Investigation of the Structural Properties of an Extended Series of Lanthanide Bis-hydroxychlorides Ln(OH)₂Cl (Ln = Nd−Lu, except Pm and Sm)

Abstract

The trivalent lanthanide bis-hydroxychloride compounds, Ln(OH)(2)Cl, (Ln = Nd through Lu, with the exception of Pm and Sm) have been prepared by hydrothermal synthesis starting with LnCl(3).nH(2)O. These compounds were synthesized at temperatures not exceeding the melting point of the Teflon liners in the Parr autoclaves ( approximately 220 degrees C). The compounds obtained were characterized by single crystal X-ray diffraction analysis, diffuse reflectance, FT-IR, and FT-Raman spectroscopies. Most of the lanthanide(III) bis-hydroxychlorides are isostructural and generally crystallize in the monoclinic space group P2(1)/m. The bis-hydroxychlorides of the heavier lanthanide(III) atoms with smaller ionic radii also crystallize in the orthorhombic crystal system. Apparently hydrogen bonds between the OH groups and the Cl atoms connect the layers in the "c" direction. These H-bonds seem to be the driving force for the angle beta of the monoclinic complexes to decrease with decreasing ionic radius of the Ln(III) ion and also for tying the layers together more strongly. As a result of this behavior, the structure of the heavier 4f analogues significantly resembles that of their orthorhombic counterparts. The heavier lanthanide bis-hydroxychlorides preferentially crystallize in the orthorhombic modification. The IR absorbance and Raman frequencies of the hydroxide ligands correlate as a function of the central lanthanide(III) ionic radius. This observation is corroborated by X-ray diffraction (XRD) structural data. These compounds are quite insoluble in near-neutral and basic aqueous solutions, but soluble in acidic solutions. It is expected that the analogue actinide bis-hydroxychlorides exhibit similar behavior and that this may have important implications in the immobilization and safe disposal of nuclear waste.

Preparation of CeSiO4 from aqueous precursors under soft hydrothermal conditions

“…Ce(OH) 2 Cl is isostructural to Ln(OH) 2 Cl phases which were formed under hydrothermal conditions in experimental conditions close to those developed in this study. 57,58 Due to its high solubility in nitric acid, a washing step of 10 minutes with 1 M nitric acid after the synthesis allowed to dissolve specifically the Ce(OH) 2 Cl phase leading to a CeSiO 4 and CeO 2 mixture (Figure 9). The direct comparison of the results obtained in nitric and hydrochloric media showed that oxidation of cerium(III) to cerium(IV) necessary to form CeSiO 4 was not only due to the presence of nitrate ions.…”

Heat-Induced Transformation of Luminescent, Size Tuneable, Anisotropic Eu:Lu(OH)2Cl Microparticles to Micro-Structurally Controlled Eu:Lu2O3 Microplatelets

“…Monoclinic lutetium dihydroxychloride (Lu(OH) 2 Cl) anisotropic micro-and nanoparticles doped with 3 mol % were synthesised by microwave assisted non-aqueous solvothermal reactions using lutetium chloride as precursor in benzyl alcohol as a solvent. XRD analysis revealed the monoclininc crystal structure of the products, irrespective of the synthetic conditions chosen (Figure 1d) [17,22]. The product stoichiometry was further confirmed by microelemental analysis on the obtained powders, which showed a ratio of carbon (0.09), chlorine (1.0) and hydrogen (2.4) with respect to Lutetium (1.0).…”

“…All the Lu(OH) 2 Cl particles in this work exhibited an anisotropic, hexagonal-shaped elongated platelet morphology which was retained in both polar and unpolar solvents (Figure 1, Figures S1 and S2). This is likely due to the anisotropic unit cell of monoclinic Lu(OH) 2 Cl, which possesses three distinct crystallographic axes a, b and c along which different crystal growth rates may be expected, possibly resulting in the observed morphologies [22].…”

“…TGA revealed three regions of weight loss upon heating up to 1000 °C, the different stages of the heat induced transformation were labelled with different colours, orange (<400 °C), green (400-650 °C) and red (>650 °C) (Figure 2a). XRD heated in situ (Figure 2b) showed that the initial monoclinic Lu(OH)2Cl degraded to an intermediate product which can be at least partially associated with LuOCl before it fully turned into cubic Lu2O3 [22,25]. The last stage above 650 °C corresponded to the coalescence of the Lu2O3 crystallites.…”

(Acetato-κ2O,O′)dihydroxidoytterbium(III) hemihydrate

“…The creation of open frameworks has increased considerably over the last decade due to their widespread potential applications in areas such as electronics (Fé rey et al, 2007), drug delivery (Horcajada et al, 2008;Vallet-Regi et al, 2007) and catalytic systems (Gá ndara et al, 2008;Mueller et al, 2008). We recently discussed the structural trends within an extended series of lanthanide bis(hydroxychlorides) [Ln(OH) 2 Cl; Zehnder et al, 2010], which represent purely inorganic threedimensional open frameworks, as they may have potential implications for the long-term isolation and storage of radioactive waste materials. Other purely inorganic three-dimensional networks, assembling to various forms of zeolite structures, have become very useful as molecular sieves (Meier et al, 1996).…”