Vibrational spectra, normal coordinate analysis, and hydrogen bond investigation of pyridinium perchlorate

Abstract

The IR and Raman spectra of pyridine perchlorate salt (PyHClO4) have been recorded in the 4000–300 and 3200–200cm−1 regions, respectively. The structure and vibrational spectra of pyridine salt have been investigated by means of ab initio and density functional theory (DFT) calculations. To examine the efficiency of basis sets in predicting the vibrational spectra of ClO4−1 ion, several basis sets were used with the B3LYP and B2PLYP levels of theory. It was shown that the 6-311(3df) basis set gives reasonably vibrational wavenumbers for simulation of perchlorate ion experimental vibrational wavenumbers. Therefore, the B3LYP/6-311G(3df) level was used to calculate the vibrational spectra of pyridine perchlorate salt in CH3CN solution. For comparison, the vibrational wavenumbers were also calculated at the B3LYP/aug-cc-pVTZ level. The geometry of PyHClO4 was calculated in the gas phase as well as in solutions, using SCRF-PCM method. According to these calculations, the structure and hydrogen bonding in PyHClO4 is highly affected by media. Two hydrogen bonding systems between ClO4−1 and pyridinium ions were recognized. The nature of these hydrogen bonds is theoretically investigated by using atoms in molecule (AIM) method and natural bond orbital (NBO) analysis. A normal coordinate analysis was performed by using the internal coordinates calculated at the B3LYP/6-311G(3df,p) level for the vibrational normal modes of the titled compound.