Elpasolite structure

Fluoride complexes of silver(III) are exemplified by the purple-red Cs2KAgF6 (elpasolite structure, octahedral Ag3+ paramagnetic with /x = 2.6/ub). Yellow MAgF4 (M = Na, Rb, K) and XeF AgF4 are diamagnetic and probably square planar [65],... 

Made by fusion, they possess the six-coordinate elpasolite structure in which the perfectly octahedral [LnCle] " ions occupy sites with cubic symmetry. These have been much studied for their optical and magnetic properties on account of this, the Ln + ions on their highly symmetrical sites having especially weak f-f transitions in their electronic spectra. Some other A2BMX6 systems also adopt the elpasolite structure. Other halide complexes like (Ph3PH)3(LnX6) and (pyH)3(LnX6) (X = Cl, Br, I) have been made by solution methods ... 

Figure 4 The cationic coordination of oxygen in the elpasolite structure (A2(12 )MVI 6 )Nf6 )06, left) and the MVI/Ni2+ ordering perpendicular to close-packed 0,A layers (right).

This review covers the series La3+ (4f°) to Lu3+ (4f14), including also Y3+, which are collectively denoted by Ln3+. It focuses upon neat and doped hex-ahalide compounds with Ln3+ situated at equilibrium sites of octahedral symmetry with the elpasolite structure, M2ALnX6 (M+, A+ are univalent cat-... 

The local Jahn-Teller effect in isolated octahedra is the subject of the next chapter. Experimental examples of Cu doped into compounds of perovskite and elpasolite structure wiU be given. In Chap. Ill the cooperative Jahn-Teller effect as the consequence of high concentrations of Jahn-TeUer centers in a solid matrix will be considered. In Chap. IV we discuss as illustrative model examples the highly interest-... 

Fig. 1. The perovskite and elpasolite structures [left perovskite unit cell (if A site empty Re03 structure) right 3-dimensional frame-work of comer-connected octahedra in the elpasolite structure]...

Fig. 7. An elementary cell of an AjBRXfi crystal with elpasolite structure.

Seifert and Yuan (1991) characterized the ABr-LaBr3 (A = Na, K, Rb, Cs) system and provided thermochemical data. The A = Na system is eutectic. The AjLaBrj (A = K, Rb, and Cs) compounds are stable at ambient temperature, but decomposed peritectically for A = Cs. At temperatures above 430°C A3LaBrg (A = Rb, Cs) crystallize in the cubic elpasolite structure common to the heavier lanthanides at ambient temperature the monoclinic K3MoClg-type structure prevailed, with A = Rb metastable. Cs2LaBr7 was stable over the limited 459 551 °C range. 

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