On reversible bonding of hydrogen molecules on platinum clusters.

The local reactivity of hydrogenated platinum clusters (Pt clusters) has been studied using the regional density functional theory method. We observed that antibond orbitals constitute the preferable binding site for hydrogen molecules H(2). Those sites are characterized by lowered electronic chemical potential and strong directionality and exhibit electrophilic nature. The platinum-dihydrogen (Pt-H(2)) sigma complexes were formed only by occupation of the lowest electronic chemical potential sites associated with Pt-H antibonds (sigma(PtH) ( *)) in saturated platinum clusters. The formation of sigma complexes caused mutual stabilization with the trans Pt-H bond. Such activated H(2) molecules on Pt clusters in a sense resemble heme-oxygen (heme-O(2)) complex with interaction strength greater than physisorption or hydrogen bonding but below chemisorption strength.