Fourier transform IR spectra of the propionates of La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y were studied. The principal IR absorption bands were assigned for 100-1800 cm-1. The strong absorption bands near 316-349 cm-1 were believed to be Ln-O stretching bands. Mid-IR spectra of rare earth propionates can be divided into 2 types, indicating that there are 2 different carboxylate coordinate forms. For 11 of the 13 rare earth propionates (except Yb, Lu), the carboxylate coordination had the chelating bidentate form, whereas at least, 1 of the 3 carboxylate groups had the form of chelation-bridging tridentate for Yb and Lu propionates, i.e. 1 of the carboxyl O was shared between 2 adjacent metal ions. The Ln-O bond of rare earth propionate is principally ionic.

Key words: METHYLACETIC ACID P, INFRARED SPECTROPHOTOMETRY, LANTHANUM COMPOUNDS, NEODYMIUM COMPOUNDS, RARE EARTH COMPOUNDS, PRASEODYMIUM COMPOUNDS, YTTRIUM COMPOUNDS, ERBIUM COMPOUNDS, GADOLINIUM COMPOUND, THULIUM COMPOUNDS