Experimental and theoretical studies of 1,2-di(3-hydroxypyridinium)-ethylene dibromide

The molecular structure of 1,2-di(3-hydroxypyridinium)-ethylene dibromide (1) has been characterized by single-crystal X-ray diffraction, DFT calculations, FTIR and NMR spectra. The crystals are monoclinic, space group C2/c. The bromide anions are engaged in the H⋯Br− hydrogen bonds of 2.31(4) Å, while the O⋯Br− distances are 3.094(2) Å. The dication and hydrogen-bonded bromide anions are located on the inversion center. From two optimized structures at the B3LYP/6-311++G(d,p) level of theory, one is extended (1a) similarly as in the crystals with the H⋯Br− hydrogen bonds of 1.922 Å, while the other (2) is asymmetric and bent, as a result of N+⋯Br− electrostatic attractions with distances between 4.067 and 4.375 Å and CH⋯Br− contacts. The FTIR spectrum of 1 is consistent with the X-ray results. Interpretation of the 1H and 13C NMR spectra in D2O has been based on 2D experiments. The calculated GIAO/B3LYP/6-311++G(d,p) magnetic isotropic shielding constants have been used to predicted 13C chemical shifts for the optimized structures of 1a and 2.