Crystal structure of Pb5(As3+O3)Cl7 from Lavrion slags

Reference:
▪ Siidra, O.I., Krivovichev, S.V., Chukanov, N.V., Pekov, I.V., Magganas, A., Katerinopoulos, A., Voudouris, P. (2011): The crystal structure of Pb5(As3+O3)Cl7 from the historic slags of Lavrion, Greece – a novel Pb(II) chloride arsenite. Mineralogical Magazine, 75, (in press).

Abstract:
The crystal structure of new lead chloride arsenite, Pb5(As3+O3)Cl7 [orthorhombic, Pbcn, a = 16.894(2), b = 10.913 (1), c = 16.760(2) Å, V = 3090.1(7) Å3], from the historic slags of Lavrion, Greece, has been solved by direct methods and refined to R1 = 0.069. The structure contains five symmetrically unique Pb, one As, eight Cl and three O sites. The As atom forms three nearly equal As–O bonds which result in the formation of an AsO3 trigonal pyramid with As at the apex. The Pb1, Pb2, Pb3 and Pb4 atoms are bonded to the AsO3 groups via Pb2+–O bonds to form complex [Pb4(AsO3)] chains parallel to the b axis. The Pb(5) atom is coordinated solely by Cl– anions. The resulting Pb(5)Cl7 polyhedra share common edges and corners to produce bent chains parallel to the c axis. A short compilation of structural features of known lead chloride arsenites is given.

I had also determined the structure of this phase (cell: 16.867, 10.908, 16.757 A, R = 2.5%, Kolitsch & Weil, unpublished data).
It was described as "R42" in Perchiazzi, N. & Rewitzer, C. (1995): Die weltbesten Barstowite und ein neues Sekundärmineral aus Lavrion, Griechenland. Lapis 20 (4), 30-31 (in German).
but with a wrong unit cell and space group.

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