FT-IR and FT-Raman study of selected pyridinephosphonocarboxylic acids

In this work we present FT-IR and FT-Raman spectra of three acids: pyridine-2-phosphono-4-carboxylic (MCI), pyridine-2-phosphono-5-carboxylic (MC2), and pyridine-2-phosphono-6-carboxylic (MC3) that possess potential neuroactive abilities. Their molecular structures and vibrational frequencies are calculated with ab initio Hartree-Fock and density functional theory methods (DFT) using the local (SVWN) and hybrid (B3LYP, B3PW91) exchange functionals. Here we discuss and compare differences in geometrical structures and vibrational patterns obtained by ab initio and DFT methods used in this work. The best agreement between the experimental and calculated spectra was obtained at the B3PW91/6-31G** level. Assignments of Raman and IR bands for all studied acids are made on the basis of potential energy distribution (PED). We also show how the arrangements of phosphonato and carboxylic substituents on the pyridine ring change the vibrational structure of pyridine. (C) 2003 Elsevier Science B.V. All rights reserved.