What are metallic or interstitial hydrides? How do they differ from molecular hydrides?

(N/A) Metallic or interstitial hydrides are formed by many $d$-block and $f$-block metals. These hydrides are conductors of heat and electricity.
Except for saline hydrides,almost all hydrides are primarily non-stoichiometric and are deficient in $H_2$.
For example,$LaH_{2.87}, YbH_{2.55}, TiH_{1.5-1.8}, VH_{0.56}, NiH_{0.6-0.7}, PdH_{0.6-0.8}$,etc. The law of constant composition does not apply to these hydrides.

Molecular Hydrides	Metallic Hydrides
These are primarily formed by $p$-block elements and some $s$-block elements $(Be, Mg)$.	These are primarily formed by elements of groups $3, 4, 5, 10, 11, 12$ and $f$-block elements.
They form volatile compounds with low melting and boiling points.	They form hard compounds that exhibit some metallic character.
They are insulators (non-conductors) of electricity.	They are conductors of electricity.