Inorg. Chem. 2004, 43, 5954−5960
New Aluminate with a Tetrahedral Structure Closely Related to the C84 Fullerene S. Boudin,* B. Mellenne, R. Retoux, M. Hervieu, and B. Raveau Laboratoire CRISMAT, UMR CNRS ENSICAEN 6508, 6 bd Mare´ chal Juin, 14050 CAEN Cedex 4, France Received March 12, 2004
A new aluminate Sr33Bi24+δAl48O141+3δ/2, having an F4h3m cubic structure (a ) 25.090 Å, Z ) 4) and forming a close packed face centered cubic array of “Al84” fullerene geometry, has been discovered. This original structure consists of corner-sharing AlO4 tetrahedra forming “Al84O106” cubic units whose assemblage delimits five types of cages, three of them being empty, one being occupied by strontium, and the fifth one forming the huge spheric fullerene-type cavity. In the latter, strontium, oxygen, and bismuth ions form concentric spheres, with an onionskin-like configuration. The latter ions are disposed into a compact “Bi16O52-n0n” anion whose the exceptional geometry is characterized by a strong stereoactivity of the 6s2 lone pair of Bi3+.
Aluminum, owing to its great ability to adopt the tetrahedral coordination, is often associated with silicon to form tridimensional tetrahedral frameworks characterized by large cages and tunnels such as zeolites and ultramarines,1-4 which have been extensively studied for their ion exchange properties, their application as molecular sieves, and their catalytic properties. Pure aluminates forming such 3D-frameworks with large cages have also been synthesized but are much less numerous. It is the case of the sodalite family of generic formulation A8Al12O24(MOn) with A ) Ca, Sr, Ln and M ) Cr, Mo, W, Pb.5-13 The introduction of bismuth cations in an “Al-O” framework is also possible, as shown for instance by the bismuth-strontium aluminate Sr6Bi2O3(AlO2)1214 * To whom correspondence should be addressed. E-mail: boudin@ crismat.ismra.fr. (1) Wells, A. F. Structural Inorganic Chemistry; Oxford University Press: Oxford, 1993. (2) Non-stoichiometric Compounds; Mandelcorn, L., Ed.; Academic Press: New York, 1964. (3) Cheetham, A. K.; Ferey, G.; Loiseau, T. Angew. Chem., Int. Ed. 1999, 38, 3268. (4) Zones, S. I.; Davis, M. E. Curr. Opin. Solid State Mater. Sci. 1996, 1, 107. (5) Depmeier, W.; Schmid, H.; Setter, N.; Werk, M. L. Acta Crystallogr., Sect. C 1987, 43, 2251. (6) Van Smaalen, S.; Dinnebier, R. E.; Katzke, H.; Depmeier, W. J. Solid State Chem. 1997, 143, 129. (7) Depmeier, W.; Buehrer, W. Acta Crystallogr., Sect. B 1991, 47, 197. (8) Depmeier, W. Acta Crystallogr., Sect. C 1984, 40, 226. (9) Depmeier, W. Acta Crystallogr., Sect. B 1988, 44, 201. (10) Depmeier, W.; Yamamoto, A. Mater. Sci. Forum 1991, 79, 763. (11) Kondo, R. J. Ceram. Assoc. Jpn. 1965, 73, 1. (12) Hu, X.; Depmeier, W.; Wildermuth, G.; Doyle, S. Z. Kristallogr. 1996, 211, 679. (13) Scheikowski, M.; Mu¨ller Buschbaum, H. Z. Naturforsch, B: Chem. Sci. 1996, 51, 883.
5954 Inorganic Chemistry, Vol. 43, No. 19, 2004
whose tetrahedral [AlO2]∞ host lattice forms large cavities where strontium cations and Bi2O3 clusters are located. The latter results suggest that the association of bismuth-oxygen clusters to large cations such as strontium may be a very fruitful direction of research for the discovery of new aluminates involving large cages or tunnels. We have revisited the system Sr-Bi-Al-O, using solid-state techniques and working in a sealed tube. We describe here the synthesis, crystal growth, and structure of a new bismuth aluminate, Sr33Bi24+δAl48O141+3δ/2, with δ ) 0.25, whose tetrahedral “Al-O” framework consists of huge spherical cages “Al84O210” derived from the D2d isomer of C84 fullerenes,15 forming a closed packed face centered cubic array. We also show that, inside the “Al84” spheres, the oxygen, strontium, and bismuth atoms form concentric spheres, leading to an onion-skin-like subnanostructure. Experimental Section Synthesis and Crystal Growth. The Sr33Bi24+δAl48O141+3δ/2 crystals were grown by classical solid-state techniques, grinding intimately a mixture of 0.5824 g of Bi2O3, 0.6578 g of SrO2, and 0.3313 g of Al2O3. The mixture was pressed into pellets, introduced in a gold tube, and sealed in an evacuated silica ampule. The sample was heated at 1200 °C for 48 h, slowly cooled to 1000 °C for 100 h, kept at this temperature for 48 h, slowly cooled to 600 °C for 100 h, kept at this temperature for 24 h, and slowly cooled to RT (14) Bakakin, V. V.; Podberezskaya, N. V.; Mazus, M. D.; Kozeeva, L. P.; Shaburova, V. P.; Malinovskii, T. I. Zh. Strukt. Khim. 1994, 35, 92. (15) Okada, S.; Saito, S. Chem. Phys. Lett. 1996, 252, 94.
10.1021/ic049679o CCC: $27.50
© 2004 American Chemical Society Published on Web 05/29/2004
New Aluminate with a Fullerenoid Structure Table 1. Crystallographic Data for Sr33Bi24+δAl48O141+3δ/2 chemical formula ) Sr33Bi24+δAl48O141+3δ/2 (δ ≈ 0.25) a ) 25.090(6) Å b ) 25.090(6) Å c ) 25.090(6) Å R ) 90° β ) 90° γ ) 90° V ) 15794(7) Å3 Z)4
Table 2. Atomic Parameters of Sr33Bi24+δAl48O141+3δ/2
fw ) 11517.6 g space group ) F4h3m (No. 216) T ) 20°C λ(Mo KR) ) 0.71073 Å Dcalc ) 4.84 g.cm-3 µ ) 38.34 mm-1 R(Fo) ) 0.0400a Rw(Fo2) ) 0.0818b
a R(F ) ) ∑||F | - |F ||/∑|F |. b R (F 2) ) {∑[w(F 2 - F 2)2]/ o o c o w o o c ∑[w(Fo2)2]}1/2.
(room temperature) for 82 h. Four resulting products were obtained, yellow-orange crystals of Sr33Bi24+δAl48O141+3δ/2 and white, green, and black tiny crystals of unidentified compounds. The quantitative synthesis in the form of polycrystalline powder was carried out also by solid-state reaction but from a stoichiometric mixture of oxides Bi2O3, SrO2, and Al2O3 and of Al in order to obtain the final composition Sr33Bi24+δAl48O141+3δ/2. The mixture was inserted in a gold tube placed in an evacuated silica ampule, heated at 850 °C for 48 h, and cooled to room temperature for 16 h. By this method, a monophasic polycrystalline material was obtained. The synthesis has been performed in a silica ampule in order to avoid the carbonatation of SrO2 and the oxidation of Al in air. In order to avoid contact with silica, a gold tube was used rather than an alumina tube, which can react with the sample. X-ray Single Crystal Study. A yellow platelet of Sr33Bi24+δAl48O141+3δ/2 with dimensions 0.111 × 0.060 × 0.050 mm3 was chosen for the crystal diffraction study. The data were collected on a Bruker-Nonius Kappa CCD four circles diffractometer equipped with a bidimensional CCD detector. Pertinent parameters for the data collection are reported Table 1. The cubic cell parameters were refined using the whole data set. The data were corrected for Lorentz and polarization effects. The extinction conditions, h + k ) 2n + 1, k + l ) 2n + 1, and h + l ) 2n + 1, are consistent with the following space groups: Fm3m (No. 225), F4h3m (No. 216), F432 (No. 209), Fm3 (No. 202), and F23 (No. 196). The heavy atom method was used for the structure determination. The calculations were performed using the SHELX 97 programs package.16 Whereas no solutions were found using the Fm3m space group, a structural model was obtained using the F4h3m one. The refinement, using the data set corrected from the absorption by Gaussian integration method, leads to the agreement factors R(Fo) ) 0.04 and Rw(Fo2) ) 0.0818 with the atomic parameters reported Table 2. In this model, several disorders exist. First, the Bi(3) site is partially occupied (at 69%); such occupation has been introduced because the electronic density observed on this site is low and because the Bi(3) environment is characteristic of a bismuth site (see Bi(3) environment in the description part). Second, several oxygen atoms have been split on sites located close to symmetry elements, because when they were placed on the symmetry elements they exhibit high thermal factors (being about four times higher than for the other oxygen atoms) and electronic residues are observed nearby on the difference Fourier maps. Thus, the O(3) and O(11) atoms have been split each on two sites located close to an m mirror: the O(8) atom has been split on 2 sites located in an m mirror but close to the intersection of two m mirrors, and the O(13) atom has been split on three sites close to a 3-fold axis. Third, the O(10) site is partially (16) Sheldrick, G. M. SHELX-97; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
atom
Wyckoff position
x
y
z
Ueqa/Uiso
Bi(1) Bi(2) Bi(3) Sr(1) Sr(2) Sr(3) Sr(4) Sr(5) Al(1) Al(2) Al(3) Al(4) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) O(12) O(13)
16e 48h 48h 4c 48h 48h 16e 16e 48h 48h 48h 48h 24f 48h 96i 96i 48h 24g 16e 48h 48h 48h 96i 96i 48h
0.85005(4) 0.29987(3) 0.94475(4) 0.75 0.82763(6) 0.17534(7) 0.92946(8) 0.5870(1) 0.0468(2) 0.0895(2) 0.7942(2) 0.4545(2) 0. 0.0259(6) 0.0421(7) 0.1577(4) 0.0772(4) 0.75 0.8269(6) 0.5100(7) 0.4047(4) 0.796(1) 0.900(1) 0.2730(7) 0.331(2)
0.85005(4) 0.29987(3) 0.94475(4) 0.25 0.82763(6) 0.17534(7) 0.92946(8) 0.5870(1) 0.0468(2) 0.0895(2) 0.7942(2) 0.4545(2) 0. 0.1083(4) 0.0585(7) 0.0775(4) 0.0772(4) 0.75 0.8269(6) 0.4900(7) 0.4853(6) 0.890(2) 0.826(1) 0.3597(6) 0.372(2)
0.85005(4) 0.59320(3) 0.74886(6) 0.75 0.46345(9) 0.99084(9) 0.92946(8) 0.5870(1) 0.1345(3) 0.2444(3) 0.1177(3) 0.3661(3) 0.1121(9) 0.1083(4) 0.2042(6) 0.2356(4) 0.3120(6) 0.1476(8) 0.1731(6) 0.345(1) 0.4047(4) 0.796(1) 0.9206(9) 0.5388(6) 0.628(2)
0.0156(4)a 0.0198(3)a 0.0238(5)a 0.007(1)a 0.0132(5)a 0.0218(6)a 0.0153(9)a 0.026(1)a 0.011(2) 0.009(1) 0.007(1) 0.011(1) 0.015(5) 0.015(3) 0.010(5) 0.015(2) 0.012(3) 0.011(5) 0.011(6) 0.014(7) 0.018(4) 0.07(2) 0.039(8) 0.055(4) 0.06(2)
a
Ueq )
1/
occ
0.688(2)
0.5
0.5 0.61(9) 0.5 0.333333
3∑Uij.
occupied, because if a full occupancy is introduced, the thermal factor is high and no electronic residues can be observed nearby on the difference Fourier map. Moreover, to ensure the charge balance in the chemical formula, partial occupancies have to be introduced on the oxygen sites. In order to propose a model with less disorder, we checked whether the crystal structure could be better described in a cubic and less symmetric space group. The model found with the F4h3m space group indicates that no 4-fold axes and no inversion centers exist in this structure; consequently, the F432 and the Fm3 space groups have been discarded. On the opposite, the suppression of the m mirrors and the replacement of the 4h axes by 2-fold axes allow us to describe the structure with F23. The refinement in this space group leads to a structural model very close to the F4h3m one with R(Fo) ) 0.0442 and Rw(Fo2) ) 0.0883, 1886 independent reflections with I > 3σ(I), and 126 parameters. In this model, the atoms corresponding to Bi(3) and O(10) sit on general positions, and they exhibit partial occupancies and thermal factors equal to those calculated for the previous model. The atoms corresponding to O(8) and O(13), located close to 2-fold and 3-fold axes, respectively, exhibit thermal factors equal to those calculated for the previous model. The atoms corresponding to O(3) and O(11) sit in general positions, and their isotropic thermal factors (equal to 0.039(5) and 0.09(2) Å2, respectively) are much higher than those in the F4h3m model. The F23 model does not improve the structural description (it even offers a worse model for O(3) and O(11)); consequently, we decide to keep the F4h3m description. Note that, to clarify the representation of the structure, the O(3), O(8), O(11), and O(13) atoms were not split on the drawings.
Description of the Structure and Discussion The crystal structure of this new aluminate consists of a 3D-framework of corner-sharing AlO4 tetrahedra, [Al48O94]∞ (Figure 1) containing strontium cations and bismuth-oxygen clusters. The [Al48O94]∞ framework can be described as the assemblage of “Al48O106” cubic units through the corners of their tetrahedra, displayed at the nodes of a face centered Inorganic Chemistry, Vol. 43, No. 19, 2004
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Figure 1. Representation of the [Al48O94]∞ aluminate framework of Sr33Bi24+δAl48O141+3δ/2 showing the face centered cubic arrangement of four Al48O106 cubic units within a unit cell. (For clarity, the cubic units located at 0 < x < 0.5 and 0.5 < x
