A 2-D coordination polymer incorporating cobalt(ii), 2-sulfoterephthalate and the flexible bridging ligand 1,3-di(4-pyridyl)propane

Abstract

The cobalt derivative {[Co₃(2-stp)₂(dpp)₄]·2H₂O}_n (1) has been hydro(solvo)thermally synthesised by combining sodium 2-sulfoterephthalic acid (2-stpH₂Na) and divalent cobalt nitrate in presence of the flexible N-donor co-ligand dpp (1,3-di(4-pyridyl)propane). Single-crystal X-ray diffraction shows that 1 is a two-dimensional coordination polymer with carboxylate and sulfonate oxygens and pyridyl nitrogens coordinated to the two symmetry independent octahedral cobalt(II) centres. UV-Vis, magnetic and EPR studies show that the cobalt(II) centres are high-spin. Compound 1 proved to be robust to the removal of the solvent water molecules, which was achieved by heating the sample to yield the desolvated complex {[Co₃(2-stp)₂(dpp)₄]}_n (2). 2 was also characterised by single-crystal X-ray diffraction at 331 K. Gas sorption studies on this material showed only surface binding of N₂ and modest uptake for CO₂. The crystallographic analysis also shows that upon desolvation, the flexible propyl groups of the dpp ligand adjust their positions, reducing the potentially accessible void volumes and accounting for the gas adsorption results.