Hydrogen-bond-directing effect in the ionothermal synthesis of metal coordination polymers

Abstract

Four new cobalt coordination polymers, (EMIm)[Co₂(TMA–H)₂(44bpy)₃]Br 1, (EMIm)[Co(TMA–H)(44bpy)₂](44bpy)Br 2, (EMIm)[Co(TMA)(Im–H)] 3 and (EMIm)₂[Co(TMA)₂(TED–H₂)] 4, were prepared from 1-ethyl-3-methyl imidazolium bromide (EMIm–Br). All the compounds have similar two-dimensional cobalt trimesate (TMA) coordination layers but different three-dimensional supramolecular architectures that contain one of three potentially ditopic amines, 4,4′-bipyridine (44bpy), imidazole (Im–H) and triethylenediamine (TED). Two-fold interpenetration of hydrogen-bonding networks was found for 1, 2 and 4. The coordination layers of 1 and 2 are neutral while 3 and 4 have anionic molecular assemblies. The use of organic amines, that act as supramolecular bridging ligands, introduces hydrogen-bond-directing effects in the ionothermal synthesis of metal coordination polymers. Hydrogen bonding helps to align the packing between the coordination layers and control the formation of 3D supramolecular networks. In 1, hydrogen bonds between the ionic species within the channels direct the alignment of non-directional electrostatic interactions between EMIm⁺ and Br⁻ ions, which is a rare case of a hydrogen-bond-templating effect of ionic liquids in ionothermal synthesis.