Structure of Ag2Ce(H2O)(NO3)5and Its Thermal Decomposition Studied by Temperature-Dependent X-Ray Powder Diffraction

✍ Scribed by N. Audebrand; J.P. Auffrédic; D. Louër

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 704 KB
• Volume: 132
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7475

✦ Synopsis

The structure of Ag 2 Ce(H 2 O)(NO 3 ) 5 was determined from single-crystal diffraction. The symmetry is monoclinic (space group P2/c): a ‫؍‬ 21.472(5), b ‫؍‬ 8.027(1), c ‫؍‬ 15.413(3) A s , ‫؍‬ 90.45(2)°, V ‫؍‬ 2656.2(7) A s , Z ‫؍‬ 8. The structure consists of infinite chains of Ce icosahedra linked by nitrate groups and running along [100]. The Ag atoms and water molecules are located between these chains. Eightfold and ninefold coordinated Ag polyhedra share common vertices giving infinite chains in the three directions. Temperature-dependent X-ray powder diffraction, combined with TGA and DSC, has allowed us to completely describe the thermal decomposition process. Depending on the atmosphere, the dehydration of the precursor yields Ag 2 Ce(NO 3 ) 5 or a mixture of Ag 3 Ce 2 (NO 3 ) 9 and Ag 6 Ce(NO 3 ) 9 . Ag 2 Ce(NO 3 ) 5 is stable under vacuum in a narrow temperature range and transforms into the two previous phases. Crystalline and liquid AgNO 3 are also observed. The reaction scheme in nitrogen and vacuum is precisely described. The final product is a mixture of nanocrystalline CeO 2 and large crystals of metallic Ag. The structural relationships between the anhydrous phase and the precursor are discussed.