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)(2)H center dot ClO4, (1) are orthorhombic, space group C2/c, with a pair of HOM molecules bridged by a symmetrical O center dot H center dot O hydrogen bond of 2.480(3) angstrom. In the homoconjugated cation, (HOM center dot H center dot HOM)(+), the H-bonded proton is in centre of inversion. The COO groups are inclined by 29.98(18)degrees 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)(2)H center dot ClO4 (2) and four homoconjugated cations, (HOM)(2)H, (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 center dot H center dot HOM unit. The FTIR spectrum of the (HOM)(2)H center dot ClO4 shows a broad and intense absorption in the 1500-400 cm(-1) region, typical of short hydrogen bonds. (C) 2006 Elsevier B.V. All rights reserved.