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Single crystals of the high-temperature modification of iron(II) sulfate, β-FeSO4, were grown using chemical transport reactions with HCl as transport agent. The title compound crystallizes in the CuSO4 structure (space group Pnma) and is isotypic with other divalent metal sulfates MIISO4 adopting this structure type (M = Mg, Co, Zn). The coordination polyhedron of the Fe2+ cation is a distorted octa­hedron (\overline{1} symmetry) with a [2+2+2] distribution of bond lengths. By edge-sharing of the [FeO6] octa­hedra, [FeO4/2O2/1] chains are established parallel to [010]; these are linked into a framework by corner-sharing with slightly distorted SO4 tetra­hedra (m symmetry).

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S160053680705475X/mg2037sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S160053680705475X/mg2037Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](S-O) = 0.001 Å
  • R factor = 0.016
  • wR factor = 0.044
  • Data-to-parameter ratio = 26.3

checkCIF/PLATON results

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Alert level G ABSTM02_ALERT_3_G The ratio of expected to reported Tmax/Tmin(RR) is > 1.50 Tmin and Tmax reported: 0.207 0.735 Tmin and Tmax expected: 0.066 0.430 RR = 1.840 Please check that your absorption correction is appropriate. PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature 293 K PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature . 293 K PLAT794_ALERT_5_G Check Predicted Bond Valency for Fe (2) 2.04
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 0 ALERT level C = Check and explain 4 ALERT level G = General alerts; check 2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 0 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 1 ALERT type 5 Informative message, check

Comment top

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.

Related literature top

For single-crystal growth of β-FeSO4 using chemical transport reactions, see: Dahmen & Gruehn (1991). Lattice parameters of this polymorph were reported by Kirfel et al. (1977). The structure of the α-FeSO4 polymorph was determined by Samaras & Coing-Boyat (1970). For the isotypic MgSO4, see: Weil (2007). For the bond-valence model, see: Brown (2002) and Brese & O'Keeffe (1991). Average S—O distances were calculated by Baur (1981) and ionic radii were taken from Shannon (1976).

Experimental top

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.

Refinement top

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).

Computing details top

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).

Figures top
[Figure 1] Fig. 1. The crystal structure of β-FeSO4 projected along [001]. Displacement ellipsoids are drawn at the 90% probability level.
Iron(II) sulfate top
Crystal data top
FeSO4F(000) = 296
Mr = 151.91Dx = 3.561 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2nCell parameters from 25 reflections
a = 8.7042 (8) Åθ = 10.3–15.9°
b = 6.8013 (5) ŵ = 5.86 mm1
c = 4.7868 (5) ÅT = 293 K
V = 283.38 (4) Å3Plate, light green
Z = 40.50 × 0.43 × 0.14 mm
Data collection top
Nonius CAD-4
diffractometer
875 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.024
Graphite monochromatorθmax = 40.0°, θmin = 4.9°
ω/2θ scansh = 1515
Absorption correction: numerical
(HABITUS; Herrendorf, 1997)
k = 1212
Tmin = 0.207, Tmax = 0.736l = 88
6494 measured reflections3 standard reflections every 120 min
922 independent reflections intensity decay: none
Refinement top
Refinement on F2Primary 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) = 0.044Δρmax = 0.61 e Å3
S = 1.15Δρmin = 0.60 e Å3
922 reflectionsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
35 parametersExtinction coefficient: 0.447 (10)
0 restraints
Crystal data top
FeSO4V = 283.38 (4) Å3
Mr = 151.91Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 8.7042 (8) ŵ = 5.86 mm1
b = 6.8013 (5) ÅT = 293 K
c = 4.7868 (5) Å0.50 × 0.43 × 0.14 mm
Data collection top
Nonius CAD-4
diffractometer
875 reflections with I > 2σ(I)
Absorption correction: numerical
(HABITUS; Herrendorf, 1997)
Rint = 0.024
Tmin = 0.207, Tmax = 0.7363 standard reflections every 120 min
6494 measured reflections intensity decay: none
922 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01635 parameters
wR(F2) = 0.0440 restraints
S = 1.15Δρmax = 0.61 e Å3
922 reflectionsΔρmin = 0.60 e Å3
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
xyzUiso*/Ueq
Fe0.00000.00000.00000.00895 (6)
S0.32185 (3)0.25000.02339 (4)0.00617 (6)
O10.37412 (6)0.07077 (8)0.16234 (11)0.01162 (10)
O20.15045 (9)0.25000.03136 (16)0.00953 (11)
O30.37783 (9)0.25000.73194 (15)0.01058 (12)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe0.00881 (8)0.00821 (8)0.00984 (8)0.00098 (3)0.00274 (3)0.00160 (3)
S0.00547 (9)0.00710 (9)0.00596 (8)0.0000.00039 (5)0.000
O10.0131 (2)0.01013 (18)0.01163 (19)0.00265 (15)0.00303 (15)0.00258 (15)
O20.0056 (2)0.0089 (3)0.0141 (3)0.0000.00039 (19)0.000
O30.0124 (3)0.0119 (3)0.0075 (2)0.0000.0027 (2)0.000
Geometric parameters (Å, º) top
Fe—O1i2.0111 (5)Fe—O3i2.2923 (5)
Fe—O1ii2.0111 (5)S—O1iv1.4613 (5)
Fe—O2iii2.1514 (5)S—O11.4613 (5)
Fe—O22.1514 (5)S—O3v1.4778 (8)
Fe—O3ii2.2923 (5)S—O21.4924 (8)
O1i—Fe—O1ii180.00 (4)O3ii—Fe—O3i180.00 (3)
O1i—Fe—O2iii94.96 (3)O1iv—S—O1113.07 (5)
O1ii—Fe—O2iii85.04 (3)O1iv—S—O3v109.09 (3)
O1i—Fe—O285.04 (3)O1—S—O3v109.09 (3)
O1ii—Fe—O294.96 (3)O1iv—S—O2107.43 (3)
O2iii—Fe—O2180.0O1—S—O2107.43 (3)
O1i—Fe—O3ii92.35 (2)O3v—S—O2110.72 (4)
O1ii—Fe—O3ii87.65 (2)S—O1—Fevi137.31 (4)
O2iii—Fe—O3ii105.67 (2)S—O2—Fe127.351 (17)
O2—Fe—O3ii74.33 (2)S—O2—Fevii127.351 (17)
O1i—Fe—O3i87.65 (2)Fe—O2—Fevii104.43 (3)
O1ii—Fe—O3i92.35 (2)Sviii—O3—Fevi127.61 (2)
O2iii—Fe—O3i74.33 (2)Sviii—O3—Feix127.61 (2)
O2—Fe—O3i105.67 (2)Fevi—O3—Feix95.76 (3)
Symmetry codes: (i) x+1/2, y, z1/2; (ii) x1/2, y, z+1/2; (iii) x, y, z; (iv) x, y+1/2, z; (v) x, y, z1; (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 formulaFeSO4
Mr151.91
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)293
a, b, c (Å)8.7042 (8), 6.8013 (5), 4.7868 (5)
V3)283.38 (4)
Z4
Radiation typeMo Kα
µ (mm1)5.86
Crystal size (mm)0.50 × 0.43 × 0.14
Data collection
DiffractometerNonius CAD-4
diffractometer
Absorption correctionNumerical
(HABITUS; Herrendorf, 1997)
Tmin, Tmax0.207, 0.736
No. of measured, independent and
observed [I > 2σ(I)] reflections
6494, 922, 875
Rint0.024
(sin θ/λ)max1)0.904
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.016, 0.044, 1.15
No. of reflections922
No. of parameters35
Δρmax, Δρmin (e Å3)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).

Selected bond lengths (Å) top
Fe—O1i2.0111 (5)S—O11.4613 (5)
Fe—O22.1514 (5)S—O3ii1.4778 (8)
Fe—O3i2.2923 (5)S—O21.4924 (8)
Symmetry codes: (i) x+1/2, y, z1/2; (ii) x, y, z1.
 

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