Crystal and molecular structure, hydrogen bonding and electrostatic interactions of bis(homarine) hydrogen perchlorate studied by X-ray diffraction, DFT calculations, FTIR and Raman spectroscopies

The crystals of bis(homarine)hydrogen perchlorate, (HOM)2H·ClO4, (1) are orthorhombic, space group C2/c, with a pair of HOM molecules bridged by a symmetrical O·H·O hydrogen bond of 2.480(3) Å. In the homoconjugated cation, (HOM·H·HOM)+, the H-bonded proton is in centre of inversion. The COO groups are inclined by 29.98(18)° to the plane of the pyridine rings, but pyridine rings are coplanar. The ClO4- anion additionally interacts electrostatically with the positively charged nitrogen atoms of the neighbouring HOM molecules. The most stable conformer of (HOM)2H·ClO4 (2) and four homoconjugated cations, (HOM)2H, (3–6) were analysed by the B3LYP/6-31G(d,p) calculations in order to determine the influence of the anion on the hydrogen bonds in the HOM·H·HOM unit. The FTIR spectrum of the (HOM)2H·ClO4 shows a broad and intense absorption in the 1500–400 cm−1 region, typical of short hydrogen bonds.