Spectre infra-rouge et structure des composés GaPO4·2H2O et GaAsO4·2H2O

The compounds GaPO4·2H2O and GaAsO4·2H2O have been synthesized and investigated by i.r. absorption spectroscopy (4000-200 cm-1) X-ray diffractometry and thermal gravimetric analysis. The i.r. spectrum is characterized by the lack of absorption bands in the 1600-1700 cm-1 region, the occurrence of a very diffuse absorption near 1500 cm-1 and 3100 cm-1, and a narrow band between 3500 and 3600 cm-1. This rather peculiar pattern had already been observed in other compounds of similar chemical composition and is interpreted as arising from the presence, in the crystals, of OH- and H3O+ ions instead of water molecules. This unexpected type of structure is supported by OH-OD exchange reactions; the structural analogies within a series of compounds of the AXO4·2H2O type are confirmed by X-ray diffractometry. © 1969.