Dimers of Heptapnictide Anions: As₁₄^4- and P₁₄^4- in the Crystal Structures of [Rb(18-crown-6)]₄As₁₄·6NH₃ and [Li(NH₃)₄]₄P₁₄·NH₃

Compounds [Rb(18-crown-6)]4As14·6NH3 (1) and [Li(NH3)4]4P14·NH3 (2) were prepared by the reaction of Rb4As6 with SbPh3 and 18-crown-6 and by the reduction of white phosphorus with elemental lithium in liquid ammonia, respectively. Both were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the Ci symmetrical Pn144- anion (Pn = P, As), which consists of two nortricyclane-like Pn7-cages connected by a single bond. Molecular complexes of [Rb(18-crown-6)(NH3)]2[Rb(18-crown-6)]2As14 are formed in 1, which are connected to fanfold sheets via N−H···O bonds. The anion is isolated in 2, and N−H···N bonds result in the formation of {[Li(NH3)4](μ-NH3)2[Li(NH3)4]}2+ cationic complexes.