Triangulation of Guest Species in Porous Frameworks Using Solid-State NMR Spectroscopy and Quantum Chemical...

Porous functional materials, such as zeolites and metal-organic frameworks (MOFs), are invaluable to chemical industries due to their high surface areas and chemical versatility. Understanding how the active sites of these materials interact with adsorbates is crucial yet challenging. Solid-state (ss)NMR spectroscopy, while powerful, often requires complementary neutron or synchrotron-based diffraction techniques to precisely locate adsorbed species. Herein, 3-fluoropyridine serves as a probe molecule for ssNMR analysis to elucidate adsorption sites within UiO-66(Zr), a prototypical MOF. The high NMR receptivity of ¹⁹F and its sensitivity to its surrounding environment enable the site-specific characterization of host-guest interactions. When combined with density functional theory calculations and numerical simulations, structurally realistic adsorption models can be evaluated against experimentally derived spatial constraints. Results indicate specific binding of 3-fluoropyridine to bridging hydroxyl Bro̷nsted acid sites and Lewis acid sites at defects, with stabilizing orientations governed by hydrogen bonding and π···π interactions. This work establishes an experimental-computational approach applicable to porous frameworks, offering molecular-level insights into adsorption structures relevant to material design for enhanced and tailored functionality.