Ln 2 (OH) 4 SO 4 · n H 2 O (Ln = Pr to Tb; n ∼ 2): A New Family of Layered Rare-Earth Hydroxides Rigidly Pillared by Sulfate Ions
2010; American Chemical Society; Volume: 22; Issue: 21 Linguagem: Inglês
10.1021/cm102236n
ISSN1520-5002
AutoresJianbo Liang, Renzhi Ma, Fengxia Geng, Yasuo Ebina, Takayoshi Sasaki,
Tópico(s)Chemical Synthesis and Characterization
ResumoA new family of layered rare-earth hydroxides rigidly pillared by sulfate ions has been synthesized through homogeneous precipitation of lanthanide sulfate salts driven by hydrolysis of hexamethylenetetramine. Obtained materials were composed of aggregated thin platelet microcrystallites. Chemical analysis indicates that these samples have a general chemical formula of Ln2(OH)4SO4·nH2O (Ln = Pr to Tb; n ∼ 2). The compounds are crystallized in an A-base-centered orthorhombic structure with unit cell dimensions of a ∼ 0.63 nm, b ∼ 1.6−1.7 nm, and c ∼ 0.37 nm. Fourier transform infrared (FT−IR) spectra indicate that sulfate ions are in a trans-bidentate arrangement, which suggests that sulfate ions bridge adjacent rare-earth hydroxide layers through direct coordination to lanthanide cations. The compounds showed two-step weight loss (200−275 °C and ∼350 °C) in the heating process, which can be ascribed to dehydration and dehydroxylation, respectively. Robust lanthanide−sulfate chelate bondings can be inherited even after calcination above 450 °C to yield layered oxysulfates of Ln2O2SO4. Trends in compositional and structural features as well as bonding aspects of hydroxyl groups and sulfate ions across the series, Pr to Tb, are described. Eu and Tb samples exhibited photoluminescence (PL) properties with characteristic red and green emissions, respectively, through both the direct excitation of lanthanide ions themselves and the charge-transfer channels between lanthanide ions and surrounding oxygen atoms.
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