Synthesis, characterization, and magnetic studies of a series of metal–mellitate coordination polymers

Abstract

Benzenehexacarboxylic acid, also known as mellitic acid, reacts readily with cobalt and manganese chlorides to afford a new series of coordination polymers. Three of them are cobalt mellitates (1–3) synthesized at different conditions, i.e. either at room temperature (1) or hydrothermally at 140 (2) and 180 °C (3), the last two in the presence of organic bases. While compound 1 exhibits chains held together by inter-chain hydrogen bonds, compounds 2 and 3 are three-dimensional as could be expected from the synthetic conditions. The latter two structures display complicated connectivity and unusual multi-nodal topologies that have not been observed before. The two manganese compounds contain the nitrogen-based chelating co-ligands 2,2′-bpy or 1,10-phen for 4 and 5, respectively. Due to the pairs of blocked sites by the terminal co-ligands, both structures are low dimensional exhibiting chains in 4 and layers in 5. At the same time, π–π interactions between the co-ligands and multiple inter-chain/layer hydrogen bonds stitch the chains/layers into overall 3D supramolecular frameworks. Magnetic measurements on compounds 2–5 showed that they all exhibit dominant antiferromagnetic coupling. However, the details of the antiferromagnetic behavior are different, and this is consistent with the different structural characteristics.