Investigation of structural changes in Ni-19 and Ni-23 induced by adsorption of hydrogen/deuterium and ammonia

Two-reagent reactions of Ni-19 and Ni-23 with hydrogen/deuterium and ammoni a are studied to probe adsorbate-induced cluster structural changes. H/D an d NH3 bind to the clusters noncompetitively, i.e., to different sites, so s imultaneous saturation by the two reagents can be achieved. It is found tha t HID adsorption causes a change in Ni-19 from the double icosahedral struc ture to a face-centered cubic (fee) or hexagonal close-packed (hcp) one, bu t that subsequent saturation with NH3 Converts the cluster back to the doub le icosahedron. No such structural changes are seen for the triple icosahed ral Ni-23. The results for Ni-19 are interpreted in terms of the electron w ithdrawing or donating character of the ligands and the consequent effect o n the extent of d-orbital bonding in the cluster. Possible configurations o f the H/D atom binding sites on the icosahedral Ni-19 and Ni-23 clusters an d on the fcc/hcp Ni-19 cluster are presented. (C) 2001 American Institute o f Physics.