Layered rare-earth hydroxides: crystal engineering toward functional nanosheets

Anion-exchangeable layered host compounds have attracted significant interest in many areas of chemistry. In particular, disintegrating the crystalline layered solids into single layers provides molecularly thin 2D materials as graphene relatives. This review addresses a newly emerging layered host, layered rare-earth (RE) hydroxides, in which anion exchangeability is paired with the intriguing properties of RE elements. The evolution of this class of layered materials exemplifies the concept of crystal engineering, whereby a cationic 2D lattice is derived from the crystalline framework of RE(OH)3 via dimensional reduction and topology engineering. Subsequent chemical exfoliation leads to RE-based hydroxide nanosheets. These nanosheets are employed as LEGO-like building blocks to construct artificial hierarchical structures, which offer promising opportunities for realizing sophisticated functionalities.