Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.chem.msu.ru/rus/fullerenes/herview-paper-eng.pdf Äàòà èçìåíåíèÿ: Wed Jul 28 21:19:30 2004 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 04:01:25 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: dark energy

nmat1089PRINT

3/11/04

11:00 AM

Page 269

ARTICLES

The route to fullerenoid oxides
MARYVONNE HERVIEU*, BENJAMIN MELLõNE, RICHARD RETOUX, SOPHIE BOUDIN AND BERNARD RAVEAU
Laboratoire CRISMAT, UMR 6508 CNRS ENSICAEN, 6 bd MarÈchal Juin, 14050 CAEN Cedex 4, France *e-mail: maryvonne.hervieu@ismra.fr

Published online: 7 March 2004; doi:10.1038/nmat1089

Tetrahedral oxides, like silicates and aluminates, have attracted great interest due to their potential for numerous applications in various fields ranging from catalysis, ion exchange and molecular sieves, to thermoand

photoluminescence. In spite of their tetrahedral character, no effort has been made to date for establishing structural relationships between these tetrahedral oxides with different forms of carbon, for example, fullerenes. Here, we report for the first time an oxide that exhibits a three-dimensional framework of AlO4 tetrahedra forming huge `Al84' spheres, similar to those of the D2d isomer of the C84 fullerenes. These Al84 spheres, displayed in a face-centred-cubic lattice, are easily identified by high-resolution electron microscopy. We also show that this Sr33Bi24+Al48O141+3/2 aluminate exhibits an onion-skin-like subnanostructure of its Bi/Sr/O species located inside the Al84 spheres. The role of the original pseudo-spheric anion [Bi16O52­n
n

]--with n

vacancies ( )--in the stabilization of such a structure is discussed. This structure seems to be promising for the generation of a large family of fullerene-type (fullerenoid) oxides with various properties.
nature materials | VOL 3 | APRIL 2004 | www.nature.com/naturematerials

etrahedral oxides involving species such as Si and Al have received considerable attention due to their great potential for various applications. Several strontium aluminates have indeed been recently studied as pigments for photoluminescence or thermoluminescence1,whereas silicates and silicoaluminates of the zeolite and ultramarine family are currently investigated for their adsorptive and ion-exchange properties, their behaviour as molecular sieves and their catalytic properties2­8. These oxides exhibit various complex structures, which can be better understood by considering their topology9,10, so that each tetrahedron is currently represented by its metallic (M) atom (Al or Si), allowing the large cavities and tunnels to be easily identified in the three-dimensional (3D) frameworks, by connecting Al or Si atoms by straight lines (see refs 11,12 for a review). Bearing in mind this mode of representation, it is of interest to compare the M = Si, Al frameworks of zeolites with those of fullerenes. This is illustrated, for instance, for the sodalite cage of ultramarine Na8­10Al6Si6O24S2­4 (Fig. 1a) built up of hexagonal (Al, Si)6 and square (Al, Si)4 `windows'. This sodalite cage can be compared to the C60 fullerene13 (Fig. 1b), which consists of C60 spheric molecules built up of edge-sharing C5 pentagons and C6 hexagons. This topologic analysis suggests that it should be possible to synthesize fullerenoid oxides in which metallic atoms would form, similarly to fullerenes--bucky balls--whose cohesion should be ensured by oxygen atoms located half the distance between two metallic atoms, so that each metallic atom would exhibit a tetrahedral coordination. In this paper, we report the first fullerenoid oxide, which consists of Al84 spheres similar to one of the fullerene C84 isomers14, and we show that the Al84 spheres form a face-centred-cubic array 3D framework. Our strategy for the synthesis of fullerenoid oxides is based on the fact that the realization of such Mn spheres in the form of a 3D framework of tetrahedra requires the Mn spheres to be stuffed with voluminous species to ensure the stability of the structure. Each MnO(3n+2)/2 sphere could be stabilized by various organic templates (ions or molecules), using hydrothermal synthesis, but it is a risk to introduce hydroxyl groups in the framework, as this is likely to decrease the stability of the materials. The second possibility is to introduce large
269

T

©2004 Nature Publishing Group


nmat1089PRINT

3/11/04

11:00 AM

Page 270

ARTICLES
a a b

c b

Figure 2 Al84 and C84 fullerene. a,b, The Al84 spheres (a) are similar to the D2d isomer of the C84 fullerene, and exhibit pentagon pairs (b). c, The tetragonal coordination of the Al generates Al84O120 spheres.

Figure 1 Ultramarines and C60 fullerene. a,b, The geometry of the sodalite cage of ultramarines (a) can be considered as a quasi dual form of the spheric molecules of C60 fullerene (b).

cations to neutralize the negative charges formed by the MnO(3n+2)/2 spheres. We have prioritized this second direction of research, as it should allow the procedure to be done under normal pressure. Consideration of the previous studies carried out on 3D aluminates shows that among the numerous compounds that have been isolated, the aluminate Sr6Bi2O3 (AlO2)12 (ref. 15) is of great interest, as its tetrahedral framework [AlO2] forms large cavities and tunnels where Sr2+ cations and Bi2O3 groups are located. Starting from this observation, we have revisited the system SrO­Bi2O3­Al2O3.During this investigation we have isolated the aluminate Sr33Bi24+Al48O141+3/2 by solid-state reaction, starting from a mixture of SrO, Bi2O3 and Al2O3. Single crystals of this new aluminate were also grown and studied by X-ray diffraction. The detailed method for synthesis, crystal growth and structure determination will be reported elsewhere.
270

This aluminate exhibits a large cubic cell, a = 25.09 å, and belongs to ­ the space group F 43m,containing four formulae per unit cell. Its crystal structure appears, at first sight, rather complex: it has a 3D framework of corner-sharing AlO4 tetrahedra, forming large spherical cages containing Sr2+ cations and bismuth­oxygen clusters. Moreover, additional Sr2+ cations sit between the cages. The first important feature of this structure deals with the aluminium lattice. The aluminium atoms form huge spheres Al84 (Fig. 2a), built up of Al5 pentagons and Al6 hexagons, similarly to the fullerenes. In fact, this configuration characterized by pentagon pairs (Fig. 2b) corresponds to the D2d isomer, the one most currently encountered for the C84 fullerene14. Nevertheless, the size of the Al84 sphere is much larger than that of the C84 fullerene, showing a diameter of 18.5 å, compared with 8.5 å for C84.This great size difference is due to the oxygen atoms, located approximately half way between two adjacent aluminium atoms, so that the Al84 sphere generates an Al84O210 sphere of corner-sharing AlO4 tetrahedra (Fig. 2c). The second remarkable characteristic concerns the arrangement of the Al84 spheres, which form a face-centred-cubic array as shown from the projection of the aluminium lattice along the [100] direction (Fig. 3). Moreover, each Al84 sphere shares a hexagonal Al6 face with twelve other identical spheres forming the [Al] 3D framework. In this
nature materials | VOL 3 | APRIL 2004 | www.nature.com/naturematerials

©2004 Nature Publishing Group


nmat1089PRINT

3/11/04

11:00 AM

Page 271

ARTICLES

O7.4 A184 O Bi16
126

4.6

O Sr32Bi8.25
3.75

40

Figure 3 Projection of the Al framework of the bismuth aluminate Sr33Bi24+Al48O141+3/2 along [100], showing a face-centred-cubic array of spheres sharing Al6 hexagons.

Figure 4 The onion-skin-like subnanostructure of the BiSrO array contained in the Al84 spheres of Sr33Bi24+Al48O141+3/2. The colours refer to those adopted in Fig. 5.

respect, the aluminium network in this aluminate is very different from the fullerenes, in which the Cn spheres are isolated. Regarding the oxygen network, it is worth pointing out that one oxygen atom per aluminium atom is located outside of the Al84 sphere. This means that 84 oxygen atoms per Al84O210 sphere are located outside of the sphere. Twelve of these oxygen atoms form Al­O­Al bridges between two spheres, leading to the 3D framework of AlO4 tetrahedra. The other 72 oxygen atoms participate in the next Al84 spheres. The remaining 126 oxygen atoms (3/2 oxygen atoms per aluminium) plaster the wall inside the Al84 sphere, forming an O126 sphere. The third exceptional structural property resides in the onion-skinlike subnanostructure of the `BiSrO' array located inside the Al84 sphere as schematized in Fig. 4. The O126 sphere (Fig. 5a) is built up of corner-sharing triangular groups O3 forming hexagonal O6 and pentagonal O5 windows similar to the Al84 spheres, but sharing corners instead of edges. Inside the O126 sphere, the strontium and a part of the bismuth sites form a third concentric sphere Sr32(Bi8.25 3.75) (Fig. 5b), which consists of two interpenetrated spheres, the Sr32 sphere (blue coloured) built up of edge-sharing four-sided Sr4 and six-sided Sr6 rings, and the partially occupied Bi8.25 3.75 sphere (yellow coloured), built up of Bi4 squares and Bi3 triangles. The fourth O40 sphere (Fig. 5c) consists of O3 triangles and O4 squares. The fifth sphere is represented by the central group Bi16 (Fig. 5d), forming edge-sharing Bi3 triangles with Bi­Bi distances ranging from 3.54 å to 4.21 å. Finally, inside the latter sphere there exists a truncated O12 tetrahedron (Fig. 5e), which is only 61.5% occupied. These fascinating structural specificities are clearly illustrated by the high-resolution electron microscopy (HREM) images. Two examples are given in Fig. 6. In the first image (Fig. 6a), recorded for a focus value close to Scherzer (close to ­300 å for the microscope), the highelectron-density zones appear as darker spots. The contrast of this
nature materials | VOL 3 | APRIL 2004 | www.nature.com/naturematerials

image can be described through a regular arrangement of dark butterfly wings, surrounded by darker crowns and separated by white crosses along [110] and single white dots elongated along [100] and [010]. The origin of the contrast is explained in Fig. 6b through the [001] projection of a single unit cell and an enlarged image. Two of the darker crowns surrounding the butterfly wings are represented by circles; and are drawn and superimposed on the image. The dark crown is associated to the complex projection of the atoms at the ball periphery and the butterfly wings to the positions of Bi and Sr atoms at the top of the spheres (see the projected structure). The white crosses of this Scherzer image are associated to the low electron density observed in between two tangent spheres in a compact plane and the elongated spots between two spheres located at different levels along c.The contrast generated by the Sr32(Bi8.25 4.75) spheres (observed for a focus value close to 50 å) is most spectacular (Fig. 6c). It consists of an array of alternating white crosses and small white circles along [100] and [010]. Only the Sr32(Bi8.25 4.75) spheres are projected along [001] on the drawing in Fig. 6d. The white crosses are associated with the Sr and Bi atoms located at the top of the spheres and at the tangency area between two adjacent spheres located at the same level, whereas the small white circles are associated to projection of the Bi/Sr atoms located between spheres at different levels. Attention must be drawn to the Bi16O52­n n anion, whose geometry is exceptional and is observed for the first time. This `pseudo-spherical' anion (Fig. 7a) consists of six bipyramidal units Bi2O8 and four BiO6 octahedra sharing their apices. In such an anion, the bipyramidal units are built up of two edge-sharing BiO5 pyramids (Fig. 7b) whose apical apex is shared by three Bi2O8 units. The 12 oxygen atoms of the common edges are 61% occupied and form the truncated O12 tetrahedron. They also form three corners of each BiO6 octahedron. The remaining oxygen atoms of the BiO5 and BiO6 polyhedra form the O40 sphere of the onion-skin-like structure. There is no doubt that the stereo-activity of
271

©2004 Nature Publishing Group


nmat1089PRINT

3/11/04

11:00 AM

Page 272

ARTICLES
a b

c

d

e

Figure 5 Geometry of the different spheres. a,O126; b,Sr32(Bi8.25

3.75

); c,O40; d,Bi16; and e,O12.

the 6s2 lone pair of Bi3+ governs the geometry of this pseudo-spherical anion, explaining also the existence of anionic vacancies, leaving room for the extension of its electronic lone pair. It is most probable that this anion, due to its great size and shape, is at the origin of the fullerene-like structure of this aluminate. In conclusion, a fullerenoid oxide, built up of Al84 huge spheres has been synthesized for the first time. The great similarity of this structure to that of the D2d isomer of C84 fullerenes opens the route to the exploration of other possible members in this series, varying the size of the Aln spheres, and their mode of connection by changing the nature and the amount of alkaline-earth cations with respect to the tetrahedral aluminium species, but also by considering the possibility of introducing other tetrahedral species on the aluminium sites, such as Si, Ge, Ga, Fe and so on, and other cations or anions inside the Aln sphere. As a consequence, these materials should rather be regarded as potential
272

for various properties and applications ranging from photoluminescence or thermoluminescence to magnetism, frequency doubling or nonlinear optical properties, and even to catalysis.
METHODS
The X-ray structure determination of this aluminate was carried out on a crystal of 0.111 â 0.60 â 0.05 mm3. The data were collected with a Brucker­Nonius Kappa CCD four-circle diffractometer equipped with a CCD detector and using the MoK radiation. The reciprocal space was registered up to = 30°, leading to a total of 8,153 reflections and 1,305 independent reflections with I > 3 (I ). With 90 refined parameters, the agreement factors are R(Fo) = 0.0400 and Rw(Fo2) = 0.0818. Fo and Fc are the observed and calculted structure factors and R(Fo) = ( ||Fo| ­ |Fc||)/( |Fo|), whereas Rw ={ [w (Fo2 ­ Fc2)2]/ [w(Fo2)2]}1/2,where w = 1/[2(Fo2) + (0.0401P)2]; (Fo2) is the error on Fo2, and P = (max(Fo2,0) + 2Fc2)/3. The electron-diffraction study was carried out with a JEOL 2010 electron microscope and the high-resolution electron microscopy with a TOPCON 002B (200 kV-Cs = 0.4 mm). Both microscopes

nature materials | VOL 3 | APRIL 2004 | www.nature.com/naturematerials

©2004 Nature Publishing Group


nmat1089PRINT

3/11/04

11:00 AM

Page 273

ARTICLES
a a

25 å

a b
b

b

b

b

a

a

c

25 å

Figure 7 Pseudo-spheric anion located in the heart of the spheres. a,b, Geometry of the Bi16O48­n n anion (a) forming Bi2O8 units of two edge-sharing BiO5 pyramids (b) associated to BiO6 octahedra.

were equipped with energy-dispersive spectrometers. The image calculations were carried out with MacTempas software.

a b
d

Received 12 January 2004; accepted 2 February 2004; published 7 March 2004. References
1. Ohta, M., Maruyama, M., Hayakawa, T. & Nishijo, T. Role of dopant on long-lasting phospor of strontium aluminate. J. Ceram. Soc. Jpn 108, 284­289 (2000). 2. Mandelcorn, L. (ed.) Non-Stoichiometric Compounds (Academic, New York, 1964). 3. Helfferich, F. Ion Exchange Properties (McGraw-Hill, NewYork, 1962). 4. Wilson, S. T., Lok, B. M., Masina, C. A., Cannan, T. R. & Flanigen, E. H. Aluminophosphate molecular sieves: a new class of microporous crystalline inorganic solids. J. Amer. Chem. Soc. 104, 1146­1147 (1982). 5. Guth, J. L., Kessler, H. & Wey, R. Stud. Surf. Sci. Catal. 28, 121 (1986). 6. Cheetham, A. K., Ferey, G. & Loiseau, T. Open-framework in inorganic materials. Angew. Chem. Intl Edn 38, 3268­3282 (1999). 7. Rabo, J. A. & Schoonover, M. W. Early discoveries in zeolite chemistry and catalysis at Union Carbide and follow up in industrial catalysis. Appl. Catal. A 222, 261­275 (2001). 8. Zones, S. I. & Davis, M. E. Zeolite materials: recent discoveries and future prospects. Curr.Opin. Solid State Mater. Sci. 1, 107­117 (1996). 9. OKeefe, M., Eddaoudi, L. H., Reineke, T. & Yaghi, O. M. Frameworks for extended solids: geometrical design principles. J. Solid State Chem. 152, 3­20 (2000). 10. FÈrey, G. Building units design and scale chemistry. J. Solid State Chem. 152, 37­48 (2000). 11. Wells, A. F. Structural Inorganic Chemistry 5th edn (Oxford Univ. Press, Oxford, 1993). 12. Smith, J. V. Topochemistry of zeolites and related materials 1. Topology and geometry. Chem. Rev. 88, 149­182 (1988). 13. KrÄtschner, W., Lamb, L. D., Fostiropoulos, K. & Huffman, D. R. Solid C60:a new form of carbon. Nature 347, 354­358 (1990). 14. Okada, S. & Saito, S. Number of extractable fullerene isomers and speciality of C84. Chem. Phys. Lett. 252, 94­100 (1996). 15. Bakakin, V. V. et al. The structure of frame strontium aluminate Sr6(Al12O24)Bi2O3 with inclusion of Bi2O3 molecule. Zh. Strukt. Khim. 35, 92­99 (1994). Correspondence and requests for materials should be addressed to M.H.

b

b

a

a

Figure 6 HREM evidence of the structural specificities of the fullerenoid aluminate. a,b, HREM images of the basal plane (a) and projection of the single unit cell (blue coloured) in relation to the enlarged image (b) for a focus value close to where the high-electrondensity zones appear as dark spots. c,d, HREM image (c) and projection of the Sr32(Bi8.25 4.75) spheres in relation to the enlarged image (d). The white squares represent the unit cell, whereas the circles and elongated white sticks outline the characteristic structural units at the origin of the contrast.

Competing financial interests
The authors declare that they have no competing financial interests.

nature materials | VOL 3 | APRIL 2004 | www.nature.com/naturematerials

273
©2004 Nature Publishing Group