This is the first reported structure refinement of goethite, α-FeO(OH), on the basis of a single-crystal X-ray diffraction study. The structure of goethite, isostructural with diaspore, AlO(OH), and groutite, MnO(OH), can be described in terms of a slightly distorted hexagonal close-packed O-atom arrangement with Fe atoms occupying one-half of the octahedral interstices, and with all atoms located on mirror planes. There are two distinct O sites, O1 and O2, each bonded to three Fe atoms, with O2 additionally bonded to an H atom. The O2—H
O1 donor–acceptor distance in goethite is significantly longer than that in diaspore or groutite, indicating that the hydrogen bonding in goethite is the weakest of the three minerals. Analysis of refinement data for the three isostructural compounds reveals rigid-body thermal motion behavior of the octahedral groups.
Supporting information
Key indicators
- Single-crystal X-ray study
- T = 273 K
- Mean (e-O) = 0.001 Å
- R factor = 0.019
- wR factor = 0.052
- Data-to-parameter ratio = 21.0
checkCIF/PLATON results
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Alert level C
PLAT128_ALERT_4_C Non-standard setting of Space group Pnma .... Pbnm
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Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: SHELXTL (Bruker, 1997).
Crystal data top
FeO(OH) | F(000) = 172 |
Mr = 88.86 | Dx = 4.275 Mg m−3 |
Orthorhombic, Pbnm | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2c 2ab | Cell parameters from 1289 reflections |
a = 4.5979 (2) Å | θ = 2.5–40.5° |
b = 9.9510 (5) Å | µ = 10.30 mm−1 |
c = 3.0178 (1) Å | T = 273 K |
V = 138.08 (1) Å3 | Block, brown |
Z = 4 | 0.09 × 0.09 × 0.08 mm |
Data collection top
Bruker SMART APEX2 CCD area-detector diffractometer | 483 independent reflections |
Radiation source: fine-focus sealed tube | 458 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.017 |
φ and ω scans | θmax = 40.5°, θmin = 4.1° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2005) | h = −8→8 |
Tmin = 0.410, Tmax = 0.441 | k = −17→17 |
2197 measured reflections | l = −5→5 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.019 | All H-atom parameters refined |
wR(F2) = 0.052 | w = 1/[σ2(Fo2) + (0.034P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.15 | (Δ/σ)max = 0.001 |
483 reflections | Δρmax = 0.98 e Å−3 |
23 parameters | Δρmin = −1.00 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.087 (9) |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Fe | 0.04893 (4) | 0.853657 (17) | 0.2500 | 0.00588 (8) | |
O1 | 0.7057 (2) | 0.19914 (9) | 0.2500 | 0.00717 (16) | |
O2 | 0.1987 (2) | 0.05298 (9) | 0.2500 | 0.00740 (17) | |
H | 0.379 (7) | 0.082 (3) | 0.2500 | 0.017 (6)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Fe | 0.00664 (11) | 0.00537 (11) | 0.00565 (11) | 0.00004 (4) | 0.000 | 0.000 |
O1 | 0.0071 (3) | 0.0073 (3) | 0.0072 (4) | 0.0020 (3) | 0.000 | 0.000 |
O2 | 0.0069 (3) | 0.0064 (3) | 0.0089 (4) | −0.0004 (3) | 0.000 | 0.000 |
Geometric parameters (Å, º) top
Fe—O1i | 1.9325 (9) | O1—Fevii | 1.9325 (9) |
Fe—O1ii | 1.9560 (6) | O1—Feii | 1.9560 (6) |
Fe—O1iii | 1.9560 (6) | O1—Feiii | 1.9560 (6) |
Fe—O2iv | 2.0996 (9) | O2—Feviii | 2.0996 (9) |
Fe—O2v | 2.1063 (7) | O2—Fev | 2.1063 (7) |
Fe—O2vi | 2.1063 (7) | O2—Fevi | 2.1063 (7) |
| | | |
O1i—Fe—O1ii | 97.800 (13) | O1ii—Fe—O2vi | 82.98 (3) |
O1i—Fe—O1iii | 97.800 (13) | O1iii—Fe—O2vi | 169.41 (4) |
O1ii—Fe—O1iii | 100.96 (4) | O2iv—Fe—O2vi | 76.15 (3) |
O1i—Fe—O2iv | 161.87 (4) | O2v—Fe—O2vi | 91.51 (4) |
O1ii—Fe—O2iv | 93.70 (3) | Fevii—O1—Feii | 124.27 (3) |
O1iii—Fe—O2iv | 93.70 (3) | Fevii—O1—Feiii | 124.27 (3) |
O1i—Fe—O2v | 91.35 (3) | Feii—O1—Feiii | 100.96 (4) |
O1ii—Fe—O2v | 169.41 (4) | Feviii—O2—Fev | 103.85 (3) |
O1iii—Fe—O2v | 82.98 (3) | Feviii—O2—Fevi | 103.85 (3) |
O2iv—Fe—O2v | 76.15 (3) | Fev—O2—Fevi | 91.51 (4) |
O1i—Fe—O2vi | 91.35 (3) | | |
Symmetry codes: (i) −x+1/2, y+1/2, z; (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y+1, −z; (iv) x, y+1, z; (v) −x, −y+1, −z; (vi) −x, −y+1, −z+1; (vii) −x+1/2, y−1/2, z; (viii) x, y−1, z. |