Helix-based supramolecular isomerism of metal–organic framework†
Rui-Li Sang,Li Xu
CrystEngComm Pub Date : 07/06/2010 00:00:00 , DOI:10.1039/C002677H
Abstract

Reactions of Na2Pra2biim [Na2Pra2biim = 1, 1′-di(propionic acid)-2, 2′-biimidazole disodium salt] and Cd(NO3)2·4H2O under different reaction conditions produce four helix-based (pseudo)supramolecular isomers of distinct structural topology: [Cd(Pra2biim)(H2O)]n·2H2O (1) with (42·62·122) topology, [Cd(Pra2biim)]n·nH2O (2) with (41·65) topology of CrB4, [Cd(Pra2biim)]n·2nH2O (3) with (43·123) topology and [Cd(H0.5Pra2biim)(H2O)2]2n·(ClO4)n (4) with (65·8) topology. Three kinds of helical chains built of N,N′-biim–Cd, η2-Pra2–Cd and η1-Pra2–Cd have been observed in 1–4, respectively. Compound 2 is the thermodynamically stable and compounds 1, 3, 4 are thermodynamically metastable. Conformation analysis of the ligand is presented to understand the flexibility of the Pra2biim2− that influences the assembly topological architectures. Chiral recognition between helical chains has been found in compound 3.

Graphical abstract: Helix-based supramolecular isomerism of metal–organic framework