The crystal structures of heptasartorite, Tl₇Pb₂₂As₅₅S₁₀₈, and enneasartorite, Tl₆Pb₃₂As₇₀S₁₄₀, two members of an anion-omission series of complex sulfosalts from Lengenbach, the Swiss Alps, and comparison with the structures of As–Sb sartorite homologues

Crystal structures of heptasartorite and enneasartorite, two members of the sartorite anion-omission series were refined from the material from the Lengenbach deposit, Swiss Alps. Heptasartorite, Tl₇Pb₂₂(As₅₄Sb)_Σ55S₁₀₈, is monoclinic, space group: P2₁/c (SG#14), a 29.2691(20), b 7.8768(5), c 20.1275(15) Å, β 102.065(2)°, unit-cell volume V = 4537.8(5) ų. Enneasartorite, Tl₆Pb₃₂As₇₀S₁₄₀, is monoclinic, space group P2₁/c (SG#14), and lattice parameters a = 37.612(6), b = 7.8777(12), c = 20.071(3) Å, β = 101.930(2)°, and V = 5818.6(15) ų. Both structures are typical structures of an N = 3 homologue of the sartorite homologous series with zig-zag walls of (Pb, Tl) trigonal coordination prisms separating (primarily) As-based slabs of structure configured to accommodate lone electron pairs of As. The sevenfold superstructure of heptasartorite is based on a sequence of crankshaft chains: on a surface of a fundamental double-ribbon in the As-rich structure slab one can recognize a W-shaped chain with five As and one mixed coordination polyhedron in which As and a large cation combine, a 4-member chain, a pair of As polyhedra, and two isolated As polyhedra. In the here redetermined structure of enneasartorite, one more 4-member chain of As polyhedra has been added, making the environment of the W-shaped chain symmetric. One of the isolated As polyhedra became a mixed-cation site. In both structures, the S site chelated by the As atoms of the W chain becomes vacant, generating the anion-omission derivatives of the ideal PbAs₂S₄ motif. The chain motifs differ from those in the Sb–As homologues of sartorite, which display only two-fold superstructures.