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, C(6)H(6)NO(2)(+)·ClO(4)(-)·C(12)H(24)O(6)·2H(2)O and C(6)H(6)NO(2)(+)·BF(4)(-)·C(12)H(24)O(6)·2H(2)O. 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 (C(6)H(6)NO(2))(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.