A Planar Bibridged Cu₁₀Br₂₂^2- Oligomer: Dimensional Reduction and Recombination of the CuBr₂ Lattice via the N−H···Br^- and the C−Br···Br^- Synthons

Abstract

A retro-crystal engineering analysis is given of the microporous stepped layer structure observed in the compound (35DBP)2Cu10Br22 (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-)n ribbons occurs via the action of the 35DBP+ “molecular scissors”. These ribbons have the Geiser notation of n(t∥, t⊥) = 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.