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The existence of [μ‐HSi4]3− in liquid ammonia solutions is confirmed by 1H and 29Si NMR experiments. Both NMR and quantum chemical calculations reveal that the H atom bridges two Si atoms of the [Si4]4− cluster, contrary to the expectation that it is located at one vertex Si of the tetrahedron. The calculations also indicate that in the formation of [μ‐HSi4]3−, protonation is driven by a high charge density and an increase of electron delocalization compared to [Si4]4−. Additionally, [Si5]2− was detected for the first time and characterized by NMR. Calculations show that it is resistant to protonation, owing to a strong charge delocalization, which is significantly reduced upon protonation. Thus, our methods reveal three silicides in liquid ammonia: unprotonated [Si5]2−, terminally protonated [HSi9]3−, and bridge‐protonated [μ‐HSi4]3−. The protonation trend can be roughly predicted by the difference in charge delocalization between the parent compound and the product, which can be finely tuned by the presence of counter ions in solution. [ABSTRACT FROM AUTHOR]

We report on the asymmetric occupation of a 12‐vertex cluster centered by a single metal atom. Three salts of related intermetalloid cluster anions, [Co@Sn6Sb6]3− (1), [Co2@Sn5Sb7]3− (2), and [Ni2@Sn7Sb5]3− (3) were synthesized, which have pseudo‐C4v‐symmetric or pseudo‐D4h‐symmetric 12‐vertex Sn/Sb shells and interstitial Co− ions or Ni atoms. Anion 1 is a very unusual single‐metal‐"centered" 12‐atom cluster, with the inner atom being clearly offset from the cluster center for energetic reasons. Quantum chemistry served to assign atom types to the atomic positions and relative stabilities of this cluster type. The studies indicate that the structures are strictly controlled by the total valence electron count—which is particularly variable in ternary intermetalloid cluster anions. Preliminary 119Sn NMR studies in solution, supported by quantum‐chemical calculations of the shifts, illustrate the complexity regarding Sn:Sb distributions of such ternary systems. Asymmetric occupation of a 12‐vertex cage was found in the new ternary intermetalloid cluster [Co@Sn6Sb6]3− (see picture). According to DFT calculations, the observed structure represents the global minimum for the given composition. Beside this cluster, a related one was identified with two interstitial cobalt atoms, [Co2@Sn5Sb7]3−, as a minor component in the crystal structure, which was also confirmed by ESI mass spectrometry of a corresponding solution. [ABSTRACT FROM AUTHOR]