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 center dot center dot center dot Br- hydrogen bonds of 2.31(4) angstrom, while the O center dot center dot center dot Br- distances are 3.094(2) angstrom. 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 (la) similarly as in the crystals with the H center dot center dot center dot Br- hydrogen bonds of 1.922 angstrom, while the other (2) is asymmetric and bent, as a result of N+center dot center dot center dot Br- electrostatic attractions with distances between 4.067 and 4.375 angstrom and CH center dot center dot center dot Br- contacts. The FTIR spectrum of I is consistent with the X-ray results. Interpretation of the H-1 and C-13 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 C-13 chemical shifts for the optimized structures of 1a and 2. (C) 2012 Elsevier B.V. All rights reserved.