Synthesis, characterization and properties of microporous lanthanide silicates: K 8 Ln 3 Si 12 O 32 NO 3 ·H 2 O (Ln = Eu, Tb, Gd, Sm)

Abstract

A family of microporous lanthanide silicates, K 8 Ln 3 Si 12 O 32 NO 3 ·H 2 O (denoted LnSiO-CJ3, Ln = Eu, Tb, Gd, Sm), was synthesized under mild hydrothermal conditions at 503 K. The X-ray powder diffraction patterns of these compounds reveal that they are isostructural. The structure of EuSiO-CJ3 was determined by single-crystal X-ray diffraction analysis. It crystallizes in triclinic space group P-1 (No. 2) with a = 11.599(2) Å, b = 12.225(2) Å, c = 13.829(3) Å, α = 112.99(3)°, β = 92.05(3)°, γ = 90.57(3)°. The structure is based on [Si 3 O 8 ] n 4n- layers with 6-, 8-, 12-rings that are connected by EuO 6 octahedra to form a 3-D framework with 8-ring channels along the [001] direction. Charge neutrality is achieved by the K + and NO 3 - ions located in the channels. The framework of EuSiO-CJ3 shows good thermal stability, which can be stable up to 1273 K. Ion-exchange capacity of EuSiO-CJ3 was investigated by the exchange of NO 3 - ions with halide ions (F -, Cl -, Br -). The peaks in the emission spectra of LnSiO-CJ3 (Ln = Eu, Tb) belong to the characteristic transitions of Ln 3+ (Ln = Eu, Tb) respectively. The lifetime measurements of LnSiO-CJ3 (Ln = Eu, Tb) suggest the presence of three Ln 3+ (Ln = Eu, Tb) environments, which are consistent with the crystallographic results. © 2009 Elsevier Masson SAS. All rights reserved.