Salts of 4-(2,4,6-triphenyl-1-pyridinio)phenolate with p-toluenesulfonic acid in molar ratio 1 : 1 and 2 : 1 - Crystal and molecular structure

Two new salts of 4-(2,4,6-Triphenyl-1-pyridinio)phenolate with p-toluenesul fonic acid in molar ratio 2:1 ("red salt") and 1:1 ("colourless salt") were synthesised. The solvatochromic effect, H-1 NMR spectra and crystal struct ure of the salts were investigated. In the crystalline "red salt" two molec ules of the betaine dye are joined by a strong, asymmetric hydrogen bond co ntrary to previous suggestions. Similar behaviour is observed in polar solv ents, but the hydrogen bond is symmetric. In solvents of low polarity an ad ditional intermolecular charge-transfer interaction is possible.