Novel Organometallic Fullerene Complexes for Vehicular Hydrogen Storage

Theoretical studies have predicted that scandium can bind to the twelve five-membered rings in C₆₀. It is then possible to stabilize four dihydrogen ligands (H₂) on each Sc atom with a binding energy of ∼30 kJ/mol, ideal for vehicular hydrogen storage. The resulting C ₆₀[ScH₂(H₂)₄]₁₂ complex is predicted to be a minimum energy structure with ∼7.0 wt% reversible hydrogen capacity. However, wet chemical synthesis of the calculated η⁵-coordinated fullerene complex is unprecedented. The chemistry of C₆₀ is generally olefinic (i.e., η²-coordination, in which the metal is coordinated to two carbon atoms contributing two electrons to the bonding). Furthermore, stabilization of multiple dihydrogen ligands on a single transition metal has not been demonstrated. Recently we have probed new synthesis techniques in order to coordinate C₆₀ with either Fe, Sc, Cr, Co or Li. The new compounds were characterized with solid-state nuclear magnetic resonance, and structures have been proposed. All of the structures were found to have unique binding sites for hydrogen employing the technique of temperature programmed desorption. Furthermore, some of the structures were shown to have significant hydrogen capacities with volumetric measurements.