Intermediate hydrides

Not all hydrides can be placed in the above categories, e.g. those of Pd, Cu, lanthanoids and actinoids. Palladium reversibly absorbs large amounts of H₂ or D₂ (but no other gases, a fact that is of great importance in the separation of H₂ from gaseous mixtures). The absorbed hydrogen has a high mobility, but the form in which it is present has not been established, although the limiting composition is known to be ≈PdH_0.7.