Metamagnetic behavior and moisture-absorption induced reversible network assembly of a cobalt-1,2,4-benzenetricarboxylate supramolecular network

A Co(II) 1,2,4-benzenetricarboxylate supramolecular network, {Co[C₆H₃(CO₂)₂(CO₂H)](H₂O)₂·H₂O}_n (FJU-4) was synthesized from an unsymmetrical ligand, namely 1,2,4-benzenetricarboxylic acid (H₃btc), under pH-controlled hydrothermal conditions. FJU-4 has a 2D layered structure with an interdigitated pendent-arm, composed of a carboxylate- and a water-bridged cobalt chain, which are united to generate a 3D supramolecular structure through interlayer hydrogen bonding and π–π interactions between the phenyl rings, carboxyl groups, and guest water molecules. The assembly of the FJU-4 network is a reversible process, as the result of changes in noncovalent interactions triggered by dehydration and the absorption of moisture. A magnetic analysis showed that FJU-4 exhibits metamagnetic behavior resulting from spin-canting magnetization while heat capacity measurements indicated that FJU-4 undergoes long range magnetic ordering at 2.6 K.