Polymeric hydroxy-chromium cations are prepared from chromium nitrate solutions by addition of NaOH to yield ОН/Cr ratios 0, 0.5, 1.0, 1.5, 2.0. Hydroxy-chromium montmorillonites are obtained by ion-exchange reactions, and the compositions of the interlayer hydroxy complexes are derived from chemical analyses of the products. Even without addition of NaOH to the chromium nitrate solution, the exchanged Cr ions are partially hydrolyzed within the clay and have a composition near [Cr(OH)(H2O)5]2+. As the ratio ОН/Cr in the nitrate solution is increased, polymeric cations are formed in the clay with increasing numbers of Cr ions and with a higher ratio of ОН/Cr than in the external solution. With increasing polymerization of the interlayer material, the basal spacings of the montmorillonites increase to about 16.8А and are stable to about 200°C. Surface areas of the 200°C heated montmorillonites, determined by N2 absorption, increase linearly with the basal spacing up to about 280 m2/g when the spacing is near 16.8А.

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