Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb₁₃Sb₇S₂₄

The structure of meneghinite (CuPb₁₃Sb₇S₂₄), from the Bottino mine in the Apuan Alps (Italy), has been solved and refined as an incommensurate structure in four-dimensional superspace. The structure is orthorhombic, superspace group Pnma(0β0)00s, cell parameters a = 24.0549 (3), b = 4.1291 (6), c = 11.3361 (16) Å, modulation vector q = 0.5433 (4)b*. The structure was refined from 6604 reflections to a final R = 0.0479. The model includes modulation of both atomic positions and displacement parameters, as well as occupational waves. The driving forces stabilizing the modulated structure of meneghinite are linked to the occupation modulation of Cu and some of the Pb atoms. As a consequence of the Cu/[] and Pb/Sb modulations, three- to sevenfold coordinations of the M cations (Pb/Sb) occur in different parts of the structure. The almost bimodal distribution of the occupation of Cu/[] and Pb/Sb at M5 conforms with the coupled substitution Sb³⁺ + [] → Pb²⁺ + Cu⁺, thus corroborating the hypothesis deduced previously for the incorporation of copper in the meneghinite structure. The very small departure (∼0.54 versus 0.50) from the commensurate value of the modulation raises the question of whether other sulfosalts considered superstructures have been properly described, and, in this light, if incommensurate modulation in sulfosalts could be much more common than thought.

Computing details

(I)

Crystal data

Cu0.966Pb13.196S24Sb6.804	V = 1126.0 (2) Å^3
Mr = 4393.3	Z = 1
Orthorhombic, Pnma(0β0)00s†	F(000) = 1839
q = 0.543300b*	Dx = 6.479 Mg m^−3
a = 24.0549 (3) Å	Mo Kα radiation, λ = 0.71073 Å
b = 4.1291 (6) Å	µ = 54.69 mm^−1
c = 11.3361 (16) Å	T = 297 K

† Symmetry operations: (1) x₁, x₂, x₃, x₄; (2) −x₁+1/2, −x₂, x₃+1/2, −x₄+1/2; (3) −x₁, x₂+1/2, −x₃, x₄+1/2; (4) x₁+1/2, −x₂+1/2, −x₃+1/2, −x₄; (5) −x₁, −x₂, −x₃, −x₄; (6) x₁+1/2, x₂, −x₃+1/2, x₄+1/2; (7) x₁, −x₂+1/2, x₃, −x₄+1/2; (8) −x₁+1/2, x₂+1/2, x₃+1/2, x₄.

Data collection

Oxford Diffraction CCD diffractometer	6604 independent reflections
Radiation source: X-ray tube	4696 reflections with I > 3σ(I)
Graphite monochromator

Refinement

Refinement on F^2	216 parameters
R[F^2 > 2σ(F^2)] = 0.048	0 restraints
wR(F^2) = 0.115	78 constraints
S = 1.97	Weighting scheme based on measured s.u.'s w = 1/(σ^2(I) + 0.0004I^2)
6604 reflections	(Δ/σ)max = 0.807

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cu1	0.247 (2)	0.25	−0.209 (5)	0.0388 (11)	0.239 (4)
Pb1	0.125229 (14)	0.25	0.15769 (3)	0.02675 (11)
Pb2	0.064759 (19)	0.75	0.46575 (4)	0.02537 (16)	0.4800 (17)
Sb2	0.064759 (19)	0.75	0.46575 (4)	0.02537 (16)	0.5199 (17)
Pb3	0.025121 (19)	0.25	−0.15251 (4)	0.02636 (16)	0.5246 (18)
Sb3	0.025121 (19)	0.25	−0.15251 (4)	0.02636 (16)	0.4754 (18)
Pb4	0.215255 (15)	0.25	0.48311 (4)	0.03405 (13)
Pb5	0.15041 (2)	0.75	−0.21855 (5)	0.02817 (16)	0.2841
Sb5	0.15041 (2)	0.75	−0.21855 (5)	0.02817 (16)	0.7159
S1	0.15229 (8)	0.75	0.33925 (19)	0.0214 (6)
S2	−0.06368 (9)	0.25	−0.02736 (18)	0.0214 (6)
S3	0.23688 (9)	0.75	−0.3373 (2)	0.0244 (6)
S4	−0.02045 (9)	0.75	−0.28375 (19)	0.0240 (6)
S5	0.10735 (9)	0.25	0.5944 (2)	0.0263 (6)
S6	0.18416 (9)	0.25	−0.0896 (2)	0.0353 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0318 (17)	0.0351 (18)	0.050 (2)	0	−0.0051 (14)	0
Pb1	0.02884 (19)	0.02372 (18)	0.0277 (2)	0	0.00114 (13)	0
Pb2	0.0275 (3)	0.0243 (3)	0.0244 (3)	0	0.00051 (18)	0
Sb2	0.0275 (3)	0.0243 (3)	0.0244 (3)	0	0.00051 (18)	0
Pb3	0.0291 (3)	0.0243 (3)	0.0257 (3)	0	0.00392 (18)	0
Sb3	0.0291 (3)	0.0243 (3)	0.0257 (3)	0	0.00392 (18)	0
Pb4	0.02498 (19)	0.0333 (2)	0.0439 (3)	0	0.00206 (15)	0
Pb5	0.0236 (3)	0.0335 (3)	0.0275 (3)	0	−0.0003 (2)	0
Sb5	0.0236 (3)	0.0335 (3)	0.0275 (3)	0	−0.0003 (2)	0
S1	0.0222 (10)	0.0230 (10)	0.0189 (10)	0	0.0000 (8)	0
S2	0.0240 (10)	0.0214 (10)	0.0188 (10)	0	0.0008 (8)	0
S3	0.0255 (10)	0.0248 (10)	0.0229 (11)	0	0.0033 (8)	0
S4	0.0252 (10)	0.0260 (10)	0.0207 (11)	0	−0.0007 (8)	0
S5	0.0273 (10)	0.0279 (11)	0.0237 (11)	0	0.0002 (8)	0
S6	0.0259 (11)	0.0552 (15)	0.0247 (12)	0	−0.0001 (9)	0

Bond lengths (Å)

	Average	Minimum	Maximum
Cu1—Pb4^i	3.22 (9)	3.14 (14)	3.32 (14)
Cu1—Pb4^ii	3.35 (8)	3.10 (11)	3.46 (11)
Cu1—Pb4^iii	3.35 (8)	3.10 (11)	3.46 (11)
Cu1—Pb5^iv	3.29 (8)	3.16 (10)	3.34 (10)
Cu1—Pb5	3.29 (8)	3.15 (10)	3.34 (10)
Cu1—S1^iii	2.41 (8)	2.39 (13)	2.45 (13)
Cu1—S3^iv	2.36 (8)	2.29 (9)	2.52 (9)
Cu1—S3	2.37 (8)	2.29 (9)	2.52 (9)
Cu1—S6	2.42 (9)	2.29 (13)	2.48 (13)
Pb1—S1^iv	2.988 (3)	2.949 (4)	3.042 (4)
Pb1—S1	2.988 (3)	2.949 (4)	3.042 (4)
Pb1—S2^v	2.939 (3)	2.859 (4)	2.987 (4)
Pb1—S2^vi	2.939 (3)	2.859 (4)	2.987 (4)
Pb1—S4^v	2.901 (4)	2.891 (6)	2.907 (6)
Pb2—Pb2^vii	3.7609 (11)	3.7302 (13)	3.9507 (13)
Pb2—Pb2^viii	3.7626 (11)	3.7302 (13)	3.9506 (13)
Pb2—Sb2	0	0	0
Pb2—S1	2.587 (3)	2.445 (6)	2.673 (6)
Pb2—S4^v	3.044 (4)	2.890 (5)	3.342 (5)
Pb2—S4^vi	3.045 (4)	2.890 (5)	3.337 (5)
Pb2—S5	2.802 (4)	2.496 (4)	2.983 (4)
Pb2—S5^ix	2.803 (4)	2.490 (4)	2.983 (4)
Sb2—S1	2.529 (3)	2.411 (6)	2.660 (6)
Sb2—S5	2.684 (4)	2.427 (4)	2.982 (4)
Sb2—S5^ix	2.686 (4)	2.427 (4)	2.983 (4)
Pb3—Sb3	0	0	0
Pb3—Pb5^iv	3.6940 (11)	3.6708 (13)	3.7470 (13)
Pb3—Pb5	3.6944 (11)	3.6708 (13)	3.7480 (13)
Pb3—S2	2.597 (3)	2.462 (6)	2.680 (6)
Pb3—S2^v	3.010 (3)	2.936 (4)	3.199 (4)
Pb3—S2^vi	3.010 (3)	2.936 (4)	3.200 (4)
Pb3—S4^iv	2.838 (4)	2.517 (4)	3.013 (4)
Pb3—S4	2.838 (4)	2.520 (4)	3.013 (4)
Sb3—S2	2.544 (3)	2.438 (6)	2.665 (6)
Sb3—S4^iv	2.717 (4)	2.452 (4)	2.993 (4)
Sb3—S4	2.717 (4)	2.452 (4)	2.994 (4)
Pb4—S1^iv	3.037 (3)	2.890 (4)	3.137 (4)
Pb4—S1	3.037 (3)	2.890 (4)	3.136 (4)
Pb4—S3^x	2.948 (4)	2.830 (4)	3.076 (4)
Pb4—S3^xi	2.947 (4)	2.830 (4)	3.076 (4)
Pb4—S5	2.893 (4)	2.843 (6)	2.953 (6)
Pb5—Sb5	0	0	0
Pb5—S3	2.519 (4)	2.429 (6)	2.596 (6)
Pb5—S5^i	3.047 (4)	2.894 (5)	3.284 (5)
Pb5—S5^xii	3.045 (4)	2.894 (5)	3.280 (5)
Pb5—S6	2.781 (4)	2.532 (5)	2.996 (5)
Pb5—S6^ix	2.780 (4)	2.529 (5)	2.996 (5)
Sb5—S3	2.481 (4)	2.419 (6)	2.596 (6)
Sb5—S6	2.658 (4)	2.411 (5)	2.996 (5)
Sb5—S6^ix	2.658 (4)	2.411 (5)	2.996 (5)

Symmetry codes: (i) x₁, x₂, x₃−1, x₄; (ii) −x₁+1/2, −x₂, x₃−1/2, −x₄+1/2; (iii) −x₁+1/2, −x₂+1, x₃−1/2, −x₄+1/2; (iv) x₁, x₂−1, x₃, x₄; (v) −x₁, x₂−1/2, −x₃, x₄+1/2; (vi) −x₁, x₂+1/2, −x₃, x₄+1/2; (vii) −x₁, x₂−1/2, −x₃+1, x₄+1/2; (viii) −x₁, x₂+1/2, −x₃+1, x₄+1/2; (ix) x₁, x₂+1, x₃, x₄; (x) x₁, x₂−1, x₃+1, x₄; (xi) x₁, x₂, x₃+1, x₄; (xii) x₁, x₂+1, x₃−1, x₄.