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

A new Zintl cluster, [(Ni@Sn9)In(Ni@Sn9)]5–, has been isolated in two distinct isomer forms, one where both Ni@Sn9 units are coordinated to the bridging In atom in an eta3 mode, the other where one is eta3 and the other eta4. 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.