Drastic changes in electronic, magnetic, mechanical and bonding properties from Zr2CoH5 to Mg2CoH5

Despite similarities in formulae and local structures of Zr2CoH5 and Mg2CoH5, they are shown from ab initio calculations to present contrasted electronic, magnetic, mechanical and bonding properties due to the environment of cobalt with hydrogen characterized by negatively charged CoHx entities (x=4, 5 resp.) and to the chemical nature of Zr versus Mg. Zr2CoH5 is found more cohesive, harder and less ductile than Mg2CoH5. High density of states at the Fermi level arises from out-of-plane non-bonding Co-dz2 in Zr2CoH5 which is found as metallic ferromagnet in the ground state, in contrast with non-magnetic and insulating Mg2CoH5.