Crystalline R-zirconium phosphate, Zr(HPO 4 ) 2 ‚H 2 O, was obtained by direct precipitation of soluble salts of zirconium(IV) with phosphoric acid. The fresh compound transforms, by hydrolysis, into amorphous or semicrystalline hydroxophosphates with a P/Zr molar ratio of less than two. These facts contradict the formation mechanism of zirconium phosphates admitted by researchers for over more than 40 years. The materials are characterized by chemical, textural, and thermal analysis, powder X-ray diffraction, and scanning electron microscopy.

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Microcrystals of (NH4)2Ce(PO4)2·H2O were hydrothermally obtained from a CeO2−CO(NH2)2−H3PO4−H2O system (T = 180 °C). The structure [orthorhombic, Imma, a = 6.8940(9), b = 6.8860(9), c = 17.723(2) Å] consists of CeO8 distorted dodecahedra and PO4 tetrahedra joined together to form a three-dimensional framework with small four-sided and larger six-sided tunnels in quasi-equivalent directions. Ammonium ions and water molecules are situated inside the larger tunnels. Also, the thermal decomposition is discussed.

The simultaneous intercalation of two or more n-alkylamines into R-titanium phosphate, Ti(HPO 4 ) 2 ‚H 2 O, has been investigated. The intercalation of large n-alkylamine molecules has been observed to be faster if there is a shorter alkyl chain amine, acting as a catalyst, yielding at completion single amine intercalates. New individual intercalation phases containing two different amines are obtained. In the case of a vapor mixture of several amines (C n H 2n+1 NH 2 , n ) 2-8), the compound obtained depends on the reaction time, providing selectivity. The morphology and crystallinity of the prepared materials are very sensitive to the preparation route. All synthesized phases showed monoclinic symmetry.

Microcrystals of the first ammonium-thorium phosphates, (NH 4) 2Th(PO 4) 2.H 2O (tetragonal, I4 1/ amd, a = 7.0192(4) A, c = 17.9403(8) A) and NH 4Th 2(PO 4) 3 (monoclinic, C2/ c, a = 17.880(6) A, b = 6.906(1) A, c = 8.152(2) A, beta = 104.39(2) degrees ) were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 degrees C). In both cases, the structure consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms (ThO n polyhedra, where n = 8 or 9, for the tetragonal or monoclinic phase, respectively). The ammonium ions (and water molecules) are located in the tunnels.