Figure 1. Compounds used in this study and the X-ray structure^4b of 1a₂·4 with PF₆ counterions removed.

Figure 2. Partial proton NMR spectra (400 MHz, acetone-d₆, 22 °C) of bispyridinium salt 2a (a, bottom), cryptand 1a (b, middle), and 6.00 mM 1a and 3.00 mM 2a (c, top).

Figure 3. Mole ratio plot for 1a and 2a, indicating 2:1 stoichiometry. The solvent is acetone-d₆. [2a]₀=0.250 mM.

Figure 4. Scatchard plot for the complexation of cryptand host 1a with bispyridinium guest 2a in acetone-d₆ at 22 °C. p=fraction of monopyridinium units bound. Error bars in p: ±0.03 absolute; error bars in p/[1a]: ±0.06 relative.

Figure 5. Ball-stick (a, top) and space-filling (b, bottom) views of the X-ray structure of 1a₂·2a. (a) Molecules 1a are red, 2a is blue, water molecules are magenta, oxygens are green, and nitrogens are yellow. Two PF₆ counterions, other solvent molecules, and the hydrogens except the ones involved in hydrogen bonding were omitted for clarity. Hydrogen-bond parameters: C(O)O distances (Å), HO distances (Å), C(O)–HO angles (°) at A, 3.42, 2.53, 150; B, 3.21, 2.26, 161; C, 2.99, 2.15, 171; D, 2.92, 2.08, 173; E, 3.06, 2.28, 140; F, 3.41, 2.47, 170. Face-to-face π-stacking parameters: centroid–centroid distances (Å) 3.74, 3.66; ring plane/ring plane inclinations (°) 9.1, 4.8. (b) All protons, two PF₆ counterions, and other solvent molecules were omitted. Molecules 1a are red, 2a is blue, and the water molecules are green.

Figure 6. Ball-stick (a, top) and space-filling (b, bottom) views of the X-ray structure of 1a₂·2b. (a) Molecules 1a are red, 2b is blue, water molecules are magenta, oxygens are green, and nitrogens are yellow. Two PF₆ counterions, other solvent molecules, and the hydrogens except the ones involved in hydrogen bonding were omitted for clarity. Hydrogen-bond parameters: C(O)O distances (Å), HO distances (Å), C(O)–HO angles (°) at G, 3.31, 2.45, 144; H, 3.34, 2.35, 171; I, 2.93, 1.97, 168; J, 2.85, 1.92, 167; K, 3.04, 2.32, 129; L, 3.25, 2.26, 173. Face-to-face π-stacking parameters: centroid–centroid distances (Å) 3.80, 3.74; ring plane/ring plane inclinations (°) 6.4, 5.4. (b) All protons, the PF₆ counterions, and other solvent molecules were omitted. Molecules 1a are red, 2b is blue, and the water molecules are green.

Figure 7. Ball-stick (a, top) and space-filling (b, bottom) views of the X-ray structure of 1b₂·2b. (a) Molecules 1b are red, 2b is blue, oxygens are green, and nitrogens are yellow. Two PF₆ counterions, solvent molecules, and the hydrogens except the ones involved in hydrogen bonding were omitted for clarity. Hydrogen-bond parameters: CO distances (Å), HO distances (Å), C–HO angles (°) at M, 3.40, 2.52, 148; N, 3.37, 2.57, 138; O, 3.48, 2.56, 165. Face-to-face π-stacking parameters: centroid–centroid distances (Å) 4.03, 3.87; ring plane/ring plane inclinations (°) 7.5, 5.3. (b) All protons, the PF₆ counterions and solvent molecules were omitted. Molecules 1b are red and 2b is blue.