The intercalation of Co2+, [Co(NH3)(6)](3+), and [Co(NH3)(5)CL](2+) ions into layered manganese oxide (birnessite) was studied by chemical, XRD, SEM, IR. and DTA-TG analyses. The intercalation reaction progressed by a 2:1 or 3:1 ion-exchange mechanism depending on the valence of the starting ions. The oxidation state of cobalt did not change with the intercalation reaction. The intercalation of [Co(NH3)(6)](3+) ions resulted in an increase of basal spacing from 0.716 to 0.956 nm, giving a layered structure material consisting mainly of platelike particles. The chemical analysis results showed that the structure of [Co(NH3)(6)](3+) ions was maintained in the interlayer. On the other hand, an H2O/NH3 ligand exchange reaction progressed for the intercalation of [Co(NH3)(5)Cl](2+) ions, resulting in an increase in the basal spacing from 0.716 to 0.956 nm. (C) 2003 Elsevier Inc. All rights reserved.