Refinement of cronstedtite-1M

The structure of cronstedtite-1M was refined using a crystal from Eisleben (Saxony-Anhalt, Germany). The space group is Cm, a = 5.5033 (3), b = 9.5289 (6), c = 7.3328 (5) Å, β = 104.493 (7)°, composition (Fe²⁺_2.461Fe³⁺_0.539)(Si_1.461Fe³⁺_0.539)O₅(OH)₄, Z = 2. Despite diffusely streaked characteristic polytype reflections, the refinement converged to R_obs = 0.0242 for 1117 independent reflections. Separate R_obs values of 0.0183 and 0.0553 were obtained for 415 subfamily and 702 characteristic reflections, respectively. The structure is built of one edge-sharing octahedral (Oc) and one corner-sharing tetrahedral (Tet) sheet forming the 1:1 layer by sharing apical corners of the Tet sheet. Consecutive layers are shifted by a/3 of the hexagonal cell, the polytype belongs to the subfamily (Bailey's group) A. There are two octahedral sites M1 (at m), M2 (in a general position) both fully occupied by Fe. Since the M2 octahedron is larger than M1, the Oc sheet is meso-octahedral. The Tet sheet contains one tetrahedral position, T1, occupied by Si and Fe in the ratio 0.731:0.269 (9). The ring of tetrahedra is strongly ditrigonalized, α = +12.7°; Franzini type A. Of three H atoms localized, two are involved in hydrogen bonds, linking OH groups of the Oc sheet with basal O atoms of the Tet sheet. The basal O atoms (acceptors) of the Tet sheet are rotated close to OH groups (donors) of the Oc sheet of an adjacent layer in order to achieve reasonable lengths and geometries of hydrogen bonds. The structure is interpreted as an example of the order–disorder (OD) structure of more than one kind of layer with a very low degree of desymmetrization.

S1. Experimental

S1.1. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1.

S2. Results and discussion

Computing details

Data collection: CrysAlis PRO, Agilent Technologies, Version 1.171.37.31 (release 14-01-2014 CrysAlis171 .NET) (compiled Jan 14 2014,18:38:05); cell refinement: CrysAlis PRO, Agilent Technologies, Version 1.171.37.31 (release 14-01-2014 CrysAlis171 .NET) (compiled Jan 14 2014,18:38:05); data reduction: CrysAlis PRO, Agilent Technologies, Version 1.171.37.31 (release 14-01-2014 CrysAlis171 .NET) (compiled Jan 14 2014,18:38:05).

Figures

(I)

Crystal data

Fe3.539H4O9Si1.461	F(000) = 377
Mr = 386.7	Dx = 3.448 Mg m^−3
Monoclinic, Cm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2y	Cell parameters from 1042 reflections
a = 5.5033 (3) Å	θ = 4.2–30.3°
b = 9.5289 (5) Å	µ = 7.04 mm^−1
c = 7.3328 (5) Å	T = 293 K
β = 104.493 (6)°	Plate, black
V = 372.30 (4) Å^3	0.25 × 0.15 × 0.10 mm
Z = 2

Data collection

Xcalibur, Atlas, Gemini ultra diffractometer	1117 independent reflections
Radiation source: X-ray tube	999 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.020
Detector resolution: 10.3784 pixels mm^-1	θmax = 30.9°, θmin = 2.9°
ω scans	h = −7→7
Absorption correction: multi-scan CrysAlis PRO, Agilent Technologies, Version 1.171.37.31 (release 14-01-2014 CrysAlis171 .NET) (compiled Jan 14 2014,18:38:05) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	k = −12→13
Tmin = 0.554, Tmax = 1	l = −10→10
2993 measured reflections

Refinement

Refinement on F	14 constraints
R[F^2 > 2σ(F^2)] = 0.024	All H-atom parameters refined
wR(F^2) = 0.035	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.64	(Δ/σ)max = 0.019
1117 reflections	Δρmax = 0.62 e Å^−3
77 parameters	Δρmin = −0.37 e Å^−3
3 restraints	Absolute structure: 533 of Friedel pairs used in the refinement

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Fem1	0.25	0.5	0.6	0.0116 (3)
Fem2	0.2516 (2)	0.16754 (7)	0.59589 (16)	0.01178 (17)
Sit1	0.4519 (2)	0.16619 (8)	0.19842 (17)	0.0091 (3)	0.731 (9)
Fet1	0.4519 (2)	0.16619 (8)	0.19842 (17)	0.0091 (3)	0.269 (9)
O1	−0.0109 (11)	0.5	0.1200 (7)	0.0302 (19)
O2	0.1426 (8)	0.2172 (4)	0.1208 (5)	0.0310 (13)
O4	0.5371 (7)	0.1633 (3)	0.4448 (5)	0.0164 (11)
Oh1	0.5279 (10)	0.5	0.4467 (7)	0.0163 (16)
Oh2	−0.0335 (11)	0.5	0.7365 (7)	0.0146 (17)
Oh3	0.4631 (8)	0.3357 (3)	0.7374 (5)	0.0145 (11)
H1	0.493 (14)	0.5	0.319 (3)	0.0195*
H2	0.005 (14)	0.5	0.863 (3)	0.0175*
H3	0.507 (10)	0.334 (5)	0.863 (3)	0.0174*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fem1	0.0093 (4)	0.0093 (4)	0.0174 (5)	0	0.0053 (4)	0
Fem2	0.0091 (3)	0.0085 (3)	0.0187 (3)	−0.0001 (3)	0.0053 (2)	0.0001 (3)
Sit1	0.0090 (4)	0.0102 (4)	0.0081 (5)	−0.0005 (11)	0.0023 (3)	−0.0008 (9)
Fet1	0.0090 (4)	0.0102 (4)	0.0081 (5)	−0.0005 (11)	0.0023 (3)	−0.0008 (9)
O1	0.033 (3)	0.035 (3)	0.023 (3)	0	0.006 (2)	0
O2	0.030 (2)	0.036 (2)	0.027 (2)	0.0011 (19)	0.0070 (18)	0.0003 (18)
O4	0.0156 (17)	0.0170 (19)	0.0171 (17)	−0.0008 (14)	0.0046 (16)	−0.0008 (13)
Oh1	0.016 (2)	0.017 (3)	0.016 (2)	0	0.004 (2)	0
Oh2	0.015 (2)	0.014 (2)	0.015 (3)	0	0.006 (3)	0
Oh3	0.0137 (17)	0.0137 (18)	0.016 (2)	−0.0013 (16)	0.0034 (17)	0.0003 (13)

Geometric parameters (Å, º)

Fem1—O4^i	2.103 (3)	Fem2—Oh3	2.096 (3)
Fem1—O4^ii	2.103 (3)	Fem2—Oh3^ii	2.103 (5)
Fem1—Oh1	2.112 (6)	Sit1—O1^v	1.714 (2)
Fem1—Oh2	2.054 (6)	Sit1—O2	1.724 (4)
Fem1—Oh3	2.061 (3)	Sit1—O2^vi	1.721 (5)
Fem1—Oh3^iii	2.061 (3)	Sit1—O4	1.750 (4)
Fem2—O4	2.137 (4)	Oh1—H1	0.91 (2)
Fem2—O4^ii	2.136 (3)	Oh2—H2	0.90 (2)
Fem2—Oh1^iv	2.142 (3)	Oh3—H3	0.89 (2)
Fem2—Oh2^v	2.098 (3)
O4^i—Fem1—O4^ii	95.47 (12)	O4—Fem2—Oh3	83.22 (15)
O4^i—Fem1—Oh1	95.26 (14)	O4—Fem2—Oh3^ii	177.50 (13)
O4^i—Fem1—Oh2	82.84 (14)	O4^ii—Fem2—Oh1^iv	97.19 (13)
O4^i—Fem1—Oh3	176.58 (15)	O4^ii—Fem2—Oh2^v	178.1 (2)
O4^i—Fem1—Oh3^iii	82.78 (13)	O4^ii—Fem2—Oh3	81.15 (13)
O4^ii—Fem1—Oh1	95.26 (14)	O4^ii—Fem2—Oh3^ii	83.08 (15)
O4^ii—Fem1—Oh2	82.84 (14)	Oh1^iv—Fem2—Oh2^v	82.24 (14)
O4^ii—Fem1—Oh3	82.78 (13)	Oh1^iv—Fem2—Oh3	178.33 (14)
O4^ii—Fem1—Oh3^iii	176.58 (15)	Oh1^iv—Fem2—Oh3^ii	80.35 (18)
Oh1—Fem1—Oh2	177.16 (17)	Oh2^v—Fem2—Oh3	99.42 (14)
Oh1—Fem1—Oh3	82.01 (14)	Oh2^v—Fem2—Oh3^ii	98.5 (2)
Oh1—Fem1—Oh3^iii	82.01 (14)	Oh3—Fem2—Oh3^ii	99.28 (16)
Oh2—Fem1—Oh3	99.81 (15)	O1^v—Sit1—O2	109.9 (2)
Oh2—Fem1—Oh3^iii	99.81 (15)	O1^v—Sit1—O2^vi	110.6 (3)
Oh3—Fem1—Oh3^iii	98.81 (13)	O1^v—Sit1—O4	107.9 (2)
O4—Fem2—O4^ii	97.36 (15)	O2—Sit1—O2^vi	110.0 (2)
O4—Fem2—Oh1^iv	97.15 (18)	O2—Sit1—O4	109.4 (2)
O4—Fem2—Oh2^v	80.98 (19)	O2^vi—Sit1—O4	108.90 (18)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
Oh2—H2···O1^vii	0.90 (2)	1.91 (3)	2.784 (7)	164 (7)
Oh3—H3···O2^viii	0.89 (2)	1.91 (2)	2.782 (5)	165 (5)

Symmetry codes: (vii) x, y, z+1; (viii) x+1/2, −y+1/2, z+1.