(NH4)2[PR(NO3)5(H2O)2].2H2O, CRYSTAL-STRUCTURE AND THERMAL-BEHAVIOR

In the crystal structure of (NH4)2[Pr(NO3)5(H2O)2].2H2O (monoclinic, C2/c, Z = 4; a = 1104.7(5); b = 892.8(3); c = 1787.5(8) pm; beta = 101.78(7)degrees) Pr3+ exhibits a coordination number of twelve (five bidentate nitrate and two water molecules as ligands). The structure may be viewed at as a layer structure: Slabs of the composition [Pr(NO3)5]2- and [(NH4)2(H2O)2(H2O)2]2+ are stacked in the [100] direction. The thermal decomposition consists of six steps where (NH4)2(Pr(NO3)5(H2O)2], (NH4)2[Pr(NO3)5], (NH4)[Pr(NO3)4], Pr(NO3)3, and PrONO3 are formed as intermediates judging from simultaneous TG/DTA-MS investigations. The final product is PrO2-x (CaF2-type). High Resolution Transmission Electron Microscopy shows that it is produced as highly ordered agglomerates of crystallites of the size 10-50 nm.