The crystal structures of isomertieite, Pd11Sb2As2, (I) from the Monche-Tundra intrusion, Monchegorsk Igneous Complex (MIC), Kola Peninsula, Russia, and törnroosite, Pd11As2(Te1.7Bi0.3)Σ2 (IIa) and Pd11As2(Te1.3Bi0.7)Σ2 (IIb) from the South Sopcha intrusion, MIC, Kola Peninsula, Russia, were refined on the basis of X-ray diffraction data collected from single crystals. The two minerals were found to exhibit the same structure, cubic, space group Fdm, Z = 8, with unit-cell parameters for (I): a 12.297(5) Å, V 1859.3(2) Å3; for (IIa): a 12.350(2) Å, V 1883.6(4) Å3; and for (IIb): a 12.370(1) Å, V 1892.9(3) Å3. The structures were refined to R1 = 0.056 (I), 0.014 (IIa), 0.018 (IIb). The isomertieite crystal-chemical formula was confirmed. The Bi-for-Te substitution in törnroosite was found to not affect the main structural topology. In the structure of the two minerals there are three symmetrically independent Pd positions: M1, M2, and M3. M1 forms M1As4 tetrahedra, M2 forms M2As2Sb2 (I) or M2As2Te2 (II) tetrahedra, and M3 forms M3Sb3 (I) or M3Te3 (II) triangles connected together via common edges and forming a framework in the structure.
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