X Factor in the Structure and Anion Exchange of Layered Yttrium Hydroxides

The anion-exchangeable family of layered rare-earth hydroxides RE2(OH)(5)X center dot nH(2)O (LREH-X, RE = rare-earth elements such as Y, X- = monovalent anions, n approximate to 1.5) exhibits considerable potential in various applications. However, their structures remain controversial or even unresolved. Herein, a comprehensive study involving 1D and 2D Y-89 solid-state NMR spectroscopy, powder X-ray/neutron diffraction, and periodic DFT calculations was conducted to solve the structure of LYH-X (X- = Cl-, Br-, NO3-), one of the most extensively used and studied subjects of the LREH-X family. The anion-exchange behaviors were then investigated, and the results clearly demonstrate strong influences of X- on the structure and anion exchange: first, the structure of LYH-Cl is orthorhombic P2(1)2(1)2, whereas LYH-Br and LYH-NO3 are monoclinic P2(1) structures; second, the conversion from the high-symmetry P2(1)2(1)2 phase to the low-symmetry P2(1) phase can be conducted quite well via anion exchange, but not vice versa; finally, the foreign anions site-specifically interact with host layers. Such strong influences are the unique characteristics of LYH-X and thus should be considered in future studies and applications of these materials.

Automated summary

The structure and anion exchange behaviors of LYH-X are strongly influenced by X-, resulting in different structures and conversion between them; foreign anions interact specifically with host layers. These characteristics should be taken into consideration in future studies and applications.