J . Phys. Chem. 1990, 94, 3365-3367
is proportional to the fractal dimension of the percolation cluster, has been found to increase both with conductivity and with temperature. The rate constant for transfer and reaction has the previously found value ((1-2) X IO9 M-l s-]; see ref 4) for the percolation threshold.
3365
Acknowledgment. We acknowledge financial aid from the Greek General Secretariat of Research and Technology. Registry No. SDS, 151-21-3; Ru(bpy)32*, 151 58-62-0; Fe(CN):-, 13408-62-3;dcdecane, 112-40-3; heptane, 142-82-5;pentyl alcohol, 714 1-0.
AIPO,-25: Framework Topology, Topotactic Transformation from AIP0,-21, and High-Low Displacive Transition James W. Richardson, Jr.,*,t,bl Joseph V. Smith,$,$and Joseph J. Plutht3SJ Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, Illinois 60439, and Center for Advanced Radiation Sources, Department of Geophysical Sciences, and Materials Research Laboratory, The University of Chicago, Chicago, Illinois 60637 (Received: November 6 , 1989: In Final Form: March 12, 1990)
Upon calcination, as-synthesized AIP04-21 transforms to A1P04-25, perhaps topotactically. Room-temperature A1P04-25 has unit cell parameters a = 15.085 (2) A, b = 18.761 (2) A, c = 8.363 (1) A; Ibam (72). The four-connected tetrahedral net of AIP04-25 appears to retain the (468)2(682)1three-connected 2D net of A1P04-21, but the double-crankshaft chains disappear. Instead, up and down connections alternate to yield dbs chains. A1P04-25 inverts to the geometrically regular high variety near 530 K, with the accompanying halving of one axis. Time-of-flight neutron powder diffraction data at 593 K yielded a good Rietveld refinement for the high-temperaturestructure with artificially disordered Alo,jPo,jin an orthorhombic cell with a = 9.4489 (4) A, b = 15.2028 (5) A, c = 8.4084 (3) A, Acmm (67).
A1P04-21, a member of a new class of materials,I is an assynthesized phase2 whose AI and P atoms3*,lie at the vertices of a four-connected 3D net. All the P atoms and one-third of the AI atoms lie in near-regular oxygen tetrahedra, but two-thirds of the AI atoms are bridged in pairs by a nonframework hydroxyl that causes distortion of the tetrahedron of framework oxygens. Upon heating, the AIPO,-21 transforms to AIP04-25 with loss of H 2 0 and encapsulated organic species. The structure of AIP04-25 was unknown, but the suggestion was made3-4that its framework topology was that of AIP04-21 and that its geometry would be more regular because of the removal of the bridging hydroxyl. Although the observed powder diffraction pattern of AIP04-25 was similar to a calculated pattern for the regular tetrahedral equivalent of AIP04-21, there were numerous intensity discrepancies and unexplained weak lines. We now show that AIP04-25 has a new topology and that there is a high-low displacive transition near 530 K analogous to that in tridymitej and other framework structures. The A1P04-25 structure contains the same type of three-connected 2D net as A1P04-21, but it has an up-down-up-down chain instead of the up-up-down-down chain of A1P04-21. This partial structural relationship allows the possibility of a topotactic transformation similar to that for the transition of zeolite (Na,TMA)-E(AB) to a sodalite-type material6 above 633 K, and of AIPO,-C to AIP04-D.’ Experimental Section
AIP04-25 was prepared by calcining A1P04-21 in air at 773 K for 40 h. A powder neutron diffraction pattern at 298 K (Figure 1) was indexed on an orthorhombic cell with a = 15.085 (2) A, b = 18.761 (2) A, c = 8.363 ( I ) 8,. All hkldiffractions with k odd were weak and obeyed k odd, I even. Determination of the space group for a structure with a weak class of diffractions is notoriously uncertain, but model structures with various space groups compatible with the observed diffractions were investigated without obvious success. Progressive heating of a new sample of AIP04-21 in a Guinier-LennE X-ray camera generated A1P04-25
* Author to whom correspondence should be addressed.
’Argonne National Laboratory.
$Center for Advanced Radiation Sources. Department of Geophysical Sciences. Materials Research Laboratory.
0022-3654/90/2094-3365$02.50/0
TABLE I: Atomic Coordinates and Equivalent Thermal Displacements of AIP0,-25 at 593 K“ atom site sym X Y Z 0.3535 (13) 0.0982 (6) 0.1987 (12) T(1) 160 1 0.1566 (15) 0.2500 0.3142 (12) T(2) 8m m 0.2500 2 0.3017 (8) 0.0000 O(1) 81 0.5000 0.1275 (5) 0.2500 O(2) 8k 2 0.2317 (8) 0.1625 (5) 0.2497 (13) O(3) 160 1 O(4) 8m m 0.3308 (IO) 0.0971 (6) 0.0000 O(5) 4e 2 / m 0.0000 0.2500 0.2500 0.5000 O(6) 4g m m 0.1076 (24) 0.2500
uq,A2 0.100
0.035 0.074 0.079 0.096 0.112 0.070 0.219
“T = Alo,5P,,5;a = 9.4489 (4) A, b = 15.2028 (5) A, c = 8.4084 (3)
A; A c m m (67).
which lacked the k odd diffractions above -530 K. Cooling and subsequent heating demonstrated the occurrence of a displacive high-low transition. Time-of-flight neutron diffraction data at 593 K showed that the (750), (570), and (710) diffractions of the low structure retained very weak intensity just above background level (Figure I ) . Ignoring this trivial deviation from an idealized high-temperature structure with halved b, the data at 593 K were indexed on an orthorhombic cell with the cell dimensions and space group in the abstract (note relabeling of a and b to make b > a ) . The new dimensions and space group are incompatible with the four-connected net in AIP04-21 and require that the connectivity be changed. However, the c repeat remains at 8.5 A, and the ab section of 9.5 X 15 8, is compatible with the (468)2(682)1 three-connected 2D net (denoted brw in ref 8 ; Figure 2a) in the AIP04-21 3D net (denoted ATF in ref 9, but now changed to A T 0 (1) Wilson, S. T.; Lok, B. M.; Messina, C. A,; Cannan, T. R.; Flanigen, E. M. J . A m . Chem. Soc. 1982, 104, 1146-1 167. (2) Wilson, S. T.; Lok, B. M.; Flanigen, E.M. US Patent N o 4310440. (3) Bennett, J. M.; Cohen, J. M.; Artioli, G.; Pluth, J . J.; Smith, J. V. Inorg. Chem. 1985, 24, 188-193. (4) Parise, J. B.; Day, C. S. Acta Crystallogr. 1985, C41, 515-520. (5) Florke, 0. W. Forschr. Mineral. 1967, 44, 181-230. (6) Meier, W. M.; Groner, M. J . Solid Store Chem. 1981, 37, 204-218. (7) Keller, E. B. Doctoral Thesis, ETH, Zurich, 1987. (8) Smith, J. V. Zeolites: Facts, Figures, Future, Jacobs, P. A,, van Saten, R. A., Eds.; Elsevier: New York, 1989; pp 29-47. (9) Meier, W. M.; Olson, D. H. Atlas of Zeolite Structure Types, 2nd revised ed.; Butterworths: London, 1987.
0 1990 American Chemical Society
3366 The Journal of Physical Chemistry, Vol. 94, No. 9, 1990 TABLE 11: Interatomic Distances (A, and Andes atoms distance T( 1k O ( 1 1.630 (8) 1.517 (1 1 ) 1.570 ( 1 2) 1.684 ( I O ) 1.600 ~~~
Letters
(ded
~
atoms O(l)-T(l)-O(2) o(I )-T( I )-0(3 j O( l)-T(l)-O(4) O(2)-T( 1)-0(3) 0(2)-T( 1)-O(4) O(3)-T( 1)-0(4) 0(3)-T(2)-0(3) 2 0 ( 3)-T( 2)-O( 5) 2 0 ( 3)-T( 2)-0(6) O( 5)-T(2)-0(6)
1.602 (9) 1.575 (14) 1.630 (8) 1.602
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3
10000
atoms T ( 1 )-O( 1)-T( 1) T( l)-O(2)-T(l) T( 1)-0(3)-T(2) T( 1)-0(4)-T( 1 ) T(2)-O( 5)-T( 2) T(2)-0(6)-T( 2)
angle 117.9 (8) 106.1 (8) 102.4 (6) 114.1 (7) 114.7 (8) 100.6 (6) 112.2 (9) 107.4 (5) 116.8 (5) 93.5 (10)
angle 145.0 (10) 145.8 ( I O ) 159.1 (8) 165.3 ( I O ) 180.0 147.0 (19)
298K
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.
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.
.
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.
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.
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Figure 1. Neutron powder diffraction data for the high and low structures of AIP04-25 at 593 and 298 K, respectively. Five reflections with k odd are marked.
b a
by the International Zeolite Association Structure Commission). Hence, it appeared that the correct net of A1P04-25 (to be denoted ATV) would turn out to be another type of union of the crankshaft chain (denoted c8,Io)with the brw net. Indeed an unpublished theoretical net (Figure 2) yielded a powder diffraction pattern that provided a good fit with the neutron diffraction pattern obtained for high-A1P04-25 (Figure 3). This theoretical net is now listed as no. 65 1 in the Catalog of Frameworks maintained by the Consortium for Theoretical Frameworks8 A systematic enumeration of all 3D frameworks obtained from the union of c and brw will be presented elsewhere, together with theoretical powder diffraction patterns. Figure 2 shows detailed ab projections of the A T 0 and ATV four-connected 3D nets. Each vertex of the brw three-connected 2D net is labeled with an open or a closed symbol to show whether the fourth edge projects upwards or downwards to adjacent parallel brw nets. In the ATV net, there is complete alternation of the upwards and downwards edges (stereoplot, Figure 4). Trial atomic coordinates for an assumed disordered (A1,P) atomic distribution were obtained by a distance-least-squares calculation." Neutron data from the f90° detector banks of the IPNS General Purpose Powder Diffractometer were analyzed with the Rietveld refinement technique,12 modified for use with ~?~~ time-of-flight data from a pulsed neutron s o u r ~ e . ~Conventional background scattering was fitted with a six-parameter analytical function.I5 The coherent neutron scattering lengths (fm) are Alo,sPo,s,4.29; 0, 5.80. The range of reciprocal space was d = 1.038-4.038 A. Fourier-filtering of the backgroundJ6and an(IO) Smith, J. V. Chem. Rev. 1988,88, 149-182. ( I I ) Baerlocher, Ch.; Hepp, A.; Meier, W . M. DLS-76; A Program f o r the Simulation of Crystal Structures by Geometric Rejnement; Institute for Crystallography, ETH, Zurich, 1976. ( I 2) Rietveld, H. M. J . Appl. Crystallogr. 1969, 2, 65-71. (13) Von Dreele, R. B.: Jorgensen, J. D.; Windor, C. G. J. Appl. Crystallogr. 1982, I S , 581-589. (14) Jorgensen, J. D.; Rotella, F. J. J. Appl. Crystallogr. 1982, I S , 27-34. ( I 5) Rotella, F. J. Users Manual for Rietveld Analysis of Time-of-Flight Neutron Powder Diffraction Data at IPNS, Argonne National Laboratory, IL, 1986. (16) Richardson. Jr.. J. W.: Faber, Jr., J. Ado. X-ray Anal. 1986, 29, 143-152.
AT0
AIP04-21
ATV
AIPO4-25
b
Figure 2. Projections of the connectivities of the A T 0 (AlI-d4-2l) and ATV (AIP04-25) 3D nets. The lines connect the vertices of the brw 2D net, and the open and closed symbols distinguish between vertices that are connected either upwards or downwards. Circular and square symbols distinguish between alternate vertices occupied by ordered AI and
P.
isotropic refinement yielded R p = 13.3%, R,, = 4.1%. Tables I and I1 give the atomic coordinates, equivalent isotropic thermal parameters, and interatomic distances, and angles for AIP04-2 5 .
The Journal of Physical Chemistry, Vol. 94, No. 9, 1990 3367
Letters 10000
dE
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i
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I
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Figure 3. Comparison of observed neutron powder data (crosses) of
AIP04-25 at 593 K with profile (curve) calculated from the model coordinates in Table I . The positions of Bragg reflections are shown by vertical line segments, and the discrepancy (on the same scale) by the lower profile.
Figure 4. Stereoplot of the ATV net.
Discussion The ATV net of AIP04-25 is topologically simpler than the A T 0 net of A1P04-21. All edges of the brw net are converted into crankshaft (c) chains instead of only one-third of the edges of the bnv net of ATO. The ATV cell has half the volume of the A T 0 cell, and there are two types of vertices with circuit symbol (66)I ( 465)2 instead of three types (43)I (42638)I (426282)I . Furthermore, the topologically simple up-down sequence around the brw net of ATV also occurs in the hex net of tridymite, the gml net of the AFI net of A1P04-5, the ael net of the AEL net of AIP04-I I , and the eoo net of VPI-5/AIP04-54 (nomenclature in ref 8; stereoplots in ref 9 and 17). Hence, the up-down alternation apparently leads to several materials that crystallize readily. (17) Richardson, Jr., J. W.; Smith, J. V.; Pluth, J. J. J . Phys. Chem. 1989, 93. 8212.
~
The ATV 3d net can be decomposed into various subunits listed in the Catalog of Frameworks:8 rings, 4,6, 8; I D units, afv, bhs, c, ecc; 2D units, brw, hex, polyhedral building units, afi, bog, lov, oop. Still to be resolved are some details of the A1P04-25 structure. The degree of AI,P ordering could not be resolved from the neutron powder data. Regular alternation of AI and P leads to the same cell dimensions, but space group Abm2 (no. 39). Loss of the mirror plane perpend!cular to c is "hidden" by the automatic overlap of hkl and hkl diffractions in a power pattern. A magic-angle-spinning nuclear magnetic resonance study should provide a direct test of the degree of AI,P ordering. The second detail involves the significant broadening of the X-ray and neutron diffraction for the present specimen of AIP04-25. Coupled with the observationI8 that a "single" crystal of GaP04-25 had a "high mosaic spread", it seems possible that crystals of AIP04-25 and presumably isostructural GaP04-25 consist of an aggregate of small domains. Electron imaging should provide information on the domain texture and on whether there are structural discontinuities or antiphase continuous changes at the domain boundaries. Scattering from the domain boundaries could explain the weak subsidary diffractions in the neutron data at 593 K. Furthermore, the presence of domain boundaries should smear out the low-high transition. Finally, the AlP04-21 to AIP04-25 transition has considerable resemblance to the AIPO,-C to AIP0,-D transition.' Both precursors contain double-crankshaft (cc) chains that are replaced by up-down-up-down (bhs) chains as the three-connected 2D net is retained (4.8.8 (fee) in C,D, and brw in 21,25). However, AIP04-C is a reversible dehydration product of A1PO4-H3,I9which has extra-framework H 2 0 bonded to octahedral AI,*O whereas hydroxyl-containing A1P04-21 transforms diretly to A1P04-25, at least under the heating conditions of the Guinier-Lenni camera. Major structural changes must occur for both the C,D and 21,25 transitions, and there is no analogy with the minor atomic movement proposed for the EAB to SOD transition.6
Acknowledgment. We thank S. T. Wilson and E. M. Flanigen for supply of the A1P04-21 specimen, and for discussion of the present results. Financial support was provided by NSF grant CHE 86-05 167 and a UOP grant-in-aid. J.J.P. is partly supported by the Materials Research Laboratory funded by N S F grant DMR 8519460. J.W.R. acknowledges J. Faber, Jr. and R. L. Hitterman for the use of their instrument at IPNS and the U S . Department of Energy for financial support under contract W-31-109-ENG-38. (18) P;rise, J. B. Acfa Crysfallogr. 1986, C42, 144-147. (19) d Yvoire, F. Bull. SOC.Chim. Fr. 1961, 1762-1776. (20) Pluth, J. J.; Smith, J. V . Acta Crysfallogr. 1986, C42, 1118-1120.
