CRYSTAL STRUCTURE OF AMMONIUM HEXAFLUOROCERATE(4) (NH4)2CEF6

The crystal structure of ammonium hexafluorocerate(IV), (NH4)2CeF6, has been determined from counter measurements of 561 reflections and refined by full-matrix least squares to an R factor of 0.032. The space group is Pbcn (no. 60); Dx = 3.05 and Dm = 3.05 ± 0.02 g/cm3. The unit cell has dimensions a = 7.026 (3), b = 12.098 (6), and c = 7.439 (8) Å; Z = 4. Of the 561 reflections measured, 389 were judged to be observed. The structure consists of infinite chains of eightfold coordinated cerium atoms parallel to the c axis, joined by NH4+ ions. The fluorine configuration about the Ce can be roughly described as a square antiprism. The average Ce-F distance is 2.26 Å and the average F-F distance for nearest neighbors within an antiprism is 2.77 Å. Hydrogen bonding causes this particular structure to be stabilized over the trigonal-dodecahedral arrangement found in the similar Rb2UF6 and K2ZrF6 compounds. © 1969, American Chemical Society. All rights reserved.