en) 3 ] 3+ (en = ethylenediamine), [Co(diNOsar)] 3+ (diNOsar = (1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo[6,6,6]-eicosane)cobalt(III))and [Co(diAMsar)] 3+ (diAMsar = (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo-[6,6,6]eicosane)-cobalt(III)). At neutral pH, these complexes are adsorbed as a trivalent cation up to 90%–100% of the cation exchange capacity of a clay. No difference is observed in the maximum adsorption amount between the racemic and enantiomeric isomers. The basal spacings of the clay-chelate adducts are determined by the X-ray diffraction measurements of non-oriented powder samples: 14.3 Å for [Co(en) 3 ] 3+ montmorillonite, 16.5 Å for [Co(diNOsar)] 3+ montmorillonite, and 16.9 Å for [Co(diAMsar)] 3+ montmorillonite. The results imply that the chelates form a monolayer in the interlayer space. From the one-dimensional Fourier analyses of the diffraction pattern of [Co(diNOsar)] 3+ montmorillonite, the chelate is concluded to be adsorbed with its three-fold symmetry axis in parallel with 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-fold symmetry axes perpendicular to the surface. The conclusion is consistent with the angular dependence of the infrared absorption spectrum of the film of the adduct.