The crystal structure of the compound Pb_6Cu~+(AsO_3)_2Cl_7 discovered in the ancient slags of Lavrion, Greece

摘要

Lead and copper(I) chloride arsenite was found in the ancient metallurgic slag from the Vrissaki area, Lavrion district, Attiki Peninsula, Greece. Its chemical composition corresponds to the idealized formula Pb_6Cu~+(AsO_3)_2Cl. The IR spectrum shows the presence of AsO_3~(3-) anions and only a trace amount of O-H bonds. The crystal structure was solved by direct methods and refined to R(F) = 0.0304 based on 1778 unique reflections with I > 2σ(I). The compound is trigonal (rhombohedral), R3, a = 9.8691(2), c = 34.2028(13) ?, V = 2885.01(14) ?~3, Z = 6. Two crystallographically nonequivalent As~(3+) cations occupy apexes of the AsO_3 pyramids. Cu+ cation occupies an apex of the CuCL, pyramid. The group [Cl_3Cu-AsO_3] is arranged along the c axis. Pb cations occupy two sites with seven- and eight-fold coordination. The crystalchemical formula of the compound is Pb_6(Cu~+Cl_3)(As~(3+)O_3)_2Cl_4.