Structure of the new mineral sarrabusite, Pb₅CuCl₄(SeO₃)₄, solved by manual electron-diffraction tomography

The new mineral sarrabusite Pb₅CuCl₄(SeO₃)₄ has been discovered in the Sardinian mine of Baccu Locci, near Villaputzu. It occurs as small lemon-yellow spherical aggregates of tabular crystals (< 10 µm) of less than 100 µm in diameter. The crystal structure has been solved from and refined against electron diffraction of a microcrystal. Data sets have been measured by both a manual and an automated version of the new electron-diffraction tomography technique combined with the precession of the electron beam. The sarrabusite structure is monoclinic and consists of (010) layers of straight chains formed by alternating edge-sharing CuO₄Cl₂ and PbO₈ polyhedra parallel to the c axis, which share corners laterally with two zigzag corner-sharing chains of PbO₆Cl₂ and PbO₄Cl₄ bicapped trigonal prisms. These blocks are linked together by SeO flat-pyramidal groups.

Computing details

Data collection: QED (Belletti, Calestani, Gemmi, Migliori, Ultramicroscopy, 2000, 81, 57-65); cell refinement: UNITCELL (Holland, Redfern, (1997). Mineralogical Magazine, 61, 65-77. ); program(s) used to solve structure: SIR2008 (Burla, Caliandro, Camalli, Carrozzini, Cascarano, De Caro, Giacovazzo, Polidori, Siliqi, Spagna, R (2007). J. Appl. Cryst. 40, 609-613); program(s) used to refine structure: ? Petricek, V., Dusek, M. & Palatinus L. (2006). Jana2006. Structure Determination Software Programs. Institute of Physics, Praha, Czech Republic..

(I)

Crystal data

Cl4CuO12Pb5Se4	β = 101.77 (1)°
Mr = 1749.19	V = 1912.8 (5) Å^3
Monoclinic, C2/c	Z = 4
Hall symbol: -C 2yc	F(000) = 2956
a = 24.917 (3) Å	Dx = 6.072 Mg m^−3
b = 5.506 (1) Å	Electron radiation, λ = 0.0251 Å
c = 14.242 (2) Å	T = 293 K

Data collection

FEI TECNAI F20ST diffractometer	Rint = 0.255
Radiation source: field emission electron gun	θmax = 0.8°, θmin = 0.1°
manual diffraction tomography scans	h = −27→27
2614 measured reflections	k = −6→6
915 independent reflections	l = −14→14
914 reflections with I > 3σ(I)

Refinement

Refinement on F	43 parameters
R[F^2 > 2σ(F^2)] = 0.307	0 restraints
wR(F^2) = 0.415	5 constraints
S = 26.69	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
915 reflections	(Δ/σ)max = 0.020

Special details

Experimental. Structure solved by electron diffraction data collected with manual and automated diffrraction tomography. Microscope used: manual diffraction tomography FEI TECNAI F20ST (200 kV),

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Pb1	0.1059 (3)	0.0639 (14)	0.1742 (8)	0.031 (3)*
Pb2	0.2686 (3)	0.0123 (13)	0.3721 (9)	0.031 (3)*
Pb3	0	0.562 (2)	0.25	0.031 (3)*
Se1	0.1626 (6)	1.508 (2)	0.3293 (15)	0.019 (3)*
Se2	0.0461 (6)	0.003 (2)	0.4147 (15)	0.019 (3)*
Cu1	0	0.5	0.5	0.020 (5)*
Cl1	0.2971 (11)	0.490 (4)	0.456 (3)	0.037 (5)*
Cl2	0.1203 (11)	0.507 (4)	0.534 (3)	0.037 (5)*
O1	0.1810 (15)	0.730 (7)	0.270 (4)	0.019 (4)*
O2	0.0641 (15)	0.932 (7)	0.309 (4)	0.019 (4)*
O3	0.1886 (14)	0.247 (7)	0.285 (4)	0.019 (4)*
O4	0.0067 (15)	0.263 (6)	0.382 (4)	0.019 (4)*
O5	−0.0173 (14)	0.807 (6)	0.404 (4)	0.019 (4)*
O6	0.1033 (15)	0.430 (7)	0.254 (4)	0.019 (4)*

Bond lengths (Å)

Pb1—Cl1^i	3.36 (4)	Pb3—O5	2.69 (5)
Pb1—Cl2^ii	3.16 (3)	Pb3—O5^iv	2.69 (5)
Pb1—O1^iii	2.77 (4)	Pb3—O6	2.67 (4)
Pb1—O2^iii	2.47 (5)	Pb3—O6^iv	2.67 (4)
Pb1—O3	2.54 (4)	Se1—Cl2^vii	3.29 (5)
Pb1—O4^iv	2.96 (4)	Se1—O1^vii	1.61 (5)
Pb1—O5^v	2.67 (4)	Se1—O2^vii	3.36 (4)
Pb1—O6	2.32 (4)	Se1—O3^vii	1.74 (4)
Pb2—Cl1^iii	3.14 (3)	Se1—O6^vii	1.69 (4)
Pb2—Cl1	2.91 (3)	Se2—O2^iii	1.70 (6)
Pb2—Cl1^vi	3.21 (4)	Se2—O4	1.75 (4)
Pb2—Cl2^vi	2.82 (3)	Se2—O5^iii	1.89 (4)
Pb2—O1^iii	2.83 (4)	Se2—O5^viii	3.00 (5)
Pb2—O1^i	2.85 (5)	Cu1—Cl2	2.94 (3)
Pb2—O3	2.48 (4)	Cu1—Cl2^viii	2.94 (3)
Pb2—O3^i	3.04 (5)	Cu1—O4	2.17 (5)
Pb3—O2	2.62 (4)	Cu1—O4^viii	2.17 (5)
Pb3—O2^iv	2.62 (4)	Cu1—O5	2.16 (4)
Pb3—O4	2.48 (5)	Cu1—O5^viii	2.16 (4)
Pb3—O4^iv	2.48 (5)

Symmetry codes: (i) −x+1/2, y−1/2, −z+1/2; (ii) x, −y+1, z−1/2; (iii) x, y−1, z; (iv) −x, y, −z+1/2; (v) −x, y−1, −z+1/2; (vi) −x+1/2, −y+1/2, −z+1; (vii) x, y+1, z; (viii) −x, −y+1, −z+1.