A planar bibridged Cu10Br222- oligomer:: Dimensional reduction and recombination of the CuBr2 lattice via the N-H•••Br- and the C-Br•••Br- synthons

A retro-crystal engineering analysis is given of the microporous stepped layer structure observed in the compound (35DBP)(2)Cu10Br22 (where 35DBP(+) is the 3,5-dibromopyridinium cation). The assembly of the anionic layer structure can be envisioned as occurring in two steps. First, dimensional reduction of the parent CuBr2 structure into (Cu10Br222-), ribbons occurs via the action of the 35DBP(+) "molecular scissors". These ribbons have the Geiser notation of n(t(parallel to), t(perpendicular to)) = 10(7/2, 1/2). Next, the ribbons are recombined into stepped layers with the concomitant reconstruction of the semi-coordinate Cu...Br bonds. These layers aggregate through synthonic interactions between the 35DBP(+) cations and the bromide ions in the layers. The combination of N-H...Br- and the C-Br...Br- synthons define bibridged [Br- - (35DBP(+))(2) - Br-] units that tie the layers together. These bibridged units are linked into cationic chains via C-H... Br- interactions. It is observed that the nesting of these chains produces a cationic layer that is commensurate with the stepped anionic layer. This mutual commensuration gives rationale for the length of the Cu10Br222- oligomers.