Syntheses and structures of piperazin-1-ium ABr(2) (A = Cs or Rb): hybrid solids containing 'curtain wall' layers of face- and edge-sharing ABr(6) trigonal prisms.

The isostructural title compounds, poly[piperazin-1-ium [di-μ-bromido-caesium]], {(C(4)H(11)N(2))[CsBr(2)]} (n) , and poly[piperazin-1-ium [di-μ-bromido-rubidium]], {(C(4)H(11)N(2))[RbBr(2)]} (n) , contain singly-protonated piperazin-1-ium cations and unusual ABr(6) (A = Cs or Rb) trigonal prisms. The prisms are linked into a distinctive 'curtain wall' arrangement propagating in the (010) plane by face and edge sharing. In each case, a network of N-H⋯N, N-H⋯Br and N-H⋯(Br,Br) hydrogen bonds consolidates the structure.