Acta Cryst. (2012). B68, 480-492 [ doi:10.1107/S0108768112034027 ]
Abstract: The crystal structures of two very close, but distinct complex minerals of the lead sulfosalt group have been solved: sterryite, Cu(Ag,Cu)3Pb19(Sb,As)22(As-As)S56, and parasterryite, Ag4Pb20(Sb,As)24S58. They are analyzed and compared according to modular analysis. The fundamental building block is a complex column centred on a Pb6S12 triangular prismatic core, with two additional long and short arms. The main chemical and topological differences relate to the short arm, which induces a relative a/4 shift ( 2 Å along the elongation parameter) of the constitutive rod layers, as illustrated by distinct cell settings within the same space group (P21/n and P21/c, respectively). Selection of the shortest (i.e. strongest) (Sb,As)-S bonds permitted to enhance the polymeric organization of (Sb,As) atoms with triangular pyramidal coordination. These two quasi-homeotypic structures are expanded derivatives of owyheeite, Ag3Pb10Sb11S28. The hierarchy of organization levels from zero- to three-dimensional entities is subordinated to building operators, which appear as the driving force for the construction of such complex structures. Minor cations (Ag, Cu) or the As-As pair in sterryite secure the final locking, which favours the formation of one or the other compound.
Keywords: modular analysis; complex sulfosalt structures; sterryite; parasterryite; owyheeite derivative.
Structure factor file (CIF format) (1086.6 kbytes)
Structure factor file (CIF format) (1726.3 kbytes)
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