Spectroscopic investigation of order-disorder phase transition in 4-carboxyanilinium nitrate

Co-crystal 4-carboxyanilinium nitrate (4-CAN) and its deuterated counterpart d4-CAN were studied us -ing vibrational spectroscopy. This study is carried out to understand (i) the intra-and inter-molecular interactions in the co-crystals, 4-CAN in comparison with the parent compounds and (ii) which vibration bands of 4-CAN are affected on structural transition from monoclinic to orthorhombic phases. The Raman and infrared vibrational frequencies of 4-CAN and d4-CAN were assigned using the known frequencies of para-amino benzoic acid (PABA), partially deuterated PABA (dPABA) and HNO3. Close comparison of the spectral features of PABA and 4-CAN suggest a stronger N -H center dot center dot center dot O hydrogen bond interaction and a relatively weaker hydrogen-bond interaction with the carbonyl group in 4-CAN. Temperature dependent IR study of 4-CAN across the order-disorder structural transition indicated that the vibrational bands of -NH3+ and-COOH moieties of 4-CAN are affected due to the changes taking place in hydrogen bond interaction. Present results corroborate well with the reported structural data of 4-CAN. (C) 2021 Elsevier B.V. All rights reserved.