Ternäre Palladiumpnictide der Erdalkali- und Seltenen Erdmetalle mit ThCr2Si2- und CaBe2Ge2-Struktur

TLDR: In this paper, 15 compounds of compositionMPd2Pn2 (M = alkaline earth or rare earth metal,Pn = As, Sb, Bi) were prepared.

Abstract: Fifteen compounds of compositionMPd2 Pn 2 (M = alkaline earth or rare earth metal,Pn = As, Sb, Bi) were prepared. TheirGuinier powder patterns show that the arsenides crystallize with the ThCr2Si2 type structure, the bismuthides with the closely related CaBe2Ge2 type structure. The antimonides most likely also have the CaBe2Ge2 structure as is demonstrated by a structure refinement of EuPd2Sb2 from single crystal X ray data (R = 0.039 for 366 independent structure factors and 15 variable parameters). The structure of SrPd2As2 (ThCr2Si2 type) was refined to a residual ofR = 0.020 for 182F values and 9 variables. EuPd2Sb2 is paramagnetic and a metallic conductor. A comparison of the cell volumes suggests intermediate valency for Eu in EuPd2As2. Chemical bonding and especially the reasons for the adoption of the ThCr2Si2 or CaBe2Ge2 type structures by these compounds are discussed. It is suggested that in going from the phosphides to the bismuthides the ThCr2Si2 structure is loosing and the CaBe2Ge2 structure is gaining stability due to decreasing Pd-Pd bonding and increasing Pd-pnictogen bonding. This trend is caused by the increasing size of the pnictogen component.