New topochemical reactions of layered inorganic materials

Lamellar inorganic solids have interesting physical properties related to anisotropic transport of electrons and ions, host-guest chemistry, magnetism, and catalysis. Because these solids are held together in the stacking direction by relatively weak bonds, they are subject to intercalation and exfoliation reactions, as well as low-temperature topochemical reactions that convert one structure type into another. We have recently found that intercalation of cationic polymers into anionic layered hosts can invert the charge on the sheets, making the galleries hosts for anionic molecular guests and nanoparticles. Topochemical condensation reactions can be used to convert layered solids into three-dimensionally bonded materials with unusual crystal textures, magnetic, and electronic transport properties. The anisotropic bonding in diamagnetic layered compounds also leads to anisotropy in their magnetic susceptibility, such that they tend to align in strong magnetic fields with one of their in-plane axes parallel to the field direction. We are now studying this effect as a means of preparing oriented particle membranes of proton-conducting platelets, exfoliated sheets, and nanoscrolls for intermediate temperature fuel cells.