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 η 3 - mode, the other where one is η 3 - and the other η 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.