STRUCTURE DETERMINATION FROM SMALL CRYSTALS OF 2 ALUMINOPHOSPHATES, CRAPO-14 AND SAPO-43

Small single crystals, ca 10(5) mum3, of two aluminophosphates have be en used to determine their structures. Both compounds were synthesized with the aim of incorporating chromium into the framework, and for Cr APO-14 the X-ray diffraction results show that this has been achieved. For CrAPO-14, Al3.96Cr0.04(PO4)4(OH).C3H10N.H2O, data recorded on a R igaku AFC-5R diffractometer (Cu Kalpha) and, independently, on an Enra f-Nonius FAST diffractometer (Mo Kalpha), showed the structure to be l ike that of GaPO-14 [Parise (1986). Acta Cryst. C42, 670-673]; alumini um atoms occupy four-, five- and six-coordinated sites, and 4-5% of th e aluminium in the six-coordinate site is replaced by chromium. For SA PO-43, Al2(PO4)2(C3H10N), data were recorded independently on the AFC- 5R (Cu Kalpha) and on a FAST diffractometer with synchrotron radiation of wavelength 0.895 angstrom; the structure is like that of gismondin e [Alberti & Vezzalini (1979). Acta Cryst. B35, 2866-2869], but replac ement of Al by Cr to a significant extent could not be established. Fr amework Al, P and O atoms are located with e.s.d.'s of 0.001-0.005 ang strom, template atoms with e.s.d.'s of ca 0.01 angstrom in CrAPO-14, a nd larger e.s.d.'s in SAPO-43 where there is disorder in the template- molecule position. In all these respects the two independent determina tions for each structure are in agreement. The effectiveness of the di fferent methods of intensity-data collection is compared.