RE(SO4)[B(OH)4](H2O), RE(SO4)[B(OH)4](H2O)2, and RE(SO4)[B(OH)4](H2O)·H2O: Rare-Earth Borate-Sulfates Featuring Three Types of Layered Structures.

Abstract

Using hydrothermal reactions, three series of rare-earth borate-sulfates, namely, RE(SO4)[B(OH)4](H2O) (RE = La (1), Sm (2), Eu (3)), RE(SO4)[B(OH)4](H2O)2 (RE = Pr (4), Nd (5), Sm (6), Eu (7), Gd (8)), and RE(SO4)[B(OH)4](H2O)·H2O (RE = Tb (9), Dy (10), Ho (11), Er (12), Tm (13), Yb (14), Lu (15), Y (16)), have been synthesized, which represent the first rare-earth borate-sulfate mixed-anion compounds. All these compounds possess the same fundamental building anionic units of SO4 and B(OH)4 tetrahedra; however, they exhibit three different types of two-dimensional (2D) layered structures composed of 1D RE-B-O and RE-S-O chains. The rare-earth borate chains are similar in all compounds, while the rare-earth sulfate chains differ in each type of compound due to the various coordination modes of sulfate groups. On the basis of the measured UV-vis diffuse reflectance spectra, the optical band gaps of compounds 2, 3, 6, and 7 are estimated to be 4.66, 4.53, 4.62, and 4.50 eV, respectively. Luminescence studies show that compounds 2, 3, 6, and 7 exhibit strong emission in the orange or red regions. Furthermore, thermal analysis and magnetic susceptibility measurements for these four representative compounds have also been performed.