NaRb 7 (Si 4– x Ge x ) 2 – Soluble Zintl Phases Containing Heteroatomic Tetrahedral ­[Si 4– x Ge x ] 4– Clusters

The quaternary phases NaRb 7 (Si 4– x Ge x ) 2 ( x  = 1–3) crystallize with an NaRb 7 Ge 8 ‐type structure and contain tetrahedral four‐atom clusters that consist of Si and Ge atoms. The quaternary phases possess larger cell volumes with increasing Ge amount. The formation of heteroatomic [Si 4– x Ge x ] 4– clusters is indicated by chemically different Si environments, which were analyzed by means of solid‐state 29 Si MAS (magic‐angle spinning) NMR spectroscopy of a 29 Si‐enriched NaRb 7 (Si 4– x Ge x ) 2 sample with x  = 0.5 as well as quantum chemical calculations of the NMR coupling parameters. NaRb 7 (Si 4– x Ge x ) 2 represents another rare example of a 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. In the presence of MesCu (Mes = mesityl) and 18‐crown‐6 as a sequestering agent, crystals with the composition [Rb(18‐crown‐6)] 2 Rb 2 [(MesCu) 2 (Si 4– x Ge x )](NH 3 ) 11 were isolated with x  = 2.2(1). [(MesCu) 2 (Si 4– x Ge x )] 4– represents another isomer of a MesCu‐stabilized tetrahedral anion and supports the observation that Zintl phases, which contain solely tetrahedranide subunits, represent a new class of soluble Zintl phases.