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

In the crystal structure of bis(pyridiniumvalerate) hydrogen perchlorate, d etermined 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) Angstrom. The positively charged N atoms of the cation interact electrostat ically with the carboxylate groups from neighbouring molecules and also wit h the disordered perchlorate anions. The FTIR spectrum of the compound show s an intense broad (continuum) absorption below 2000 cm(-1), typical of sho rt-strong hydrogen bonds, and a single nuC=O band at 1706 cm(-1). The PM3 a nd 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 geom etry of the COO- group in dimeric cation of pyridine betaines is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.