Metallo‐Käfige für Metall‐Anionen: Hochgeladene [Co@Ge₉]⁵⁻‐ und [Ru@Sn₉]⁶⁻‐Cluster mit sphärisch eingelagerten Co⁻‐ und Ru²⁻‐ Anionen

Abstract

Endohedrale Cluster gelten als molekulare Modelle für intermetallische Verbindungen – eine Verbindungsklasse mit kaum verstandenen Bindungsprinzipien. Wir berichten hier über lösliche Clusteranionen mit den bisher höchsten Ladungen pro Clustereinheit. Die Cluster zeigen die große Ähnlichkeit zwischen intermetalloiden Clustern und den entsprechenden Koordinationspolyedern in intermetallischen Verbindungen auf. Während bereits viele endohedrale Zintl‐Ionen über Reaktionen in Lösung erhalten wurden, haben wir nun die Raman‐Spektroskopie als eine zuverlässige Sonde für den erstmaligen Nachweis von diskreten endohedral gefüllten Clustern in intermetallischen Phasen etabliert. Die ternären Vorläuferlegierungen der nominellen Zusammensetzungen “K5Co1.2Ge9” und “K4Ru3Sn7” zeigen charakteristische Bindungsmoden, die von Metallatomen im Zentrum polyedrischer Cluster herrühren, was zeigt, dass in diesen Legierungen gefüllte Cluster vorliegen. Außerdem berichten wir über die strukturelle Charakterisierung von [Co@Ge9]5− (1a) und [Ru@Sn9]6− (2a), die aus Lösungen der entsprechenden Legierungen erhalten wurden.

Investigations on the Solubility of Sn4‐Cluster Compounds in Liquid Ammonia

“…The two independent OHions are closely surrounded by quite regular square pyramids of five K cations each (Figure 5b), and such [OK 5 ] groups with a varying number of coordinating NH 3 molecules have been found as a common feature of all known related compounds. [18,[25][26][27] While this building group with short intra-"molecular" bonds usually shows significantly longer KÀ O/KÀ N distances between different units and can be considered as an almost isolated entity, in the present structure two of these distorted pyramids are fused into K 7 (OH) 2 pairs by sharing one common triangular face, and are further connected via opposite vertices to form strands parallel to the b axis, as shown in Figure 6.…”

“…[31] In the current experiments the origin of the hydroxide impurity, beside that it is very probably resulting from a contamination with water which was deprotonated latest by ammonia, could not have been detected so far. It might be introduced accidentally by the use of incompletely dried ammonia, which was the only common ingredient in related experiments including Si, Ge or Sn clusters, [18,[25][26][27] however, also a contamination of the alkali metal which was dragged along through the precursor synthesis, cannot be excluded. Obviously not reactive with tetrel Zintl anions at temperatures of liquid ammonia, it may act as an additive to support crystallisation.…”

“…4À besides Si 4 4À clusters, in both cases again in presence of ingredients of uncertain function, [(C 6 H 5 ) 3 P] 2 Ni(CO) 2 [13] or dibenzo- [18]crown-6 and AuPPh 3 Cl, [14] which were not found in the crystallized product. Related experiments including Ge, namely of Rb 6 K 6 Ge 17 with diphenyl zinc and [18]crown-6, resulted in an edge-on protonated Ge 4 cluster with a two-electron-threecenter GeÀ HÀ Ge bond, [15] and very recently, a Si 4 cluster even in a sixfold η 2 coordination by Au complexes has been found after reaction of Cs 6 Rb 6 Si 17 and NHC tBu AuCl. [16] The role of organo-metallic reagents towards the solubility of A 4 Sn 4 phases was lately pointed out for Rb 4 Sn 4 .…”

“…[8] Special reaction conditions had been applied, often simply due to the fact that originally other products or reactions were intended which also lead to transition metal complexes of tetrahedral cluster anions like Rb 6 [(η 2 -Sn 4 )Zn(η 3 -Sn 4 )] • 5 NH 3 [11] and K 7 [(η 2 -Sn 4 )Au(η 2 -Sn 4 )] • 16 NH 3 . [12] A simple dissolution of Na 4 Sn 4 was successfully carried out in presence of [18]crown-6 and mesityl copper, which were not found in the solid product, [9] and the Cs compound was synthesized form tetraphenyl tin and an excess of elemental Cs. [10] [Li(NH 3 ) 4 ] 4 Sn 4 • 4 NH 3 , Na 4 Sn 4 • 11.5 NH 3 , [8] and Rb 4 Sn 4 • 2 NH 3 [10] were prepared from solutions of elemental alkali metal and Sn, in cases of Li and Na, also t BuOH was added.…”

“…[16] The role of organo-metallic reagents towards the solubility of A 4 Sn 4 phases was lately pointed out for Rb 4 Sn 4 . [17] Recently, we have investigated the appearance of intermetalloid clusters in solution, [18][19] and for the syntheses several intermetallic precursors have been studied. To open the synthetic potential of such intermetalloid clusters also experiments in solution are highly desired, and liquid ammonia is the first choice for such attempts.…”