Redetermination of dicerium(III) tris(sulfate) tetrahydrate

Ce2(SO4)3(H2O)4 was obtained hydrothermally from an aqueous solution of cerium(III) oxide, trimethylamine and sulfuric acid. The precision of the structure determination has been significantly improved compared with the previous result [Dereigne (1972 ▶). Bull. Soc. Fr. Mineral. Cristallogr. 95, 269–280]. The coordination about the two Ce atoms is achieved by seven and six bridging O atoms from sulfate anions. Each S atom makes four S—O—Ce linkages through bridging O atoms. The coordination sphere of each Ce is completed by two water molecules, which act as terminal ligands.


S1. Comment
Over the past decades, the design and synthesis of new three-dimensional solid state materials have received great attention, due to their functional applications in catalysis and optical device. As the building elements germanium has been choosen to synthesize new porous materials (Li et al., 1998;Plévert et al., 2001;Xu, Cheng & You, 2006;Xu, Ding et al., 2006). In the last few years, an important advance in three dimensional inorganic materials has been achieved by study of lanthanide sulfates frameworks (Zhang et al.,2004;Yuan et al., 2004;Xu, Ding et al., 2006;Doran et al., 2002).
In this work, we synthesized the title compound, Cerium(3+) sulfate tetrahydrate, which features a three-dimensional framework. The structure of title compound had been reported previously (Dereigne et al., 1972), however, the precision of redetermination is much improved.
As isostructure with La 2 (SO 4 ) 3 (H 2 O) 4 and Nd 2 (SO 4 ) 3 (H 2 O) 4 (Shi, 1987), the framework of title compound is constructed from CeO 9 and CeO 8 polyhedra and SO 4 tetrahedra. As shown in Fig. 1 and 2, the asymmetric unit contains two Ce 3+ , three SO 4 2groups and four water molecules, all of which belong to the inorganic framework. The coordination about Ce1 and Ce2, respectively, is achieved by bridging oxygen atoms from sulfate anions. Each S atom makes four S-O-Ce linkages through bridging O atoms. The coordination sphere of each Ce is completed by two water molecules, which act as terminal ligands of Ce^3+^.
The Ce atom has the typical geometrical parameters, with Ce-O distances of 2.354 (3)-2.710 (3)Å (Table 1). The O-Ce-O angles are between 59.28 (14) and 139.03 (14)°. These bond distances and bond angles are in agreement with those found in similar rare-earth compounds (Zhang et al.,2004;Yuan et al., 2004). The geometry of the sulfate ions is unexceptional. Fig. 3 shows the three-dimensional arrangement in the unit cell, displaying the way the different CeO 9 polyhydra are connected by bridging sulfates.

S2. Experimental
Colorless block-shaped crystals were synthesized hydrothermally from a mixture of CeCl 3 .6H 2 O, H 2 SO 4 (98%), H 2 O and trimethylamine(25%). All the chemicals are purchased from Shanghai Chemical Reagent Factory. In a typical synthesis, CeCl 3 .6H 2 O(0.2993 g) was dissolved in a mixture of trimethylamine (25%, 0.7893 g) and of water (1 ml) followed by the addition of H 2 SO 4 (98%) (0.3528 g) with constant stirring. Finally, the mixture was kept in a 25 ml Teflon-lined steel autoclave at 180 °C for 6 days. The autoclave was slowly cooled to room temperature, and then the product was filtered, washed with distilled water, and dried at room temperature. Colorless block-shaped crystals of the title compound were obtained.

S3. Refinement
The highest peak in the difference map is 1.12 e/Å 3 , and 1.26 (2) Å from Ce 2 , while the minimum peak is -2.16 (2) Å from Ce 1 . 5. The H atoms of water were located from different map, and the O-H distances are restrained to 0.85 (2) Å.  The coordination of Ce1 for title compound. Displacement ellipsoids at the 70% probability level. Symmetry codes as in  The coordination of Ce2 for title compound. Displacement ellipsoids at the 70% probability level. Symmetry codes as in Table 1.

Figure 3
The crystal packing in the unit cell of Ce(SO 4 )(OH). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.12 e Å −3 Δρ min = −2.16 e Å −3 Extinction correction: SHELXL, Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0953 (15) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.