Exploring the Potential Energy Surface of Trimetallic Deltahedral Zintl Ions: Lowest-Energy [Sn6Ge2Bi]3- and [(Sn6Ge2Bi)2]4- Structures.

The synthesis and structural characterization of the dimer [(Sn6Ge2Bi)2]4- raise the possibility of obtaining a broad variety of analogous compounds with different Sn/Ge/Bi proportions. Several combinations of nine atoms have been detected by electrospray mass spectrometry as potential assembly units. However, [(Sn6Ge2Bi)2]4- remains as the unique experimentally characterized species in this series. This fact has motivated us to explore its potential energy surface, as well as its monomers' [Sn6Ge2Bi]3-/2-, in an effort to gain insight into the factors that might be privileging the experimental viability of this species. Our results show that the lowest-energy [Sn6Ge2Bi]3- structure remains in its oxidized product [Sn6Ge2Bi]2-, which corresponds to that identified in the dimer [(Sn6Ge2Bi)2]4-. Additionally, local minima, very close in energy to the lowest-energy monomer, are chiral mixtures that dimerize into diverse structures with a probable energetic cost, making them noncompetitive isomers. Finally, the global minimum of the dimer [(Sn6Ge2Bi)2]4- presents the most stable monomers as assembly units. These results show the importance of considering the simultaneity of all of these conditions for the viability of these types of compounds.