A commensurately modulated structure of parabutlerite, Fe^IIISO₄(OH)·2H₂O

Parabutlerite, orthorhombic Fe^IIISO₄(OH)·2H₂O, has been reinvestigated using single-crystal X-ray diffraction. The structure of parabutlerite is commensurately modulated, with a = 20.0789 (8), b = 7.4024 (7), c = 7.2294 (15) Å and q = 0.4b*. The superstructure has been determined, using a superspace approach, as having the superspace group Pnma(0β0)s0s and t₀ = 1/20, and refined to R = 0.0295 for 2392 main reflections with I > 3σ(I). The structure consists of infinite chains of Fe octahedra that are linked via vertices (OH groups); these chains are encased from both sides by SO₄ tetrahedra. The displacive modulation of atoms in parabutlerite is connected with a tilt of the chains around the b axis towards the adjacent chains due to the accommodation of an energetically more favorable hydrogen-bond geometry.

Computing details

(I)

Crystal data

FeH5O7S	Z = 8
Mr = 204.9	F(000) = 824
Orthorhombic, Pnma(0β0)s0s†	Dx = 2.534 Mg m^−3
q = 0.400000b*	Mo Kα radiation, λ = 0.71073 Å
a = 20.0789 (8) Å	µ = 3.17 mm^−1
b = 7.4024 (7) Å	T = 283 K
c = 7.2294 (15) Å	Tabular, orange
V = 1074.5 (2) Å^3	0.13 × 0.04 × 0.03 mm

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

Data collection

Oxford Diffraction CCD diffractometer	11937 independent reflections
Radiation source: X-ray tube	5550 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.027
ω scans	θmax = 28.0°, θmin = 3.2°
Absorption correction: multi-scan	h = −26→26
Tmin = 0.901, Tmax = 1	k = −5→9
31672 measured reflections	l = −9→9

Refinement

Refinement on F	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.053	All H-atom parameters refined
wR(F^2) = 0.075	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.75	(Δ/σ)max = 0.047
11937 reflections	Δρmax = 1.19 e Å^−3
280 parameters	Δρmin = −1.69 e Å^−3
8 restraints	Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
6 constraints	Extinction coefficient: 240 (90)

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

	x	y	z	Uiso*/Ueq
Fe1	0.375062 (12)	−0.00005 (3)	0.21143 (4)	0.01047 (9)
S1	0.37768 (3)	0.25	0.57746 (9)	0.01163 (18)
S2	0.37334 (3)	−0.25	−0.15860 (9)	0.01083 (18)
O1	0.33547 (9)	0.25	0.7387 (2)	0.0195 (6)
O2	0.30588 (9)	−0.25	−0.2170 (3)	0.0274 (7)
O3	0.47584 (7)	0.01074 (16)	0.2304 (2)	0.0283 (5)
O4	0.41800 (9)	−0.25	−0.3120 (3)	0.0210 (6)
O5	0.44696 (9)	0.25	0.6243 (3)	0.0282 (7)
O6	0.27525 (7)	−0.01426 (16)	0.1790 (2)	0.0272 (5)
O7	0.37696 (8)	−0.25	0.3040 (2)	0.0137 (5)
O8	0.36230 (6)	0.08811 (16)	0.46558 (18)	0.0172 (4)
O9	0.38552 (6)	−0.08887 (16)	−0.04695 (18)	0.0203 (4)
O10	0.37494 (9)	0.25	0.1178 (2)	0.0154 (5)
H1	0.2482 (6)	−0.1067 (13)	0.195 (3)	0.0326*
H2	0.2505 (6)	0.0837 (13)	0.205 (3)	0.0326*
H3	0.4994 (7)	−0.0871 (13)	0.270 (3)	0.034*
H4	0.4995 (7)	0.1063 (13)	0.268 (3)	0.034*
H5	0.3765 (12)	−0.25	0.4299 (8)	0.0165*
H6	0.3672 (12)	0.25	−0.0063 (10)	0.0185*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.01311 (16)	0.00660 (15)	0.01170 (16)	−0.00007 (9)	0.00002 (10)	−0.00089 (10)
S1	0.0147 (3)	0.0098 (3)	0.0104 (3)	0	−0.0019 (2)	0
S2	0.0123 (3)	0.0091 (3)	0.0111 (3)	0	−0.0005 (2)	0
O1	0.0317 (11)	0.0174 (10)	0.0093 (10)	0	0.0056 (8)	0
O2	0.0208 (11)	0.0241 (11)	0.0374 (15)	0	−0.0120 (10)	0
O3	0.0159 (7)	0.0219 (8)	0.0471 (10)	−0.0012 (6)	−0.0056 (7)	0.0051 (8)
O4	0.0289 (11)	0.0189 (10)	0.0151 (11)	0	0.0073 (9)	0
O5	0.0187 (10)	0.0268 (11)	0.0390 (14)	0	−0.0105 (9)	0
O6	0.0125 (7)	0.0210 (7)	0.0481 (10)	0.0003 (5)	−0.0018 (7)	−0.0078 (8)
O7	0.0256 (10)	0.0074 (8)	0.0081 (9)	0	0.0013 (8)	0
O8	0.0299 (8)	0.0105 (6)	0.0111 (7)	−0.0027 (5)	0.0004 (5)	−0.0015 (6)
O9	0.0387 (9)	0.0105 (6)	0.0118 (7)	−0.0014 (6)	0.0028 (6)	−0.0030 (6)
O10	0.0290 (11)	0.0083 (8)	0.0089 (9)	0	−0.0014 (8)	0

Bond lengths (Å)

	Average	Minimum	Maximum
Fe1—O3	2.042 (4)	2.016 (4)	2.072 (4)
Fe1—O6	2.036 (4)	2.003 (4)	2.063 (4)
Fe1—O7	1.972 (3)	1.959 (4)	1.985 (4)
Fe1—O8	1.980 (4)	1.976 (4)	1.987 (4)
Fe1—O9	1.997 (4)	1.991 (4)	2.004 (4)
Fe1—O10	1.978 (3)	1.967 (4)	1.984 (4)
S1—O1	1.450 (4)	1.434 (5)	1.457 (5)
S1—O5	1.452 (4)	1.443 (5)	1.462 (5)
S1—O8	1.490 (4)	1.482 (4)	1.509 (4)
S1—O81^i	1.490 (4)	1.478 (4)	1.501 (4)
S2—O2	1.464 (4)	1.420 (5)	1.495 (5)
S2—O4	1.446 (4)	1.429 (5)	1.463 (5)
S2—O9	1.479 (4)	1.459 (4)	1.507 (4)
S2—O91^ii	1.479 (4)	1.462 (4)	1.497 (4)
O3—H3	0.92 (3)	0.91 (3)	0.92 (3)
O3—H4	0.91 (4)	0.90 (4)	0.93 (4)
O6—H1	0.91 (3)	0.87 (4)	0.93 (4)
O6—H2	0.92 (3)	0.89 (3)	0.94 (3)
O7—H5	0.912 (12)	0.911 (16)	0.914 (16)
O7—Fe11^ii	1.972 (3)	1.955 (4)	1.986 (4)
O10—H6	0.914 (15)	0.91 (2)	0.92 (2)
O10—Fe11^i	1.978 (3)	1.971 (4)	1.987 (4)
Fe11—O31	2.042 (4)	2.017 (4)	2.070 (4)
Fe11—O61	2.036 (4)	2.001 (4)	2.059 (4)
Fe11—O81	1.980 (4)	1.974 (4)	1.985 (4)
Fe11—O91	1.997 (4)	1.988 (4)	2.002 (4)
O31—H31	0.92 (3)	0.90 (3)	0.93 (3)
O31—H41	0.91 (4)	0.89 (4)	0.92 (4)
O61—H11	0.91 (3)	0.89 (4)	0.92 (4)
O61—H21	0.92 (3)	0.90 (3)	0.93 (3)

Symmetry codes: (i) −x₁, x₂+1/2, −x₃, x₄; (ii) −x₁, x₂−1/2, −x₃, x₄.