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M.M. Eddy University of California at Santa Barbara, Santa Barbara, California 93106

C.A. Fyfe.G.T. Kokotailo, and H. Strobl Guelph Waterloo Centerfor Graduate work in Chemistry, Guelph Campus, Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario NIG 2Wl, Canada

D.E. Cox Brookhaven National Laboratory, Upton, New York 11973

(Received 16 October 1987; accepted 11 January 1988) High-resolution nuclear magnetic resonance (NMR) spectra and synchrotron x-ray powder diffraction data have been obtained from a well-crystallized highly dealuminated sample of the zeolite ZSM-11. The Rietveld profile technique has been applied to the synchrotron data to give the first detailed refinement of the idealized structure derived ten years ago by distance leastsquares modeling methods [G. T. Kokotailo, P. Chu, S. L. Lawton, and W. M. Meier, Nature 275,119(1978)], which involves 54 variable atomic positional parameters. The structure is tetragonal (a = 20.065 A,c = 13.408 Aat 25 °C) and consistent with the previously reported tetragonal space group / 4w2, but the NMR spectra indicate local deviations from this symmetry that disappear at 100 °C.

I. INTRODUCTION A number of recent articles on zeolites have demonstrated the value of high-resolution nuclear magnetic resonance (NMR) or powder diffraction techniques to elucidate details of their structures. '~5 With the use of the Rietveld profile fitting method,6 several quite complex structures have been refined from powder data including a constrained refinement of that of the commercially important zeolite catalyst ZSM-5, in which there are 133 variable positional parameters.7 The new generation of very high-resolution neutron powder instruments at the Rutherford-Appleton Laboratory,8 and the Institute Laue-Langevin,9 and the triple-axis x-ray diffractometer at the Brookhaven National Synchrotron Light Source10 should extend the scope of powder diffraction techniques to considerably more complex problems, l ' including the use of ab initio methods for the solution of unknown structures, as recently demonstrated for FeAsO4 n and a-CrPO 4 . 13 In order to take full advantage of these new instruments, it is essential to prepare well-crystallized material in order to minimize unwanted broadening of the diffraction peaks from particle size effects, which implies a mean crystallite size of 0.5 //m or more. Although this is relatively straightforward for ZSM-5, it has not hitherto been possible to prepare such well-crystallized samples of the zeolite ZSM-11. This is the end member of the J. Mater. Res. 3 (3), May/Jun 1988

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pentasil family of high-silica zeolites,14"16 and has a body-centered tetragonal unit cell (approximate dimensions a = 20.1 A, c = 13.4 A, space groupI4m2), which is closely related to the orthorhombic cell of ZSM-5.17 Its framework topology was derived from modeling and distance least-squares (DLS) refinement,18 which gave a simulated x-ray powder diffraction pattern similar to the experimental pattern from the h