Metallic Hydrides

Many of the elements in the d-block, and the lanthanide and actinide elements in the /-block, react with H2 and form metallic hydrides. How-
ever, the elements in the middle of the d-block do not form hydrides. The absence of hydrides in this part of the periodic table is· sometimes· called 
the hydrogen gap. 
Metallic hydrides are usually prepared by heating the metal with hydrogen under high pressure. (If heated to higher temperatures the hydrides decompose, and this may be used· as a convenient method of making very pure hydrogen.) 
These hydrides generally have properties similar to those of the parent metals: they are hard, have a metallic lustre, conduct electricity, and have 
magnetic properties. The hydrides are less dense than the parent metal, because the crystal lattice has expanded through the inclusion of hydrogen.

Reference _consince of inorganic chemistry
By JD Lee
Page number  252