Monodisperse metal-organic cages for gas chromatographic separation

Establishing the definitive structure–performance relationship in metal-organic cage (MOC) stationary phases requires isolating intrinsic cavity contributions from dispersion-induced artifacts. However, solvent-dependent dispersion behavior of MOCs often obscures the direct role of molecular cage architecture in chromatographic separation. Here, we constructed a structurally homologous series of Zr-based MOCs with identical V₄F₄ topology but systematically enlarged cavity and window sizes through ligand elongation, including two newly constructed cages. Systematic investigation of solvent-dependent behavior revealed distinct states ranging from crystalline assemblies to oligomeric aggregates and ultimately to monodisperse cages. When utilized as gas chromatographic (GC) stationary phases, only monodisperse Zr-MOCs translated their discrete cage architectures into efficient separations, establishing dispersion control as a prerequisite for accessing intrinsic structure–property relationships. Under monodisperse conditions, Zr-MOC-BBC (BBC = 1,3,5-tris(4'-carboxy[1,1'-biphenyl]-4-yl)benzene) with the largest cavity exhibited the highest separation resolution compared to Zr-MOC-BTB (BTB = 1,3,5-tris(4-carboxyphenyl)-benzene) and Zr-MOC-BTE (BTE = 4,4',4''-(benzene-1,3,5-triyltris(ethyne-2,1-diyl))tribenzoic acid). Mechanistic analysis demonstrated that the dispersion state primarily governed diffusion-controlled mass transfer, whereas intrinsic cavity size influenced both mass transfer resistance and thermodynamic host–guest interactions. This work demonstrates that controlling dispersion state is essential for accessing the intrinsic cavity and provides insights into the design of MOC-based separation materials.