ISSN:
0044-2313
Keywords:
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Description / Table of Contents:
Preparation and Thermal Behaviour of Ln2CeTaO6Cl3 (Ln=La—Nd) and Ce3TaO5(OH)Cl3; Structure and Phase-Width of the Decomposition Product “La2Cex3+Ce1-x4+TaO6Cl3-x”The new mixed-valenced phases of composition Ln2Cex3+Ce1-x4+TaO6Cl3-x (Ln = La, Ce) were obtained by heating samples of oxochlorotantalates Ln2CeTaO6Cl3 (Ln = La, Ce; hex.) in evacuated silica tubes (T ≈ 1050°C). The observed thermal decomposition of Ln2CeTaO6Cl3 (Ln = La, Ce) lead to the formation of chlorine according to redox-reactions. Chemical transport experiments (T2 → T1; T2 = 1100°C, T1 = 1000°C) with chlorine as transport agent were used to prepare needle-like single crystals of the above-mentioned phases.Ln2Cex3+Ce1-x4+TaO6Cl3-x (Ln = La, Ce) crystallizes in the monoclinic space group Cm with cell-dimensions a = 35.283(6), b = 5.429(1), c = 9.517(2) Å and β = 98.92(2)° (Z = 8). The structure was refined to give R = 6.07% (Rw = 5.95%).Building units are especially chains of face-sharing Cl6-octahedra connected along [010] as well as TaO6-polyhedra with slightly distorted trigonally prismatic environment for Ta. Thus, main structures features related to the starting material La2CeTaO6Cl3 were preserved, so that the thermal decomposition can be regarded as a topotactic reaction.The model of a phase-width concerning the Cl- as well as the LaCl3-content will be discussed based on crystal structure investigations.Furthermore, the new hexagonal phase Ce3TaO5(OH)Cl3 which crystallizes in the well-known La3TaO5Cl3-type structure could be prepared by hydrogen reduction of mixed-valenced Ce3TaO6Cl3 in closed silica ampoules. The thermal behavior in air was investigated utilizing a high-temperature Guinier focusing camera. The cell-dimensions of compounds Ln3TaO5(OH)Cl3 and Ln2CeTaO6Cl3 (Ln = La—Nd) were refined and discussed.
Notes:
Durch thermischen Abbau (T ≈ 1050°C) von Oxochlorotantalaten Ln2CeTaO6Cl3 (Ln = La, Ce; hex.) entstanden unter Abspaltung von Chlor die neuen Phasen Ln2Cex3+Ce1-x4+TaO6Cl3-x (Ln = La, Ce). Einkristalle aller genannten Verbindungen wurden durch chemischen Transport (T2 → T1; T2 = 1100°C, T1 = 1000°C; Transportmittel Chlor) zugänglich. Nach der Strukturbestimmung kristallisiert La2Cex3+Ce1-x4+TaO6Cl3-x monoklin in der Raumgruppe Cm mit a = 35,283(6), b = 5,429(1), c = 9,517(2) Å, β = 98,92(2)°, Z = 8 mit R = 6,07% (Rw = 5,95%). Neben Strängen aus miteinander über Flächen verknüpften Cl6-Oktaedern enthält die Struktur TaO6-Baugruppen mit trigonal-prismatischer Koordination. Damit bleiben wesentliche Merkmale der hexagonalen Ausgangsstruktur von La2CeTaO6Cl3 erhalten, so daß der thermische Abbau zu Ln2Cex3+Ce1-x4+TaO6Cl3-x (Ln = La, Ce) auch als topotaktische Reaktion angesehen werden kann.Das Modell einer Phasenbreite bezüglich des Cl- sowie des LaCl3-Gehaltes wird auf der Grundlage detaillierter Strukturinformationen diskutiert.Ce3TaO5(OH)Cl3, eine neue, zu La3TaO5(OH)Cl3 (hex.) isostrukturelle, thermisch weniger beständige Cer3+-Verbindung konnte unter reduzierenden Bedingungen dargestellt werden. An der Luft tritt Oxydation zu Ce3TaO6Cl3 bereits bei T = 210°C ein. Die Zellparameter von Ce3TaO5(OH)Cl3 und weiteren Vertretern der Strukturfamilien Ln3TaO5(OH)Cl3 und Ln2CeTaO6Cl3 (Ln = La—Nd) werden verglichen und diskutiert.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/zaac.19905890116
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