Rare Earth Oxohydroxyglycinates: The Possible Missing Link Between Rare Earth Oxides and Hydroxides

Rare earth oxides (RE 2 O 3 ) were found to react with glycine in an aqueous medium at rather low temperatures (60°С–120°С), forming rare earth oxohydroxyglycinates, RE 2 O(OH) 3 (NH 2 CH 2 COO)·H 2 O, with a previously unknown crystal structure. The structure of the europium oxohydroxyglycinate was determined using powder X‐ray diffraction. Its layered structure and ability for anion exchange under mild conditions, namely the exchange of glycinate ions for dodecyl sulfate ions, makes it similar to layered rare earth hydroxides (LREHs). However, according to the crystal structure and extended X‐ray absorption fine structure data, in europium oxohydroxyglycinate, europium cations possess low coordination numbers, 6 and 7, which are very untypical for LREHs but typical for rare earth oxides. This suggests that rare earth oxohydroxyglycinates should be placed in a separate group of layered rare earth compounds that are similar to both LREHs and RE 2 O 3 . Interestingly, under similar synthetic conditions, the closest analogs of glycine, namely alanine, and phenylalanine, do not react with rare earth oxides, which enables the assumption that the formation of rare earth oxohydroxyglycinates proceeds through the topotactic reaction.