  Hydrogen trapping ability of various metal - ethylene complexes has been studied at the B3LYP and MP2 level of theory using the 6-311+G(d,p) basis set. Different global and local reactivity descriptors and the associated electronic structure principles provide important insights into the associated interactions. There exist two distinct classes of bonding patterns, viz., a Kubas-type interaction between the metal and the H2 molecule behaving as a {\eta}2-ligand and an electrostatic interaction between the metal and the atomic hydrogens. 
Analyzing the Efficiency of Mn-(C2H4) (M = Sc, Ti, Fe, Ni; n = 1, 2)   Complexes as Effective Hydrogen Storage Materials