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E. Makovicky, D. Topa, B. Stöger:
"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";
European Journal of Mineralogy, 30 (2018), S. 149 - 164.

Abstract: 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)_{Σ 55}S₁₀₈, is monoclinic, space group: P21/c (SG#14), a 29.2691(20), b 7.8768(5), c 20.1275(15) A , b 102.065(2)°, unit-cell volume V = 4537.8(5) A^{3}. 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) A, b = 101.930(2)°, and V = 5818.6(15) A^{3} . 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 PbAs2S 4 motif. The chain motifs differ from those in the Sb-As homologues of sartorite, which display only two-fold
superstructures.

crystal structure; heptasartorite; enneasartorite; sartorite homologous series; anion-omission series; Pb-Tl-As sulfosalts; Tl substitution.

http://dx.doi.org/10.1127/ejm/2018/0030-2706