The Structure of [HSi₉]³⁻ in the Solid State and Its Unexpected Highly Dynamic Behavior in Solution

Abstract

We report on the first unambiguous detection of the elusive [HSi ] anion in solutions of liquid ammonia by various Si and H NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the Si and H resonances together with CEST and a partially reduced H, Si coupling constant indicate the presence of a highly dynamic Si entity and a Si-H moiety with slow proton hopping. Theoretical calculations corroborate both reorganization of Si on the picosecond timescale via low vibrational modes and proton hopping. In addition, in a single-crystal X-ray study of (K(DB[18]crown-6))(K([2.2.2]crypt)) [HSi ]⋅8.5 NH , the H atom was unequivocally localized at one vertex of the basal square of the monocapped square-antiprismatic cluster. Thus experimental studies and theoretical considerations provide unprecedented insight into both the structure and the dynamic behavior of these cluster anions, which hitherto had been considered to be rigid.

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

“…The 29 Si NMR resonance at 18.00 ppm is attributed to the three equivalent Si( t Bu) 2 H groups, whereas the strongly high‐field shifted signals at −175.16 and −358.81 ppm arise from the three substituted and six unsubstituted Si vertex atoms in the Si 9 polyhedron, respectively. The experimental 29 Si NMR signal γ (−358.81 ppm) of the unsubstituted vertex atoms shows a stronger upfield shift, as usually observed for prominent siliconoid species, and is comparable to the signals for the protonated Si 9 cluster species HSi 9 3− (unsubstituted vertex atoms: −359 ppm) and to the experimental and calculated 29 Si NMR average values for H 2 Si 9 2− (exp. : −346 ppm; calcd: −348 ppm).…”

“…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. The formation of well‐defined solutions that contain nine‐atom silicon clusters after activation with liquid ammonia finally paved the way for further conversions of these clusters in solution with appropriate reactants.…”

Atomically Precise Expansion of Unsaturated Silicon Clusters

“…[11] While solvated Zintl ions-charged, polyhedral clustersof germanium and tin can be used as well-defined precursors for the synthesis of partially substituted molecular clusters, [12] the strongly reducing silicon congeners have only been employed as ligands towards af ew redox-stable transitionmetal fragments, [13] and were only very recently protonated to the partially hydrogen-substituted clusters [HSi 9 ] 3À and [H 2 Si 9 ] 2À . [14] Therefore,s iliconoids are typically accessed by Scheme 1. Selected saturated and unsaturateds ilicon clusters.…”

Erweiterung ungesättigter Siliciumcluster mit atomarer Genauigkeit

“…[13] Erst kürzlich wurde über die Protonierung zu den teilweise wasserstoffsubstituierten Clustern [HSi 9 ] 3À und [H 2 Si 9 ] 2À berichtet. [14] Deshalb werden Silicoide typischerweise durch reduktive Spaltung geeigneter Abgangsgruppen aus klassischen, gesättigten Vorläufern erhalten. Dieser Ansatz wurde zunächst durch die Herstellung von gesättigten polyedrischen Siliciumclustern wie Hexasilaprisman R 6 Si 6 5a,b [15] und Tetrasilatetrahedran R 4 Si 4 6a,b [16] [17] das zuvor aus einem anderen R 3 Si 4 -Vorläufer durch Reduktion synthetisiert worden war.…”

“…Si-NMR-chemischen Verschiebungen des B3LYP-optimierten Modells Tip 5 Si 7 (Li)thf3 [14 Tip ·Li + (thf)3 ]e rhalten, welche die experimentellen Daten von 14·Li + (thf)3 (Tabelle 1) gut reproduzieren. Kristalle von 14 wurde aus Pentan in 42 %iger Ausbeute erhalten.…”