Anomalous Diamagnetic Susceptibility in 13-Atom Platinum Nanocluster Superatoms

We are used to being able to predict diamagnetic susceptibilities (D) to a good approximation in atomic increments since there is normally little dependence on the chemical environment. Surprisingly, we find from SQUID magnetization measurements that the (D) per Pt atom of zeolite-supported Pt-13 nanoclusters exceeds that of Pt2+ ions by a factor of 37-50. The observation verifies an earlier theoretical prediction. The phenomenon can be understood nearly quantitatively on the basis of a simple expression for diamagnetic susceptibility and the superatom nature of the 13-atom near-spherical cluster. The two main contributions come from ring currents in the delocalized hydride shell and from cluster molecular orbitals hosting the Pt5d and Pt6s electrons.