Organic derivatives of the layered perovskite HLaNb2O7·xH2O with polyether chains on the interlayer surface: characterization, intercalation of LiClO4, and ionic conductivity

Abstract

Polyether chains have been successfully grafted onto the interlayer surface of a Dion–Jacobson-type layered perovskite, HLaNb₂O₇·xH₂O, by a reaction between an n-decoxy-derivative of HLaNb₂O₇·xH₂O and CH₃(OCH₂CH₂)_mOH (1 ≤ m ≤ 4). After the reaction, the interlayer distance decreases from 2.73 nm to 1.58 (m = 1), 2.07 (m = 2), 2.28 (m = 3), and 2.69 (m = 4) nm. Solid-state ¹³C CP/MAS NMR spectroscopy indicates that the CH₃(OCH₂CH₂)_mO– groups are bound to the interlayer surface of HLaNb₂O₇·xH₂O. The n-decoxy groups are completely removed by the reaction with CH₃(OCH₂CH₂)_mOH (m = 2 and 3), while a part of the n-decoxy groups remain after the reaction with CH₃(OCH₂CH₂)_mOH (m = 1 and 4). Upon treatment of the CH₃(OCH₂CH₂)_mO-grafted HLaNb₂O₇·xH₂O (m = 2 or 3) with a CH₃(OCH₂CH₂)_mOH solution of LiClO₄, the interlayer distance decreases further to 1.78 (m = 2) and 2.01 (m = 3) nm. Inductively coupled plasma emission spectrometry reveals the presence of lithium (0.22 (m = 2) and 0.24 (m = 3) per [LaNb₂O₇]). The presence of ClO₄⁻ ions is demonstrated by Raman spectroscopy, and the position of the ν₁(A₁) band indicates the presence of isolated ClO₄⁻ ions in the interlayer space. After treatment with a LiClO₄ solution, CH₃(OCH₂CH₂)_mO-grafted HLaNb₂O₇·xH₂O (m = 2 and 3) exhibits ionic conductivity, and no clear temperature dependence is observed.