Silicon Containing Nine Atom Clusters from Liquid Ammonia Solution: Crystal Structures of the First Protonated Clusters [HSi₉]^3– and [H₂{Si/Ge}₉]^2–

Abstract

Experiments in liquid ammonia, originally aiming at reactions between Si containing Zintl clusters and transition metal complexes, lead to crystallization of several solvates of nineatomic cluster compounds.

Anionic Siliconoids from Zintl Phases: R3Si9− with Six and R2Si92− with Seven Unsubstituted Exposed Silicon Cluster Atoms (R=Si(tBu)2H)

“…A transfer of the extraction products from liquid ammonia to pyridine yielded the doubly‐protonated species H 2 Si 9 2− . A similar procedure allowed for the structural characterization of the iso‐valence‐electronic cluster with mixed tetrel elements H 2 Si 9− x Ge x 2− ( x= 4.1) . Both, HSi 9 3− and H 2 Si 9 2− , were fully characterized by 1 H and 29 Si NMR spectroscopy in solution.…”

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR, Raman, Mass Spectrometric, and Quantum Chemical Investigation

“…Regarding the extraction of nine-atomic clusters in K 12 Si 17 and K 12 Si 8 Ge 9 with liquid ammonia or py after subsequent transfer from liquid NH 3 solution, arecent report establishes the presence of protonated [HSi 9 ] 3À and [H 2 Si 9Àx Ge x ] 2À (x = 4.1) species by the single-crystal X-ray structure determination of [(K-18crown6) 3 (HSi 9 )]·2 NH 3 ·2 thf and [(K-18crown6) 2 [H 2 Si 4.9 Ge 4.1 ]·py. [22] As the mono-protonated species crystallizes from liquid ammonia solution and the diprotonated species after the subsequent transfer to py, [H 2 Si 9 ] 2À is assumed to be present in the extraction product here.T he Raman spectrum of 1 (Figure 2d)reveals one dominating vibration at 386 cm À1 ,w hich is indicative for [Si 9 ] 4À and [H 2 Si 9 ] 2À clusters as this value compares well to the calculated value of [Si 9 ] 4À and [H 2 Si 9 ] 2À at 395 cm À1 and 394 cm À1 ,r espectively ( Figure 2). 29 Si-MAS NMR investigation of solid 1 (Figure 3c (Figure 5a)a nd confirms also the presence of the doubly protonated species.A n addition of two protons at the [Si 9 ] 4À cluster units was also observed for [Cu(NHC Dipp )Si 9 ] 3À after its transfer from liquid ammonia to py,r esulting in the mass peak of {(NHC Dipp Cu)[H 2 Si 9 ]} À .…”

Crystal Structure of the Protonated Germanide Cluster [HGe9]3−

“…Here, [Ge 9 ] 4− can be considered as the base and [HGe 9 ] 3− as the formal conjugated acid. For the lighter and the heavier homologous elements of group 14, the formation of [HSi 9 ] 3− and [HSn 9 ] 3− has already been reported in the literature [15,32], as well as [H 2 Si 9 [14]. Thus, it seemed highly likely that pure [Ge 9 ] 4− clusters would also undergo similar protolytic reactions.…”

“…The Ge-H distance of 1.39(9) Å is slightly shorter than the values found in the literature (1.45(3) Å [57]). The proton is also located on a vertex germanium atom of the basal square plane, as it is supposed to be for [HSn 9 ] 3− [32], and found at [HSi 9 ] 3− [14,15].…”

“…This changed after the introduction of the chelating alkali metal ligand cryptand to these solutions by Corbett [4,5], when the isolation and structural characterization of solvate structures containing Zintl anions was facilitated. At present, for group 14 elements the representative homoatomic cluster anions identified in several solid state and solvate structures are [E 4 ] 4− (E = Si-Pb) [6][7][8][9], [E 5 ] 2− (E = Si-Pb) [10][11][12][13], [E 9 ] x− (x = 4; E = Si-Pb; x = 3, E = Si-Sn; x = 2 E = Si,Ge) [5,[14][15][16][17][18] and [E 10 ] 2− (E = Ge, Pb) [19,20]. For solvation experiments with germanium clusters, A 4 Ge 9 (A = K-Cs) [21,22] or A 12 Ge 17 (A = Na, K, K/Rb, Rb, Cs) [23,24] phases are used as starting materials, which contain the nine-atom germanide cluster or respectively [Ge 9 ] 4− /[Ge 4 ] 4− cage anions in a ratio of 1:2.…”