Hydrothermal Syntheses, Structures, and Characterizations of Two Lanthanide Sulfate Hydrates Materials, La₂(SO₄)₃·H₂O and Eu₂(SO₄)₃·4H₂O

Abstract

Two-or three-dimensional framework materials containing rich structural diversities are of continuous interest attributable to their technologically important properties and potential applications such as catalysis, ion-exchange, adsorption, intercalation, and radioactive waste remediation. [1][2][3][4] Materials showing these functional features are normally composed of structurally versatile cations. Heavier metal cations with larger coordination spheres and cations exhibiting ability to accommodate other polyhedral units could be excellent candidates for materials with rich structural variations. Among many, lanthanide cations have been used widely, since they could create higher coordination numbers as well as easily adopt other metal polyhedra to generate the full range of topological diversity in the frameworks. [5][6][7] Meanwhile, one of the most effective synthetic methods for the preparations of these versatile framework materials is a hydrothermal (or solvothermal) reaction technique. [8][9][10][11][12][13] In this synthetic method, mineralizers such as acids or bases are introduced to increase the solubility and reactivity of the reagents.14,15 And also, organic or inorganic templates are used to direct the framework structures and the subsequent physical properties of the products. 1,8,9 Thus, we have utilized hydrothermal reactions with two lanthanide cations (La 3+ and Eu 3+ ) and sulfate anions to prepare higher dimensional framework materials. A number of lanthanide sulfate hydrate materials with general formula of Ln2(SO4)3·xH2O have been reported (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb).16-39 The number of hydration, x varies from 1 to 9 for most of lanthanide cations. Until now, approximately nine different phases including one orthorhombic, two triclinic, five monoclinic, and one hexagonal structure have been reported. However, any systematic approaches to understand the factors affecting on the formation of different polymorphs are rarely observed. It would be very important to understand the relationships between the reaction conditions employed and the product obtained in any hydrothermal reaction. In this paper, we report on the hydrothermal syntheses, full structural descriptions, and characterizations of two lanthanide sulfate hydrate materials, La2(SO4)3·H2O and Eu2(SO4)3·4H2O. With the lanthanum (III) cation, a systematic synthetic study to reveal the origin of the formation of different polymorphs with different hydration number is also discussed. Experimental SectionSynthesis. La (NO3) . The products were recovered by filtration and washed with water. Pure crystals, the only product from each reaction, of La2(SO4)3·H2O and Eu2(SO4)3·4H2O were obtained in 80 ~ 90% yield, on the basis of the corresponding lanthanide nitrates. The crystal structure of La2(SO4)3·H2O has been reported recently. 35 The material has been prepared at 180 o C for 7 days using LaCl3·2H2O and sulfuric acid. And also, the authors argued that 1,2-diaminopropane is necessary as a structure direc...

Crystal Structure, Vibrational, Spectroscopic and Thermochemical Properties of Double Sulfate Crystalline Hydrate [CsEu(H2O)3(SO4)2]·H2O and Its Thermal Dehydration Product CsEu(SO4)2

“…For this reason, in complex compounds, it is difficult to clearly determine the relation between the coordination and spectroscopic parameters of Eu 3+ ions in the host lattice. In such a situation, the compounds with a stoichiometric content of europium ions have attracted the increasing attention of researchers [37,38,[47][48][49][50][51][52][53]. Self-activated phosphors are characterized by an almost complete absence of structural defects, and the precise determination of the crystal structure makes it possible to evaluate the relations between the Eu 3+ ion coordination in the lattice and spectroscopic characteristics of the compound.…”

“…Simple europium stoichiometric compounds with tetrahedral MO 4 units, where M = Mo, W and S, were thoroughly studied and their applicability as highly efficient polyfunctional materials was shown [54][55][56][57][58][59][60][61][62][63][64][65][66][67]. At the same time, the properties of complex compounds of monovalent cations and rare-earth elements with tetrahedral anions are presented quite sporadically in the literature [37,[48][49][50][51]53,[68][69][70][71][72]. The structures and some properties of several double molybdates and tungstates with general composition AEu(MO 4 ) 2 (A = Li, Na, K, Cs, Rb, Ag + ; M = Mo, W) were investigated in the past and the examples of such contributions can be found elsewhere [72][73][74][75][76].…”

Exploration of structural, thermal and spectroscopic properties of self-activated sulfate Eu2(SO4)3 with isolated SO4 groups

“…In the past, several studies were devoted to the synthesis and characterization of europium (III) sulfate, and it was shown that the preparation of Eu2(SO4)3 is a nontrivial task because of high a tendency to hydration [13,[35][36][37][38]. The available structural properties of the presently known Eu 3+ sulfate hydrates are listed in Table S2 [20,35,[39][40][41][42][43]. Nevertheless, to the best of our knowledge, the crystal structure and basic physical properties of anhydrous Eu2(SO4)3 are still unknown.…”

“…In both tetrahedra the O-S-O angles are different from the ideal tetrahedral angle and vary within 102-121°, and that leads to a significant deforming of tetrahedra. The sulfate tetrahedra in europium (III) sulfate have much more deformation in comparison with the tetrahedra in the structures of europium sulfates crystallohydrates[20,35,[39][40][41][42][43], apparently, because of a higher anhydrous sulfate structure rigidity.…”

A Raman spectroscopic investigation of speciation in La2(SO4)3(aq)

“…Lanthanum sulfate enneahydrate, La 2 (SO 4 ) 3 $9H 2 O, is the most common hydrate of lanthanum sulfate, La 2 (SO 4 ) 3 $nH 2 O (n ¼ 1-9) [1][2][3] and is the only stable hydrate in contact with its solution between 0 and 100 . La 2 (SO 4 ) 3 is sparingly soluble at room temperature and the solubility diminishes with temperature.…”