Si94– Anions in Solution – Structures of the Solvates Rb4Si9·4.75NH3 and [Rb(18‐crown‐6)]Rb3Si9·4NH3, and Chemical Bonding in Si94–

Abstract

AbstractDissolving the ternary material K6Rb6Si17 together with chelating ligands such as 18‐crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane), dibenzo‐18‐crown‐6 (2,3,11,12‐dibenzo‐1,4,7,10,13,16‐hexaoxacyclooctadecane) and [2.2.2]cryptand(4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane)in liquid ammonia yields the solvates Rb4Si9·4.75NH3 and [Rb(18‐crown‐6)]Rb3Si9·4NH3. Single‐crystal X‐ray diffraction analysis reveals the presence of Si94– anions, the existence of which in solution has been a matter of discussion until now. In both compounds, the Si94– cages display slightly distorted monocapped square‐antiprismatic shapes. Additionally, quantum chemical calculations, NBO analysis and ELF (electron localisation function) considerations have been made to gain a deeper insight into the chemical bonding of this Zintl anion. The ELF analysis shows that, whereas the Wade–Mingos–Williams rules obviously apply for the prediction of the molecular shape of the anions, no evidence for three‐centre two‐electron bonding can be found. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)