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

A new Zintl cluster, [(Ni@Sn-9)In(Ni@Sn-9)](5-), has been isolated in two distinct isomeric forms, one where both Ni@Sn-9 units are coordinated to the bridging In atom in an eta(3)- mode, the other where one is eta(3)- and the other eta(4)-. 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@Sn-9)In(Ni@Sn-9)](5-) with [(Ni@Ge-9)Ni(Ni@Ge-9)](4-), which has four fewer valence electrons, sheds some light on possible mechanisms that lead to the fusion of cluster fragments.