On the Stability of Sodium-Tin Zintl Ions in Gas phase experiments

A synergistic effort combining negative ion photoelectron spectroscopy of Na$_{n}$Sn$_{m}^{-}$ clusters along with the first principles electronic structure studies has been used to demonstrate that Zintl ions found in solutions also exist as stable species in free clusters. The theoretical investigations are carried out within a gradient corrected density functional approach. Our studies on Na$_{n}$Sn$_{4}^{-}$ clusters where n=0-4 and NaSn$_{m}^{-}$ clusters where m=4-7 show that Na$_{3}$Sn$_{4}^{-}$ is a very stable cluster marked by a distorted tetrahedral tin core and can be regarded as (Na+)$_{4}$(Sn$_{4})^{-4}$ gas phase analogue of the Na:Sn tetrahedral Zintl phase. In addition, the NaSn$_{5}^{-}$ cluster is shown to be the most abundant species in the mass spectrum in the NaSn$_{m}^{-}$ series and its stability can be reconciled with Sn$_{5}^{2-}$ Zintl ions. The existence of stable Zintl ions in the gas phase can provide an alternate approach to look for possible Zintl phases.