Mixed Tetrahedral Zintl Clusters: Single Crystal Structure Determination of [Si_4‐xGe_x]⁴⁻, [(MesCu)₂(Si_4‐xGe_x)]⁴⁻, and the ²⁹Si MAS NMR Spectra of A₄Si₂Ge₂ (A=K, Rb)

Abstract

Mixing Si and Ge: An important step towards the formation of Si–Ge mixed semiconducting materials has been taken. The ternary Zintl phases A4Si2Ge2 and Rb12Si12Ge5 contain a heteroatomic [Si4−xGex]4− Zintl cluster. The mixed clusters have been isolated from solution in form of the salt [Rb([18]−crown–6)]2Rb2[(MesCu)2(Si3.3(1)Ge0.7(1))](NH3)12 (see figure).

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

“…[6][7][8] The E1-E4 bond [2.702(2) Å; highlighted in light grey in Figure 3] is 4-matches with x = 2.2(1) within standard deviations (3σ limit) the values of the precursor phase NaRb 7 (Si 2 Ge 2 ) 2 . A small change in the E-E bond length compared with homoatomic Si 4 or Ge 4 clusters is visible in 2a, while a change of positional or anisotropic displacement parameters is not noticeable from the comparative picture illustrated in Figure S5 in the Supporting Information.…”

“…Either a mixture of the elements Na, Rb, Si and Ge in the molar ratio 1:7:2:2, a mixture of the alkali metals and an Si/Ge alloy with equal amounts of Si and Ge, which had been ballmilled before use, or an appropriate mixture of the two ternary precursor phases Na 4 Si 2 Ge 2 /Rb 4 Si 2 Ge 2 = 1:7 was sealed in a tantalum container and heated to 600°C according to heating sequence 1 (see Experimental Section for details). [7,25] All reaction products were analyzed by powder X-ray diffraction methods. Indexing of the resultant X-ray powder diagrams indicates cubic cell parameters ranging between the values seen for the homoatomic analogues NaRb 7 Si 8 and NaRb 7 Ge 8 .…”

“…E-E bond lengths within the heteroatomic tetrahedra in 1a range from 2.469(2) to 2.584(2) Å [cf. 2.436(2)-2.548(2) Å in 1b and 2.39-2.47 Å in NaRb 7 Si 8 ].…”

“…Therefore, an ammonia solution of NaRb 7 (Si 2 Ge 2 ) 2 was treated with 18-crown-6 and MesCu. 4-(x = 0, 0.7, 4) [6][7][8] (2a, Figure 3 (3), [6] however with less NH 3 solvate molecules.…”

“…[6][7][8][9] 13 and Rb 4 Pb 4 (NH 3 ) 2 were isolated from the tetrahedral Zintl phases Na 4 Sn 4 and Rb 4 Pb 4 , respectively. [10] Residual experiments were carried out with A 12 E 17 phases (A = K-Cs, E = Si, Si/Ge) [7,[11][12][13] containing [E 9 ] 4-clusters next to phase with exclusively tetrahedral clusters that readily dissolves in liquid ammonia. The nature of the heteroatomic clusters was further investigated by dissolution of NaRb 7 -(Si 4-x Ge x ) 2 with x = 2 in liquid ammonia.…”