A Stannyl-Decorated Zintl Ion [Ge18Pd3(Sn′Pr3)6]2-: Twinned Icosahedron with a Common Pd3-Face or 18-Vertex Hypho-Deltahedron with a Pd3-Triangle Inside

We report the synthesis and character ization of the title anion which has a germanium/palladium cluster core of [Ge18Pd3] and six tri-isopropyl tin substituents. Its two Ge-9-halves are the first examples of germanium deltahedra with three nonsilyl substituents, triisopropyl tin in this case. The new cluster is made by a reaction of an acetonitrile suspension of K4Ge9 with (Pr3SnCl)-Pr-i that generates primarily tristannylated 9-atom clusters [Ge-9{(SnPr3)-Pr-i}(3)](-), followed by addition of Pd-(PPh3)(4) to the reaction mixture. It was structurally characterized by single-crystal X-ray diffraction in [K-(222crypt)](2)[(GePd3)-Pd-i{(SnPr3)-Pr-i}(6)].(Pr2O)-Pr-i and was also confirmed in solution by ESI-MS and NMR The new anion can be viewed both as a dimer of face-fused icosahedra (twinned icosahedron) with a common Pd3-face, i.e., [('Pr3Sn)(3)Ge9Pd3Ge9((SnPr3)-Pr-i)(3)](2-) that resembles but is not isoelectronic with the known borane version B(21)H18(-) or as a large hypho-deltahedron of 18 Ge-atoms with a triangle of Pd-3 inside, i.e., [Pd-3@Ge-18((SnPr3)-Pr-i)(6)](2-). DFT calculations show a very large HOMO LUMO gap of 2.42 eV.