Eu2Pt3Pb5 and SrPt2Pb4 — lead-based intermetallics with Y2Rh3Sn5 / NdRh2Sn4-type polyanionic platinum-lead 3D frameworks

Abstract

Two platinide plumbides, Eu2Pt3Pb5 and SrPt2Pb4, were discovered using high-temperature exploratory synthesis and flux-assisted crystal growth. Their crystal structures were determined from single-crystal X-ray diffraction. Both compounds crystallize in the orthorhombic system, Eu2Pt3Pb5 belongs to the Y2Rh3Sn5 structure type (Cmc21, a=4.6146(2) Å, b=27.3082(12) Å, c=7.5147(3) Å, Z=4, R1=0.0310, wR2=0.0736) and SrPt2Pb4 to the NdRh2Sn4 type (Pnma, a=19.411(5) Å, b=4.5834(13) Å, c=7.6548(19) Å, Z=4, R1=0.0399, wR2=0.0906). Both compounds feature complex frameworks of the Pt-Pb and Pb-Pb bonds with very similar motifs, with Eu or Sr cations filling the cavities, which differ by the presence of the TiNiSi-type EuPtPb layer in Eu2Pt3Pb5. According to the DFT calculations, both compounds are metallic and feature Sr and Eu divalent cations along with negatively charged mostly covalent framework of Pt and Pb atoms. Magnetic measurements show that SrPt2Pb4 compound is non-magnetic, while Eu2Pt3Pb5 is a paramagnet above ca. 85 K and below that temperature transitions to the ferromagnetically ordered state with very low coercitivity.