Vibrational spectra and structure of crystalline dipicolinic acid and calcium dipicolinate trihydrate

Abstract

The i.r. (4000-30 cm-1) and Raman (4000-20 cm-1) spectra of 2,6-pyridinedicarboxylic acid C5H3N(COOH)2, C5H3N(COOD)2, 2,6-pyridine-4-d1 dicarboxylic acid and calcium dipicolinate trihydrate (the equimolar salt of calcium and 2,6-pyridinedicarboxylic acid) at 100 K have been investigated. A tentative assignment is given by referring to the isotopic frequency shifts and group frequency considerations as well as to depolarization ratios. Thirty-four internal vibrations from the 39 expected modes have been observed for the crystalline dipicolinate ion, the relevant molecular point group being C 2ν. Cyclic centrosymmetric dimeric structures involving the carboxyl groups in the acid are proposed to explain the spectral features of this compound. © 1980.