Crystal Chemistry of Cerium Oxyfluorides: ACe3OF11 and A2Ce3OF12 (A = K, Rb, Cs, NH4)

Autor: Joseph W. Kolis, Colin D. McMillen, Christopher C. Underwood
Rok vydání: 2015
Předmět:
Zdroj: Journal of Chemical Crystallography. 45:445-452
ISSN: 1572-8854
1074-1542
DOI: 10.1007/s10870-015-0613-z
Popis: The study of Ce4+ as a building block using CeF4 as a reagent in hydrothermal synthesis has resulted in several new cerium oxyfluorides that have been structurally characterized by single crystal X-ray diffraction. Two families of compounds are represented: ACe3OF11 (A = K, Rb, NH4), and A2Ce3OF12 (A = Cs). The ACe3OF11 compounds represent a new structure type crystallizing in space group P-6m2 with a = 7.9794(11) A and c = 8.2513(17) A for KCe3OF11, a = 8.0351(11) A and c = 8.3077(17) A for RbCe3OF11, and a = 8.0457(11) A and c = 8.2918(17) A for (NH4)Ce3OF11. The structure of Cs2Ce3OF12 conforms to the same structure type as several other A2M3OF12 (A = K, Rb, Tl; M = Hf, Zr) compounds in space group R-3m, and has unit cell parameters of a = 8.2663(12) A and c = 31.851(6) A. The two structures form different cerium oxyfluoride frameworks to accommodate the monovalent cations in different ways. Formation of the different oxyfluoride phases is thus sensitive to the size ratio of the monovalent and tetravalent cations. Synthesis of the ACe3OF11 phases has enabled a comparative analysis of the crystal chemistry across these two families of compounds, and several trends and limitations of the two structure types are identified. The hydrothermal synthesis of oxyfluorides having compositions ACe3OF11 (A = K, Rb, NH4) and A2Ce3OF12 (A = Cs) is described. Structural comparisons are made between the two structure types, and crystal chemical relationships pertaining to their preferential formation are identified based on a broader examination of their constituent monovalent and tetravalent cations. The ACe3OF11 structure type is a new structure type enabled by the size of the Ce4+ cation.
Databáze: OpenAIRE
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