Two series of monoionic (M) kaolinites (M = H+, Ca2+, Cu2+ Zn2+, Al3+ and Fe3+) were prepared from a natural Brazilian clay (Sao Simao clay, SP): series A, dried under vacuum at 25 degrees C, and series B, dried under vacuum at 25 degrees C. The natural clay was characterized by elemental analysis, cation exchange capacity, X-ray diffractometry, differential thermal analysis, and surface area measurements (BET). The interactions of M,M-dimethylacetamide and pyridine with these (M) kaolinites were studied by adsorption isotherms, titration calorimetry, and infrared spectroscopy (for pyridine only). The results indicated a coordinative interaction between M,M-dimethylacetamide and (M) kaolinites. For the interactions between pyridine and (M) kaolinites, the formation of hydrogen bonds (M = Al3+, Fe3+), hydrogen and coordinative bonds (M = Cu2+, Zn2+), and ionic pairs (M = H+, Ca2+) was observed. For the pyridine-(Cu) kaolinite system, a substitution of water coordinated to Cu2+ by pyridine was established. (C) 1996 Academic Press, Inc.177118