Crystal structure and spectral characterization of La 2 (CO 3 ) 3  ⋅ 5H 2 O – an industrially relevant lanthanide carbonate

The conversion of La 2 O 3 with HCl, subsequent neutralization and precipitation using (NH 4 ) 2 CO 3 in an industrial process leads to the previously unknown La 2 (CO 3 ) 3 ⋅ 5H 2 O. The phase was characterized by X‐ray powder diffraction leading to an averaged crystal structure model, thermal analysis, vibrational and optical spectroscopy. La 2 (CO 3 ) 3 ⋅ 5H 2 O crystallizes in space group Pbca (61) with a =9.0167(4) Å, b =12,842(3) Å, c =9.6331(4) Å and V =1115.4(3) Å 3 . The structure consists of zig zag layers and a highly disordered interlayer space occupied by water molecules and carbonate anions. Partially occupied water‐related oxygen positions theoretically allow for a flexible hydrate water content La 2 (CO 3 ) 3 ⋅ xH 2 O, with x ranging from 1.5 to 5.0. Although a strong structural relationship between La 2 (CO 3 ) 3 ⋅ 5H 2 O and La 2 (CO 3 ) 3 ⋅ 8H 2 O and similar substance properties were found, the title compound cannot be obtained by partial dehydration of the octahydrate. Instead, both lanthanum carbonate hydrates transform into strongly disordered La 2 (CO 3 ) 3 in a one‐step dehydration process.