Detection of the Elusive Highly Charged Zintl Ions Si₄⁴⁻ and Sn₄⁴⁻ in Liquid Ammonia by NMR Spectroscopy

Abstract

It's detected! The existence of the prototypical Zintl ions Tt44− (Tt=Group 14 element), which are isoelectronic to the P4 molecule, used to be confined to the solid state. Recently, circumstantial evidence for a solution chemistry in liquid ammonia emerged. Direct spectroscopic observation of the dissolved anions has now been achieved. In the case of Si44−, this is the first solution detection of any homoatomic silicide.

NaRb7(Si4–xGex)2 – Soluble Zintl Phases Containing Heteroatomic Tetrahedral ­[Si4–xGex]4– Clusters

“…The compositions result from a full occupancy of Wyckoff position 8c (Si1) with Ge in the first case, while Wyckoff position 24d (Si2) was substituted by Ge atoms in the second case. For x = 1, corresponding to Ge on Si1, an isotropic 29 Si shift of δ = -294.9 ppm was calculated and is in good agreement with the experimental shift value of the Si2Ј environment (Table 1). On the other hand, a prominently downfield-shifted isotropic 29 Si shift of δ = -244.1 ppm was calculated for x = 3 (Ge on Si2) but was experimentally not detected.…”

“…This influence is known for atomic disorder in intermetallic phases [28] and indicates the presence of mixed tetrahedral Si/Ge clusters in the investigated compound. 29 Si MAS NMR spectroscopic measurements underline these observations (Figure 2b). Two signals at δ = -344.9 and -325.7 ppm are comparable with those in Rb 7 NaSi 8 [26] and can be attributed to the Si1 and Si2 environments of 2 .…”

“…This value is in good agreement with the quantum mechanical calculated isotropic shift of δ = -294.9 ppm for the Si2 atoms in NaRb 7 (Si 4-x Ge x ) 2 with x = 1 ( Table 1). Thus, it is reasonable that the experimentally determined downfield shifted 29 Si NMR signal of NaRb 7 (Si 4-x Ge x ) 2 with x = 0.5 can be attributed to the chemically different environment of Si2Ј, which consists of mixed Si/Ge clusters. Furthermore, a preferred partial occupancy of the Si1 atoms by Ge in the…”

“…4-clusters that still seem to be present in NaRb 7 (Si 4-x Ge x ) 2 with x = 0.5 (Table 1). A third 29 Si NMR signal at a more positive frequency of δ = -305.6 ppm results from an Si environment being influenced by the Ge atoms due to partial substitution in the [Si 4 ] 4-clusters. This value is in good agreement with the quantum mechanical calculated isotropic shift of δ = -294.9 ppm for the Si2 atoms in NaRb 7 (Si 4-x Ge x ) 2 with x = 1 ( Table 1).…”

Isolierung und vielseitige Derivatisierung eines ungesättigten anionischen Siliciumclusters (Silicoid)

“…[13,14] Angestoßen durch neuartige Verfahren zur Extraktion aus Festphasen in polare Lçsungsmittel wie flüs-sigen Ammoniak, [15] Ethylendiamin [16] oder Dimethylformamid [17] wurde in den letzten Jahren das Potential der ZintlAnionen als Bausteine für erweiterte Systeme erkannt. Dementsprechend sind für Gruppe-14-Elemente,d ie schwerer als Silicium sind, stäbchenartige Polyanionen, [18] Nanopartikel [19] oder mesostrukturierte Allotrope der Elemente [20] zugänglich.…”