Dimers of heptapnictide anions:: As144- and P144- in the crystal structures of [Rb(18-crown-6)]4As14•6NH3 and [Li(NH3)4]4P14•NH3

Compounds [Rb(18-crown-6)](4)As(14)(.)6NH(3) (1) and [Li(NH3)(4)](4)(P14NH3)-N-. (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 C-i symmetrical Pn(14)(4-) anion (Pn = P, As), which consists of two nortricyclane-like Pn(7)-cages connected by a single bond. Molecular complexes of [Rb(18-crown-6)(NH3)](2)[Rb(18-crown-6)](2)As-14 are formed in 1, which are connected to fanfold sheets via N-H center dot center dot center dot O bonds. The anion is isolated in 2, and N-H center dot center dot center dot N bonds result in the formation of {[Li(NH3)(4)](mu-NH3)(2)[Li(NH3)(4)]}(2+) cationic complexes.