Structural isomerism in the [(Ni@Sn9)In(Ni@Sn9)]5− Zintl ion

Abstract

A new Zintl cluster, [(Ni@Sn₉)In(Ni@Sn₉)]⁵⁻, has been isolated in two distinct isomeric forms, one where both Ni@Sn₉ units are coordinated to the bridging In atom in an η³- mode, the other where one is η³- and the other η⁴-. Density functional theory indicates that the energetic separation between these two structures is minimal, suggesting that crystal packing plays a decisive role in the structural chemistry. A comparison of the electronic structure of [(Ni@Sn₉)In(Ni@Sn₉)]⁵⁻ with [(Ni@Ge₉)Ni(Ni@Ge₉)]⁴⁻, which has four fewer valence electrons, sheds some light on possible mechanisms that lead to the fusion of cluster fragments.