What are interstitial compounds? Why are such compounds well known for transition metals?
Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals. They are usually non-stoichiometric and are neither typically ionic nor covalent. Examples include TiC, Mn₄N, Fe₃H, VH₀.₅₆ and TiH₁.₇.
Such compounds are well known for transition metals because transition elements exhibit a tendency for the formation of interstitial compounds. The formulas of these compounds do not correspond to any normal oxidation state of the metal. Due to the nature of their composition, these compounds are referred to as interstitial compounds.
Explanation
The textbook defines interstitial compounds in section 4.3.13 as compounds formed when small atoms (H, C, N) get trapped in metal crystal lattices. They are non-stoichiometric and neither ionic nor covalent. Transition metals are known for forming these compounds as stated in the text: 'they exhibit paramagnetic behaviour, catalytic properties and tendency for the formation of coloured ions, interstitial compounds and complexes.'