  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.
