Tetrahedral [Tt(4)](4-) Zintl Anions Through Solution Chemistry: Syntheses and Crystal Structures of the Ammoniates Rb4Sn4 center dot 2NH(3), Cs4Sn4 center dot 2NH(3), and Rb4Pb4 center dot 2NH(3)

The crystalline isotypic solvates Rb4Sn4 center dot 2NH(3), Cs4Sn4 center dot 2NH(3), and Rb4Pb4 center dot 2NH(3) have been synthesized using the direct reduction of elemental tin or tetraphenyltin, respectively, with heavier alkali metals or the dissolution of the binary phase RbPb in liquid ammonia. These compounds contain the cluster ions [Sn-4](4-) or [Pb-4](4-) respectively This is the first time that [Tt(4)](4-) ions (Tt = tetrels) are detected as result of a Solution reaction. The accommodation of the ammonia molecules, which build up ion-dipole interactions to alkali metal cations, requires some modifications of the crystal structures compared to the binary phases RbSn, CsSn, and RbPb. The tetrahedral [Tt(4)](4-) anions have a slightly lower coordination by Rb+ or Cs+ cations and, furthermore, the intercluster distances show a remarkable increase.