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

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, and 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, and wR₂ = 0.0906). Both compounds feature complex frameworks of 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 a negatively charged mostly covalent framework of Pt and Pb atoms. Magnetic measurements show that the 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 coercivity.