Two-step crystallization of a phase-pure Ln2(OH)5NO3·nH2O layered compound for the smallest Ln ions of Tm, Yb and Lu, anion exchange, and exfoliation

Abstract

Crystallization of the Ln₂(OH)₅NO₃·nH₂O layered hydroxide (LLnH) is the most difficult for the three smallest lanthanide ions of Tm, Yb and Lu. By applying a novel two-step crystallization technique, which involves chemical precipitation at a freezing-temperature of ∼4 °C and subsequent Ostwald ripening at 50 °C for Tm and Yb and 65 °C for Lu, the three compounds have been obtained in a phase-pure form without the use of any mineralizer. The resulting LTmH and LYbH (n ∼ 1.5) were shown to accommodate free NO₃⁻ anions in the interlayer gallery, which are readily exchangeable by DS⁻ (C₁₂H₂₅OSO₃⁻). Delamination of the DS⁻ derivatives in formamide produced micron-sized nanosheets of ∼1.7 nm thick. A similar anion exchange was found to hardly proceed for LLuH even at 65 °C, owing to the direct coordination of the interlayer NO₃⁻ with the Lu³⁺ center.