D031: The Topology Of Alpo4-53(C) Determined By The Focus Method

D031

The Topology of ALPO₄-53(c) Determined by the Focus Method. Ralf W. Grosse-Kunstleve^* and Richard M. Kirchner^#, ^*Dept. Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, ^#Chemistry and Biochemistry Dept., Manhattan College, Bronx, NY 10471

FOCUS, a new structure determining method, revealed the topology of AlPO-53(c) from powder diffraction data. The FOCUS method¹ incorporates chemical information used in model building into the structure determination process. FOCUS combines automatic Fourier recycling (using integrated intensities extracted from the powder data and random starting phases) with a specialized framework search specific to zeolite structures.

AlPO₄-53 was synthesized by S.T. Wilson at UOP. The as synthesized sample, designated AlPO-53(a), was calcined at 400deg.C for 45 hours to produce a new phase, AlPO-53(b). Heating AlPO-53(b) to 800deg.C yields a third phase, AlPO-53(c). Synchrotron xray powder diffraction data on AlPO-53(b) and AlPO-53(c) were collected by J.J. Pluth at NSLS X7A.

Although the synchrotron data contained significant contributions from impurities (primarily AlPO-53(b)), it took only a matter of hours from processing the raw synchrotron data to determining and confirming by DLS refinement (R_DLS = .004) the new topology of AlPO-53(c) in space group C2 (a = 16.4, b = 5.1, and c = 13.5 Å, [beta] = 88.3deg.). A Rietveld refinement is in progress.² The topology of AlPO-53(c) can be described as a brw net in the ac plane with the 6 and 8-ring pores parallel to b. The highly distorted 4, 6, and 8-rings in AlPO-53(b)³ transform to symmetric 4, 6, and 8-rings in AlPO-53(c).

¹Grosse-Kunstleve, R.W., McCusker, L.B. and Baerlocher, Ch., J. Appl. Cryst. (1997) submitted.

²Kirchner, R.M., Grosse-Kunstleve, R.W., Pluth, J.J, and Smith, J.V., in preparation.

³After determining the structure of AlPO-53(b) in 1992 we realized that it was the tetrahedral equivalent of AlPO-EN3 (Parise, J.B., in "Zeoltes" (Ed. B. Drzaj, S. Hocevar, and S. Pejovnik) Elsevier, Amstersam, 1984, 271.)