ИСТИНА

The Pd5TlAs structure type was first reported by El-Boragy et al. † Pd5TlAs is built from alternating layers of face-sharing thallium-centered palladium cuboctahedra and flat arsenic atom layers along the c axis. The paper by El-Boragy et al lists many palladium- and platinum-based compounds as crystallizing within this type. However, no information about these compounds, apart from the unit cell metrics often deduced from the multiphase samples, has been given. Here we present the synthesis and investigations of a series of the palladiumand platinum-rich mixed phosphides and selenides belonging to the Pd5TlAs structure type, including Pd5InP, Pt5InP, Pd5ZnP, Pt5ZnP, and Pd5ZnSe. We have succeeded in obtaining either phase-pure samples, or samples with minimal amount of binary impurities, and for some of the compounds we even obtained single crystals. The structures were refined based on either powder or single-crystal data. The noticeable trend is that the compounds of the Pd5TlAs are more abundant for phosphorus and arsenic, while the chalcogen-containing ones are relatively rare and, in fact, are limited to a few selenium-containing ones. We also present a detailed crystallographic analysis of the structures in the series, most importantly, the distortions of cuboctahedra upon the formation of the compounds, as well as details of the electronic structure and bonding analysis based on the DFT calculations. The possibilities of the formation of the homological series are also discussed, based on our search for the compounds of the Pd8M2Q- and Pt8M2Q-type (M=In, Zn; Q=P, As, Se) which can be considered a second homologue in the series after the Pd5TlAs-type compounds. _____________________________________________ ∗ This work was supported by RSF (Russian Science Foundation) , grant No. 17-73-10492 † M. El-Boragy, K. Schubert. Z. Metallkde, 1970, 61(8), 579.