Thermodynamical stability of complex transition metal hydrides M ₂FeH₆

The thermodynamical stability of complex transition metal hydrides M ₂FeH₆ is investigated by first-principles density-functional calculations. In addition to the reported alkaline-earth compounds (M = Mg, Ca, and Sr), hypothetical Mn₂FeH₆ and Zn₂FeH₆ are considered to examine chemical trends. Some double-cation systems, (MM′)FeH₆, are also taken into consideration. A good correlation between the standard heats of formation of these compounds and the electronegativities of cation elements can be found as done in borohydrides [Nakamori et al., Phys. Rev. B2006, 74, 045126]. A cation electronegativity is found to be a good indicator to estimate the stability of Fe-based complex transition metal hydrides.