Tris(Acetylacetonato)Silicon(IV) Binding to Montmorillonite and Hydrolysis to Interlayer Silicic Acid

Charles G. Manos Jr.1, M. M. Mortland and Thomas J. Pinnavaia
Department of Crop and Soil Science, Michigan State University, East Lansing, Michigan 48824
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824
1 Present Address: Department of Agronomy, Cornell University, Ithaca, New York 14853.

Abstract: The reactions of the tris(acetylacetonato)silicone(IV) cation (Si(acac)3+) with Na+-, Mg2+-, and Co2+-exchange forms of hectorite and montmorillonite have been investigated to understand better the formation process of clays pillared by silicic acid. In acetone as the solvating medium, Si(acac)3+ binds to the Na+- and Mg2+-clays with the desorption of only a small fraction (∼5%) of the initial exchange cation, suggesting that the complex binds as the ion pair [Si(acac)3+][Cl]. With the Co2+-clays, however, the exchange cation is desorbed quantitatively, and Si(acac)3+ binding is accompanied by the formation of an acetone-solvated CoCl2 solution complex which helps to drive the ion-exchange reaction. Thus, Co2+-smectites react with Si(acac)3+ in acetone to produce homoionic Si(acac)3+ intercalates, whereas Na+- and Mg2+-smectites produce mixed-ion intercalates. The interlayer hydrolysis of Si(acac)3+ to silicic acid in the homoionic Si(acac)3+- and mixed-ion Na+/Si(acac)3+- and Mg2+/Si(acac)3+-exchange forms of montmorillonite films is diffusion controlled. In water as the solvating medium, the reaction of Si(acac)3+ with Mg2+- or Co2+-montmorillonite results in the desorption of the exchange cations on a time scale which is comparable to that observed for the solution hydrolysis of Si(acac)3+. Thus, the precipitation of silicic acid from aqueous solution competes strongly with the formation of interlayer silicic acid. With aqueous Na+-montmorillonite dispersions, however, a significant fraction of the exchange cations desorbed rapidly upon Si(acac)3+ binding, and the formation of interlayer silicic acid is favored over the precipitation of Si(OH)4.

Key Words: Hydrolysis • Montmorillonite • Pillared interlayer complex • Si(acac)3+ • Silicic acid

Clays and Clay Minerals; April 1984 v. 32; no. 2; p. 93-98; DOI: 10.1346/CCMN.1984.0320202
© 1984, The Clay Minerals Society
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