4-Carb­oxy­pyridinium perchlorate 18-crown-6 dihydrate clathrate and 4-carb­oxy­pyridinium tetra­fluoro­borate 18-crown-6 dihydrate clathrate

Mixtures of 4-carb­oxy­pyridinium perchlorate or 4-carb­oxy­pyridinium tetra­fluoro­borate and 18-crown-6 (1,4,7,10,13,16-hexa­oxacyclo­octa­decane) in ethanol and water solution yielded the title supra­molecular salts, C₆H₆NO₂⁺·ClO₄⁻·C₁₂H₂₄O₆·2H₂O and C₆H₆NO₂⁺·BF₄⁻·C₁₂H₂₄O₆·2H₂O. Based on their similar crystal symmetries, unit cells and supra­molecular assemblies, the salts are essentially isostructural. The asymmetric unit in each structure includes one protonated isonicotinic acid cation and one crown ether mol­ecule, which together give a [(C₆H₆NO₂)(18-crown-6)]⁺ supra­molecular cation. N—H...O hydrogen bonds between the protonated N atoms and a single O atom of each crown ether result in the 4-carb­oxy­pyridinium cations `perching' on the 18-crown-6 mol­ecules. Further hydrogen-bonding inter­actions involving the supra­molecular cation and both water mol­ecules form a one-dimensional zigzag chain that propagates along the crystallographic c direction. O—H...O or O—H...F hydrogen bonds between one of the water mol­ecules and the anions fix the anion positions as pendant upon this chain, without further increasing the dimensionality of the supra­molecular network.