Binding motifs for lanthanide hydrides: A combined experimental and theoretical study of the MH _x(H ₂) _y species (M = La-Gd; x = 1-4; y = 0-6)

The results of a combined spectroscopic and computational study of lanthanide hydrides with the general formula MH _x(H ₂) _y, where M = La, Ce, Pr, Nd, Sm, Eu, and Gd, x = 1-4, and y = 0-6 are reported. To understand the nature of the dihydrogen complexes formed with lanthanide metal hydride molecules, we have first identified the binary MH _x species formed in the ablation/deposition process and then analyzed the dihydrogen supercomplexes, MH _x(H ₂) _y. Our investigation shows that the trihydrides bind dihydrogen more weakly than the dihydrides and that the interaction between the central lanthanide and the H ₂ molecules occurs via a 6s electron transfer from the lanthanide to the H ₂ molecules. Evidence is also presented for the SmH and EuH diatomic molecules and the tetrahydride anions in solid hydrogen.