Second Auxiliary Ligand Effects on Coordination Polymer Structure: Regulating Metal-Organic Framework Properties

Metal-organic frameworks (MOFs) represent a revolutionary class of porous materials with exceptional tunability in their structural and functional properties. The incorporation of second auxiliary ligands into coordination polymer systems has emerged as a powerful strategy for controlling framework architecture, porosity, and functionality. This review examines the fundamental principles governing how auxiliary ligands influence MOF formation, structural polymorphism, and resultant properties. The modulator-driven approach enables precise control over crystal growth kinetics, defect formation, and framework topology. Second auxiliary ligands demonstrate remarkable capability in directing interpenetration patterns, controlling pore dimensions, and enhancing chemical stability. Furthermore, these ligands significantly impact functional properties including gas adsorption capacity, catalytic activity, and biological inhibition mechanisms. The strategic selection of auxiliary ligands with varying geometries, electronic properties, and coordination preferences allows for systematic property optimization. Recent advances in reticular chemistry have revealed that auxiliary ligand effects extend beyond simple structure direction to encompass sophisticated control over framework flexibility, guest accommodation, and responsive behavior. This comprehensive analysis highlights the critical role of auxiliary ligands in advancing MOF design principles and expanding their applications across diverse technological domains.