Synergistic Ligand-Guest Engineering for Topological and Functional Control in Cobalt(II)-Based Metal-Organic Frameworks

Abstract

This study demonstrates synergistic ligand-guest engineering for precise topological and functional control in cobalt(II)-based metal-organic frameworks (MOFs). Two topology-tunable MOFs, T-MOF-1 and T-MOF-2, were synthesized using tailored ligands (L1 with flexible chains; L2 with π-conjugated moieties) and 4,4′-biphenyldicarboxylic acid. Encapsulation of aromatic guests (pyrene or coronene) dynamically modulated framework architectures: single-crystal X-ray diffraction revealed that pyrene induced lattice expansion in T-MOF-1 (unit cell volume: 5237 ų → 10,478 ų), while coronene triggered a topological transition from trigonal to monoclinic symmetry in T-MOF-2. These structural changes stemmed from guest-induced steric/electronic effects (π-π stacking, C-H···π interactions), enhancing thermal stability by 40–60 °C. Guest encapsulation also tailored optoelectronic properties—pyrene enhanced fluorescence intensity, whereas coronene caused quenching and redshifted emission. Nitrogen physisorption confirmed pore expansion, increasing specific surface areas (e.g., T-MOF-1: 72 → 243 m²·g⁻¹). This ligand-guest synergy establishes a paradigm for designing MOFs with adaptive topologies and functionalities for sensing, catalysis, and optoelectronics.