Molecular structure of bis(pyridiniumvalerate) hydrogen perchlorate studied by X-ray diffraction, FTIR spectroscopy, PM3 and SAM1 calculations

Abstract

In the crystal structure of bis(pyridiniumvalerate) hydrogen perchlorate, determined by X-ray diffraction, a pair of pyridiniumvalerate molecules form a linear cation bridged by a very strong hydrogen bond of length 2.458(9)Å. The positively charged N atoms of the cation interact electrostatically with the carboxylate groups from neighbouring molecules and also with the disordered perchlorate anions. The FTIR spectrum of the compound shows an intense broad (continuum) absorption below 2000cm−1, typical of short-strong hydrogen bonds, and a single νCO band at 1706cm−1. The PM3 and SAM1 calculations predict a non-linear structure of the isolated cation due to intramolecular electrostatic interactions of the N+ atoms with COO− groups. The effect of the number of CH2 groups on the conformation and geometry of the COO group in dimeric cation of pyridine betaines is discussed.