Metallderivate von Molekülverbindungen. II. Darstellung und Struktur des β‐Kaliumsilanids

Abstract

Kaliumsilanid kristallisiert bei −5°C aus 1,2‐Dimethoxyethan/n‐Pentan in einer bisher unbekannten Tieftemperatur‐Modifikation {β‐Form: orthorhombisch, Pnma, Z = 4; a = 880,0(2), b = 541,6(1), c = 682,3(1) pm bei −110 ± 3°C}. Nach den Ergebnissen der Röntgenstrukturanalyse (R = 0,032) baut sich die Verbindung ohne erkennbare Fehlordnung aus isolierten Kalium‐Kationen und pyramidalen Silanid‐Anionen auf. Zur Koordinationssphäre beider Teilchen gehören sieben Gegenionen (K ⃛Si 356 bis 386 pm); beim Anion kommen zwei zusätzliche Kontakte zu gleichnamigen Nachbarn (Si ⃛Si 355 pm) hinzu. Die Kristallstruktur stellt eine Defektvariante des Baryt‐Typs dar, Verwandtschaft besteht aber auch zur Hochtemperatur‐Modifikation (α‐Form, Steinsalz‐Typ) und zum Caesium‐trihydrogengermanid (Thalliumiodid‐Typ).

Vibrational properties of β-KSiH3and β-RbSiH3: a combined Raman and inelastic neutron scattering study

“…At temperatures below 200 K, A SiH 3 adopts an ordered low‐temperature (β) modification. β‐KSiH 3 crystallizes with the orthorhombic space group Pnma . Silyl groups possess a local C s symmetry, which implies two different Si–H distances and H–Si–H bond angles (Fig.…”

Silylanions: Inversion Barriers and NMR Chemical Shifts

“…In the sodium alcoholate H 3 Si complex, however, the inverted form is more stable, as was proven by X‐ray structure analysis and ab initio calculations 40. In the case of H 3 SiK, the tetrahedral conformer has been found to be more stable 41, 42…”

“…Not only the silicon substituents, but also the choice of the counterion influence the stability of the silyl anion complexes 40–42. Calculations on H 3 SiNa show a preference for the tetrahedral minimum over the inverted structure (1.55 kcal mol −1 at the MP 4/6‐31G* level40).…”

Graft copolymerization of acrylic acid onto xanthum gum using a potassium monopersulfate/Fe2+ redox pair

“…In the 1960s, potassium silanide (KSiH 3 ) was synthesized by reacting silane (SiH 4 ) and potassium in 1,2‐dimethoxyethane at 195 K;14 an incomplete α‐cubic structure was reported,15 in which the hydrogen atomic positions remain unsolved. Almost three decades later, a low‐temperature orthorhombic β‐form of KSiH 3 was reported,16 in which hydrogen atoms were localized by using a difference Fourier map (mean d SiH =1.42 Å), but not refined. These structural data reveal that solid‐state metal silanides with short SiH bonds (as in silanes) do exist.…”

“…Although the KSiH 3 stoichiometry exhibits an appealing hydrogen content of 4.3 wt %, the potential applications for hydrogen storage remain unknown due to the lack of accurate crystallographic and thermodynamic data. By first using the β‐KSiH 3 structure,16 preliminary DFT calculations of the KSi/KSiH 3 thermodynamic equilibrium gave promising results, that is, a hydrogenation energy value of −35 kJ mol −1 H 2 17. However, the lack of precise structural data for the α‐KSiH 3 polymorph hinders the desired accurate prediction at temperatures for practical hydrogen storage.…”