The interplay between d cationic levels and sp anionic band may result in a partial depopulation of the latter. The holes that are created may associate and lead to anionic catenation with a possible cut-off of the top of the sp band. In any case electrons transferred through an intercalation process will be accepted on levels which are largely anionic in character. Holes at the top of sp bands are at the origin of a nice soft chemistry of the redox type. Their neutralization by electrons allows to stabilize unusual structural types.