A 1D coordination network built from trimeric Co(II) units: synthesis, characterisation and gas sorption properties

Ligands based on bicyclo[2.2.2]oct-7-ene units have been used previously to obtain porous metal–organic materials, including 3D frameworks, 2D sheets, and discrete porous cages. The steric bulk of this unit helps to generate porosity in these materials, and so it has also been incorporated into porous organic cages for this purpose. In this contribution, we describe a new, nitro-functionalised ligand, LH₂, containing this unit, which yields a 1D coordination network, 1, upon reaction with cobalt(II) acetate. The ligand itself is found to crystallise readily, and we describe its crystal structure and gas sorption measurements for uptake of N₂. The coordination network 1 consists of linear, trinuclear Co(II) metal nodes that are bridged by pairs of ligands to create an intrinsic pore that is occupied by coordinated dimethylacetamide molecules (DMA). Solvent exchange and activation experiments were unsuccessful in removing DMA, but the orientation of the nitro-groups of the polymer into the space between the chains motivated CO₂ sorption studies at room temperature, reaching nearly 0.5 mmol/g at 20 bar of absolute pressure.