Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S160053680705475X/mg2037sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S160053680705475X/mg2037Isup2.hkl |
Iron powder (Merck, p.A.) was dissolved in half-concentrated sulfuric acid, leading to crystallization of light-blue FeSO4.7H2O after evaporation of the solvent. The heptahydrate was dehydrated in a tube furnace at 573 K for 3 h under a flowing N2/H2 (90/10) atmosphere. X-ray powder diffraction (XRPD) of the greyish powder revealed a single phase product of the low-temperature modification, α-FeSO4 (Samaras & Coing-Boyat, 1970). 0.5 g of the polycrystalline material was then mixed with 35 mg NH4Cl and heated in a sealed and evacuated silica ampoule in a temperature gradient 973 → 873 K for six days. Under these conditions NH4Cl is decomposed and the released HCl acts as the actual transport agent. After the reaction time, the ampoule was taken out of the two-zone furnace and was quenched in a cold water bath. Single crystals of β-FeSO4 with mostly plate-like habit, a colourless to light-green colour and maximal edge lengths up to 1 mm were obtained in the colder zone ("sink") of the ampoule, accompanied with a few crystals of hematite (α-Fe2O3). The remaining material at the hotter zone of the ampoule ("source") turned out to be hematite with only small amounts of β-FeSO4.
Atomic coordinates were taken from the isotypic compound MgSO4 (Weil, 2007) as starting parameters. The obtained lattice parameters of β-FeSO4 are in good agreement with those given by Kirfel et al. (1977) calculated from powder data (a = 8.715, b = 6.804, c = 4.795 Å; the latter values were transformed from the setting in Pbnm).
Data collection: CAD-4 Software (Nonius, 1989); cell refinement: CAD-4 Software (Nonius, 1989); data reduction: HELENA (implemented in PLATON; Spek, 2003); program(s) used to solve structure: coordinates taken from an isotypic structure; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).
Fig. 1. The crystal structure of β-FeSO4 projected along [001]. Displacement ellipsoids are drawn at the 90% probability level. |
FeSO4 | F(000) = 296 |
Mr = 151.91 | Dx = 3.561 Mg m−3 |
Orthorhombic, Pnma | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2n | Cell parameters from 25 reflections |
a = 8.7042 (8) Å | θ = 10.3–15.9° |
b = 6.8013 (5) Å | µ = 5.86 mm−1 |
c = 4.7868 (5) Å | T = 293 K |
V = 283.38 (4) Å3 | Plate, light green |
Z = 4 | 0.50 × 0.43 × 0.14 mm |
Nonius CAD-4 diffractometer | 875 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.024 |
Graphite monochromator | θmax = 40.0°, θmin = 4.9° |
ω/2θ scans | h = −15→15 |
Absorption correction: numerical (HABITUS; Herrendorf, 1997) | k = −12→12 |
Tmin = 0.207, Tmax = 0.736 | l = −8→8 |
6494 measured reflections | 3 standard reflections every 120 min |
922 independent reflections | intensity decay: none |
Refinement on F2 | Primary atom site location: isomorphous structure methods |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0237P)2 + 0.0945P] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.016 | (Δ/σ)max = 0.003 |
wR(F2) = 0.044 | Δρmax = 0.61 e Å−3 |
S = 1.15 | Δρmin = −0.60 e Å−3 |
922 reflections | Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
35 parameters | Extinction coefficient: 0.447 (10) |
0 restraints |
FeSO4 | V = 283.38 (4) Å3 |
Mr = 151.91 | Z = 4 |
Orthorhombic, Pnma | Mo Kα radiation |
a = 8.7042 (8) Å | µ = 5.86 mm−1 |
b = 6.8013 (5) Å | T = 293 K |
c = 4.7868 (5) Å | 0.50 × 0.43 × 0.14 mm |
Nonius CAD-4 diffractometer | 875 reflections with I > 2σ(I) |
Absorption correction: numerical (HABITUS; Herrendorf, 1997) | Rint = 0.024 |
Tmin = 0.207, Tmax = 0.736 | 3 standard reflections every 120 min |
6494 measured reflections | intensity decay: none |
922 independent reflections |
R[F2 > 2σ(F2)] = 0.016 | 35 parameters |
wR(F2) = 0.044 | 0 restraints |
S = 1.15 | Δρmax = 0.61 e Å−3 |
922 reflections | Δρmin = −0.60 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | ||
Fe | 0.0000 | 0.0000 | 0.0000 | 0.00895 (6) | |
S | 0.32185 (3) | 0.2500 | 0.02339 (4) | 0.00617 (6) | |
O1 | 0.37412 (6) | 0.07077 (8) | 0.16234 (11) | 0.01162 (10) | |
O2 | 0.15045 (9) | 0.2500 | 0.03136 (16) | 0.00953 (11) | |
O3 | 0.37783 (9) | 0.2500 | 0.73194 (15) | 0.01058 (12) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Fe | 0.00881 (8) | 0.00821 (8) | 0.00984 (8) | −0.00098 (3) | 0.00274 (3) | −0.00160 (3) |
S | 0.00547 (9) | 0.00710 (9) | 0.00596 (8) | 0.000 | −0.00039 (5) | 0.000 |
O1 | 0.0131 (2) | 0.01013 (18) | 0.01163 (19) | 0.00265 (15) | −0.00303 (15) | 0.00258 (15) |
O2 | 0.0056 (2) | 0.0089 (3) | 0.0141 (3) | 0.000 | 0.00039 (19) | 0.000 |
O3 | 0.0124 (3) | 0.0119 (3) | 0.0075 (2) | 0.000 | 0.0027 (2) | 0.000 |
Fe—O1i | 2.0111 (5) | Fe—O3i | 2.2923 (5) |
Fe—O1ii | 2.0111 (5) | S—O1iv | 1.4613 (5) |
Fe—O2iii | 2.1514 (5) | S—O1 | 1.4613 (5) |
Fe—O2 | 2.1514 (5) | S—O3v | 1.4778 (8) |
Fe—O3ii | 2.2923 (5) | S—O2 | 1.4924 (8) |
O1i—Fe—O1ii | 180.00 (4) | O3ii—Fe—O3i | 180.00 (3) |
O1i—Fe—O2iii | 94.96 (3) | O1iv—S—O1 | 113.07 (5) |
O1ii—Fe—O2iii | 85.04 (3) | O1iv—S—O3v | 109.09 (3) |
O1i—Fe—O2 | 85.04 (3) | O1—S—O3v | 109.09 (3) |
O1ii—Fe—O2 | 94.96 (3) | O1iv—S—O2 | 107.43 (3) |
O2iii—Fe—O2 | 180.0 | O1—S—O2 | 107.43 (3) |
O1i—Fe—O3ii | 92.35 (2) | O3v—S—O2 | 110.72 (4) |
O1ii—Fe—O3ii | 87.65 (2) | S—O1—Fevi | 137.31 (4) |
O2iii—Fe—O3ii | 105.67 (2) | S—O2—Fe | 127.351 (17) |
O2—Fe—O3ii | 74.33 (2) | S—O2—Fevii | 127.351 (17) |
O1i—Fe—O3i | 87.65 (2) | Fe—O2—Fevii | 104.43 (3) |
O1ii—Fe—O3i | 92.35 (2) | Sviii—O3—Fevi | 127.61 (2) |
O2iii—Fe—O3i | 74.33 (2) | Sviii—O3—Feix | 127.61 (2) |
O2—Fe—O3i | 105.67 (2) | Fevi—O3—Feix | 95.76 (3) |
Symmetry codes: (i) −x+1/2, −y, z−1/2; (ii) x−1/2, y, −z+1/2; (iii) −x, −y, −z; (iv) x, −y+1/2, z; (v) x, y, z−1; (vi) −x+1/2, −y, z+1/2; (vii) −x, y+1/2, −z; (viii) x, y, z+1; (ix) x+1/2, −y+1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | FeSO4 |
Mr | 151.91 |
Crystal system, space group | Orthorhombic, Pnma |
Temperature (K) | 293 |
a, b, c (Å) | 8.7042 (8), 6.8013 (5), 4.7868 (5) |
V (Å3) | 283.38 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 5.86 |
Crystal size (mm) | 0.50 × 0.43 × 0.14 |
Data collection | |
Diffractometer | Nonius CAD-4 diffractometer |
Absorption correction | Numerical (HABITUS; Herrendorf, 1997) |
Tmin, Tmax | 0.207, 0.736 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6494, 922, 875 |
Rint | 0.024 |
(sin θ/λ)max (Å−1) | 0.904 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.016, 0.044, 1.15 |
No. of reflections | 922 |
No. of parameters | 35 |
Δρmax, Δρmin (e Å−3) | 0.61, −0.60 |
Computer programs: CAD-4 Software (Nonius, 1989), HELENA (implemented in PLATON; Spek, 2003), coordinates taken from an isotypic structure, SHELXL97 (Sheldrick, 1997), ATOMS (Dowty, 2006).
Fe—O1i | 2.0111 (5) | S—O1 | 1.4613 (5) |
Fe—O2 | 2.1514 (5) | S—O3ii | 1.4778 (8) |
Fe—O3i | 2.2923 (5) | S—O2 | 1.4924 (8) |
Symmetry codes: (i) −x+1/2, −y, z−1/2; (ii) x, y, z−1. |
Like many other anhydrous sulfates MIISO4 (M = first row transition metal, Mg), anhydrous iron(II) sulfate is dimorphic and crystallizes in a low-temperature modification (α-form; space group Cmcm, CrVO4 structure type) and a high-temperature modification (β-form, space group Pnma, CuSO4 structure type). The refinement of the crystal structure of α-FeSO4 has already been reported (Samaras & Coing-Bayat, 1970), whereas a detailed structure determination of β-FeSO4 is still missing, although the single-crystal growth of β-FeSO4 using chemical transport reactions has been reported some time ago (Dahmen & Gruehn, 1991).
The crystal structure of β-FeSO4 contains one Fe, one S and three O atoms in the asymmetric unit. The basic structural features are [FeO4/2O2/1]∞ chains made up of edge-sharing [FeO6] octahedra and SO4 tetrahedra. The chains run parallel to [010] and are interconnected by corner-sharing with the SO4 tetrahedra into a framework structure (Fig. 1). The [FeO6] octahedron (1 point symmetry) is considerably distorted and shows a [2 + 2+2] coordination, with two short Fe—O distances to the terminal O atoms and two medium and two long distances to the bridging O atoms of the [FeO4/2O2/1]∞ chains. However, the average Fe–O distance of 2.105 Å is in good agreement with the sum of the ionic radii (2.15 Å for high-spin Fe2+; Shannon, 1976).
The SO4 tetrahedron (m point symmetry) is slightly distorted, with an average S—O bond length of 1.473 Å which is in perfect agreement with the value of 1.473 Å given by Baur (1981) for more than 100 S—O bond lengths in various sulfates(VI).
The O atoms have coordination numbers of 2 (O1) and 3 (O2, O3). O1 has one Fe and one S as neighbours, both with the shortest observed Fe—O and S—O bond lengths. O2 and O3 act as the bridging atoms in the [FeO4/2O2/1]∞ chains and thus have two Fe and one S as coordination partner.
Results from the bond valence sum (BVS) calculations (Brown, 2002), using the parameters of Brese & O'Keeffe (1991), are in accordance with the expected values (in valence units) of 2 for Fe, 6 for S and 2 for O: Fe 2.04, S 6.02, O1 2.03, O2 2.07, O3 1.93.