Using first-principles calculations,we predict that a single C2H4 or C5H5 molecule can form a stable complex with two rare earth metals such as La,Eu,and Ho.The La2C2H4 complex then absorbs up to sixteen hydrogen molecules,reaching a gravimetric storage capacity of 9.5wt％ by adding a rare-earth metal atom,The results show that Eu-4f electrons have little impact on the hydrogen adsorption.The nature of bonding between Eu and H2 is due to the hybridization of Eu-5d with the H-1s orbital.