[(MesCu)₂(η³‐Si₄)]⁴⁻: A Mesitylcopper‐Stabilized Tetrasilicide Tetraanion

Abstract

Between Zintl and Wiberg: The tetrahedral silicon cluster [(MesCu)2Si4]4− was obtained from the reaction of K6Rb6Si17 and MesCu (Mes=2,4,6‐Me3C6H2) in liquid ammonia. Through stabilization with transition metal fragments, highly charged silicon clusters can thus be transferred and handled in solution.

First Incorporation of the Tetrahedral [Sn4]4- Cluster into a Discrete Solvate Na4[Sn4] (NH3)13 from Solutions of Na4Sn4 in Liquid Ammonia

“…From a mixture of Na 4 Sn 4 , 18-crown-6 and CuMes, black block-shaped crystals could be isolated after several weeks of storage. A structure determination led to the composition Na 4 Sn 4 (NH 3 ) 13 (1, Fig. 1 and Table 1).…”

“…In the presence of CuMes and 18-crown-6, Na 4 Sn 4 was found to be soluble with formation of deep-red suspensions, from which crystals of the composition Na 4 Sn 4 (NH 3 ) 13 can be grown. The role of CuMes and the sequestering …”

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Treatment of solutions of Na 4 Sn 4 in liquid ammonia with CuMes (Mes = mesityl) and 18-crown-6 afforded crystals of the composition Na 4 [Sn 4 ]·(NH 3 ) 13 . The structure features anionic units {Na 7 [Sn 4 ] 2 } and separate Na cations, both fully solvated by ammonia molecules.

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Mixed Tetrahedral Zintl Clusters: Single Crystal Structure Determination of [Si4‐xGex]4−, [(MesCu)2(Si4‐xGex)]4−, and the 29Si MAS NMR Spectra of A4Si2Ge2 (A=K, Rb)

“…Powdered samples of K 4 Si 2 Ge 2 and Rb 4 Si 2 Ge 2 both exhibit one broad peak at À39 ppm and À44 ppm, respectively (see Figure 3 a and b, respectively). Corresponding signals for A 4 Si 4 phases appear with a strong upfield shift at around À300 ppm and show a slight shift depending on the nature of the metal A: À363 ppm for A = Na, [21] À330 ppm for A = K , [16,22] À310 ppm for A = K/Rb, [16,22] and À290 ppm for A = Rb. [16,22] In the solid solution Mg 2 Si 1Àx Ge x (x 0.9), in which the atoms E do not form E À E bonds a downfield shift of approximately 10 ppm of the 29 Si MAS NMR signal is observed with increasing amounts of Ge.…”

“…[22] The asymmetric unit of crystals of 2 contains the fourfold negatively charged heteroatomic polyanion [(MesCu) 2 4À clusters in crystals of 2 leading to an equal occupation ratio can be excluded. As observed in [(MesCu) 2 Si 4 ] 4À , [22] the central structural motif in 2 a consists of a slightly distorted tetrahedron capped by two MesCu fragments (Figure 4). Except for dA C H T U N G T R E N N U N G (E1-E4) = 2.643(2) that is bridged by two MesCu fragments, all E-E bonds within the tetrahedral unit range from 2.453(2) to 2.490 (2) .…”