Interstitial compounds are those which are formed when smallatoms like H, C or N are trapped inside the crystal lattices of metals. Theyare usually non stoichiometric and are neither typically ionic nor covalent,for example, TiC,Mn4N,Fe3H,VH0.56 and TiH1.7, etc.
These do not correspond to any normal oxidation state of the metal.Because of the nature of their composition, these compounds arereferred to as interstitial compounds.The principal physical and chemicalcharacteristics of thesecompounds are as follows :
(i) They have high melting points, higher than those of pure metals.
(ii) They are very hard, some borides approach diamond in hardness.
(iii) They retain metallic conductivity
(iv) They are chemically inert.