Syntheses and structures of piperazin-1-ium ABr2 (A = Cs or Rb): hybrid solids containing 'curtain wall' layers of face- and edge-sharing ABr6 trigonal prisms.

The isostructural title compounds, poly[piperazin-1-ium [di-μ-bromido-caesium]], {(C4H11N2)[CsBr2]} n , and poly[piperazin-1-ium [di-μ-bromido-rubidium]], {(C4H11N2)[RbBr2]} n , contain singly-protonated piperazin-1-ium cations and unusual ABr6 (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.