Erste Bestimmung von Eu-H-Abständen durch Neutronenbeugung an den neuartigen Hydriden EuMg2H6 und EuMgH4

Abstract

Trotz der hohen Neutronenabsorption von natürlichem Europium konnten die Kristallstrukturen zweier Eu‐Hydride aus Pulverdaten abgeleitet werden. EuMg2D6 kristallisiert in einem neuen AB2X6‐Strukturtyp (siehe Bild), EuMgD4 ist isotyp zu BaZnF4. Die mittleren Eu‐D‐Abstände betragen 258 bzw. 253 pm.

Synthesis, crystal structure and magnetism of the mixed metal hydrides Eu1−xSrxMg2H6 (0≤x≤0.6)

“…For Eu 2−x Sr x IrH 5 a complete solid-solution series with 0 ≤ x ≤ 2 was found [12], exhibiting the same structural phase transition due to deuterium ordering for all investigated members of the series [13]. A notable exception to this structure analogy is EuMg 2 H 6 [8] for which no strontium or other alkaline earth analogue has been found so far. The structure of this hydride is unique in the sense that it shows a novel vacancy derivative of the cubic perovskite type [8] in spite of the plethora of oxide and fluoride perovskite type variants already known [14,15].…”

“…2). The structure of that compound had been determined previously from neutron powder diffraction [8] but due to the inherent problems with the extremely high neutron absorption of natural europium the resolution of the data and thus the accuracy of the structural information was limited. Furthermore, a pseudo-symmetry, which is a frequent problem in metal hydrides, could not be excluded.…”

“…Furthermore, a pseudo-symmetry, which is a frequent problem in metal hydrides, could not be excluded. The metal substructure was refined with the program FullProf [16] using structural data published earlier [8] as starting values (Fig. 2).…”

“…The structure of this hydride is unique in the sense that it shows a novel vacancy derivative of the cubic perovskite type [8] in spite of the plethora of oxide and fluoride perovskite type variants already known [14,15]. Furthermore, its magnesium-deuterium distance of 177 pm is the shortest one ever reported in a metal hydride [8].…”

“…This is evident from isotypical pairs with A II = Eu, Sr, such as A II H 2 (PbCl 2 type [1]), A II LiH 3 [1,2] and A II PdH 3 [3,4] (cubic perovskite type), A 2 II PdH 4 (␤-K 2 SO 4 type [3,5]), A 2 II MgH 6 (K 2 GeF 6 type [6,7]), A II MgH 4 (BaZnF 4 type [8,9]), A 2 II Mg 3 H 10 (Ba 2 Ni 3 F 10 type [6,10]) and A 6 II Mg 7 H 26 (Ba 6 Zn 7 F 26 type [6,11]). For Eu 2−x Sr x IrH 5 a complete solid-solution series with 0 ≤ x ≤ 2 was found [12], exhibiting the same structural phase transition due to deuterium ordering for all investigated members of the series [13].…”