N-H...Br, Br...π and π...π interactions toward self-assembly of the cytosine hydrobromide: crystal structure, infrared spectroscopy and thermal behavior

Abstract

The cytosine hydrobromide (CytHBr) was obtained and studied by single-crystal X-ray diffraction, FT-IR spectroscopy and thermal analysis. This salt crystallizes in the P'2IND.1/n space group with one ionic-pair CytH+Br in the asymmetric unit. The CytHBr compound forms centrosymmetric R'IND.2POT.2' (8) dimers, linking the cationic units (CytH+) in infinite strands of ionic pairs arranged in zigzag layers, connected by π...π and π...Br- interactions. Also, the Hirshfeld Surface (HS) and fingerprint plots were used to explore the H...Br, C...H, C...C, C...N, C...O and C...Br intermolecular contacts. The molecular assembly of CytHBr is similar compared with the cytosine hydrochloride salt (CytHCl). As a result, the FT-IR spectrum of the CytHBr is similar to that one reported for the CytHCl. On the other hand, small shifts are observed comparing with the pure cytosine (Cyt) spectrum. The CytHBr was also studied by thermal analysis (DSC and TGA), supported by Hot Stage and Optical Microscopy (HSOM) technique, confirming the high-quality of the crystalline modification.