Effet isotopique 6Li7Li dans le spectre infra-rouge de composes inorganiques du lithium-I. Carbonate, chromo-ferrite, tungstate, molybdate et nitrate de lithium

The infra-red spectra of crystalline Li2CO3, LiFeCr4O8, Li2WO4, Li2MoO4 and LiNO3, and of the isotopic species with 6Li have been studied in the 1600-290 cm-1 region. In the first four compounds, bands related to the stretching frequency of LiO4 tetrahedra are easily identified by a 6Li7Li isotopic shift of 20-30 cm-1, an amount in agreement with a theoretical estimation. Despite the diversity in chemical composition and crystal structure of the compounds studied, these LiO4 bands are observed in a fairly well defined region, namely 500-400 cm-1. No LiO bands, however, are found in the spectrum of LiNO3, the structure of which contains LiO6 octahedra (and no LiO4 tetrahedra), and it is inferred that the stretching frequencies of LiO6 octahedra should be located below 300 cm-1. This difference in the spectroscopic behaviour of LiO4 tetrahedra and LiO6 octahedra may be used for determining the co-ordination number of lithium in compounds of unknown structure. © 1965.