Toward an Understanding of Ligand Selectivity in Nanocluster Synthesis

We performed scalar relativistic density functional theory (DFT) calculations using the projector augmented wave scheme (PAW) to examine the reactivity and selectivity of diphosphine ligands L M, with the formula PH 2 (CH 2 ) M PH 2 (spacer M = 3, 5), toward small-sized cationic Au n ( n = 7–11) nanoclusters. By isolating the ligand-induced contribution to the stability condition, we show that such interaction selectively stabilizes the cationic Au 11 cluster. Furthermore, we find that L 5 with the longer spacer is more capable than L 3 of relieving the strain imposed on the spacer by bidentate binding to gold clusters, which have relatively small Au–Au bond lengths. Thus L 5 can interact effectively with gold clusters of various sizes, but L 3 can do so only with a selected few. This result demonstrates the size-selecting power of L 3 toward small gold clusters such as Au 11 3+ . To further test the validity of our results we have extended the calculation to a larger cluster, Au 13, and also considered the case of a ligand with a larger spacer, M = 10, interacting with a small cluster (Au 3 ). We find that, for Au 13 (L 3 ) 6 5+, the strain induced by the stiff L 3 spacer causes the gold cluster to disintegrate. We also predict a single-end binding for the interaction of L 3 with the gold trimer: one end of the diphosphine is detached from the trimer. Finally, for an ideal, highly selective ligand, we propose a two-body ligand system, in which one part of the ideal ligand provides high reactivity toward the broad range of gold clusters and the other part provides control over the reactivity. The controllable competition between the two components of an ideal, highly selective ligand system will produce a desirable selectivity for the generation of monodisperse nanoclusters of interest through tailoring process.