Observation of Deuteration Effect in Co-Crystal System: Hexamethylenetetraminium 3,5-Dinitrobenzoate Hemideuterated Water

Variable-temperature single-crystal X-ray diffraction, DSC (differential scanning calorimetry), and dielectric measurements show that the co-crystal system (D-HMTA)(DNBA)(0.5D2O) (1) (HMTA = hexamethylenetetramine, H-DNBA = 3,5-dinitrobenzoic acid) easily undergoes phase transitions because the H-bonds (or D-bonds) in the high-temperature phase are on the average weaker than those in the low-temperature phase; the high-temperature phase also exhibits striking isotopic effects.