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

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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 mea- surements of non-oriented powder samples: 14.3 ~, for (Co(en)3) 3+ montmorillonite, 16.5 ~ for (Co(diNOsar)) 3+ montmorillonite, and 16.9 A 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 per- pendicular to the surface. The conclusion is consistent with the angular dependence of the infrared absorption spectrum of the film of the adduct.