Magnetic and Porous Regulation in Cobalt(II) Hydrogen-Bonded Organic Framework via Supramolecular Isomerism

Supramolecular isomerism has been recognized as an effective strategy for manipulating structures and properties, particularly in metal-hydrogen-bonded organic frameworks (MHOFs). However, it has been less studied in the context of magnetic dynamics. In this study, we reinvestigated two previously reported cobalt(II) HOFs, {[(H2O)(2)Co(Hbic)(2)]sol}(n) (H(2)bic = 1H-benzimidazole-5-carboxylic acid; 1, Sol = 2DMF1.5H(2)O; 2, Sol = H2O), which exhibit unique supramolecular isomerism. In both complexes, octahedral Co(II) ions are connected by deprotonated Hbic-ligands to form one-dimensional chains, which are then sustained into three-dimensional frameworks by prominent N-HO hydrogen-bonding interactions. This results in significantly different porosities and N-2-adsorption abilities: a high solvent-accessible void of 46.2% for the desolvated phase of 1, compared to only 2.3% for that of 2, likely due to the additional pi-pi stacking interactions. Interestingly, our magnetic studies revealed that both 1 and 2 exhibit typical single ion magnet behaviors, with alternating relaxation dynamics (Raman, direct, and QTM for 1; Raman and direct for 2). These findings demonstrate that the structures, stability, porosities, and magnetic properties of MHOF materials can be effectively tuned through a supramolecular isomerization approach.