Si 4 4– in Solution – First Solvate Crystal Structure of the Ligand‐free Tetrasilicide Tetraanion in Rb 1.2 K 2.8 Si 4 ·7NH 3

We report the first solvate structure of the silicide anion Si 4 4– , which provides circumstantial evidence of the stability of the highly charged anion in liquid ammonia solutions. The solvate Rb 1.2 K 2.8 Si 4 · 7NH 3 crystallized from a mixture of the ternary compound K 6 Rb 6 Si 17 with the transition metal complex [(C 6 H 5 ) 3 P] 2 Ni(CO) 2 [bis(triphenylphosphine)dicarbonylnickel] in the presence of the chelating agents 18‐crown‐6 (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. Single X‐ray diffraction analysis confirms the presence of the Si 4 4– anion in the crystal structure of Rb 1.2 K 2.8 Si 4 · 7NH 3 , which represents the first solvate compound of the naked tetrasilicide tetraanion. All five crystallographically independent cation positions show mixed occupancy by Rb + and K + .