To further probe the nature of these guest binding interactions within MOC, single-crystal X-ray diffraction studies of MOC and its three host-guest complexes were performed (see Supporting Information section "Single-Crystal X-Ray Diffraction" for details on crystal growth and characterization). The crystal structures of MOC, HSO4⊂MOC, NO3⊂MOC, and DAQ⊂MOC are shown in Figure . In all cases, the added guest molecules reside within the cavity of the MOC. Consistent with 1 H NMR studies, hydrogen bonding interactions are observed between guest molecules and interior proton Ha, with bond distances ranging from 2.35 to 2.75 Å for all added guests. Interestingly, guest orientation was consistent with that of MOC packing for both OTf⊂MOC and DAQ⊂MOC (i.e., guest molecules were oriented in a consistent fashion throughout the crystal) perhaps due to their size relative to the MOC cavity; however, the position of NO3 and HSO4 within their respective hosts was observed to be split between 'top' and 'bottom' hydrogen bonding sites, as judged by equal electron density in both positions, but with relative intensity ~half that of the MOC structure, consistent with 1:1 binding as observed from titration experiments. Despite having the highest measured Ka, DAQ shows the longest hydrogen bonding distances; complementary ArH⋯ 𝜋 interactions are observed between He of the MOC and the flanking aryl rings of DAQ. This ArH⋯ 𝜋 interaction is hypothesized to drive the stronger binding and larger ligand distortion and desymmetrization of the cavity in DAQ⊂MOC, as compared to MOC, HSO4⊂MOC and NO3⊂MOC as judged by the angles between pyridine ligands (an average deviation from 90° of 1.86° as compared to 1.03°, 1.07°, and 0.36°, respectively. See