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

Abstract

The crystals of bis(homarine)hydrogen perchlorate, (HOM) 2H·ClO 4, ( 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 ClO 4 - anion additionally interacts electrostatically with the positively charged nitrogen atoms of the neighbouring HOM molecules. The most stable conformer of (HOM) 2H·ClO 4 ( 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·ClO 4 shows a broad and intense absorption in the 1500–400 cm −1 region, typical of short hydrogen bonds.