Rietveld refinement of the Tutton salt K₂[Fe(H₂O)₆](SO₄)₂

Dipotassium hexa­aqua­iron(II) bis­(sulfate), K₂[Fe(H₂O)₆](SO₄)₂, is a member of the isotypic series of Tutton salts with general formula M^I₂[M^II(H₂O)₆](XO₄)₂, where X = S, Se or Cr. The structure contains centrosymmetric Fe(H₂O)₆ octa­hedra, with an average Fe-O distance of 2.14 (4) Å. Each octa­hedron is surrounded by isolated SO₄ tetra­hedra [average S-O distance = 1.483 (15) Å] and distorted KO₆(H₂O)₂ polyhedra with an average K-O distance of 2.96 (15) Å. The polyhedra are linked via common O atoms and a system of medium-strength hydrogen bonds.

Key indicators

• Powder X-ray study
• T = 298 K
• Mean [sigma](S-O) = 0.014 Å
• R factor = 0.000
• wR factor = 0.000
• Data-to-parameter ratio = 0.0

checkCIF/PLATON results

No syntax errors found



Alert level C
REFI023_ALERT_1_C  _refine_diff_density_max is missing
            Maximum value of final difference map (e A-3).
            The following tests will not be performed
            DIFMN_01,DIFMX_01,DIFMX_02
REFI024_ALERT_1_C  _refine_diff_density_min is missing
            Minimum value of final difference map (e A-3).
            The following tests will not be performed
            DIFMN_01,DIFMN_02,DIFMN_03
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT128_ALERT_4_C Non-standard setting of Space group P21/c   ....    P21/a
PLAT702_ALERT_1_C Angle   Calc     89.1(4), Rep     89.9(4), Dev..       2.00 Sigma
              O6   -FE   -O7      3.555   1.555   3.555
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          2
              O4 S

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   4 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
   0 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion

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Computing details

Data collection: XRD COMMANDER (Bruker, 2004); cell refinement: TOPAS (Bruker, 2005); program(s) used to solve structure: coordinates taken from isotypic compound; program(s) used to refine structure: TOPAS; molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: TOPAS.

Dipotassium hexaaquairon(II) bis(sulfate)

Crystal data

K2[Fe(H2O)6](SO4)2	Z = 2
Mr = 434.29	F(000) = 440
Monoclinic, P21/a	Non-standard setting of space group P 21/c to adhere to reference data of other Tutton salts.
Hall symbol: -P 2yab	Dx = 2.170 Mg m^−3
a = 9.0766 (3) Å	CuKα radiation, λ = CuKα1a 1.540596 CuKα1b 1.541058 CuKα2a 1.544410 CuKα2b 1.544721 satellites 1.534753 Å
b = 12.2646 (4) Å	µ = 18.36 mm^−1
c = 6.1689 (2) Å	T = 298 K
β = 104.5478 (16)°	Particle morphology: prism
V = 664.71 (4) Å^3	pale green

Data collection

Bruker AXS D8Focus diffractometer	Scan method: step
Radiation source: sealed X-ray tube	Absorption correction: for a cylinder mounted on the φ axis Sabine et al. (1998)
Specimen mounting: borosilicate glass capillary
Data collection mode: transmission	2θmin = 5.00°, 2θmax = 155.00°, 2θstep = 0.02°

Refinement

Least-squares matrix: full	0 restraints
Rp = 5.04	0 constraints
Rwp = 6.40	H-atom parameters not refined
Rexp = 6.16	1/[Yi]
R(F^2) = 1.03	(Δ/σ)max = 0.01
7501 data points	Background function: Chebychev polynomial
Profile function: FPA (Cheary & Coelho, 1992)	Preferred orientation correction: Preferred Orientation Spherical Harmonics Order 4 y00 1 y20 -0.077(12) y22m -0.039(11) y22p -0.023(12) y40 -0.063(17) y42m -0.018(11) y42p -0.041(12) y44m -0.014(12) y44p -0.011(14)
95 parameters

Special details

Refinement. Fundamental Parameters Approach with simple axial approximation. Receiving slit 0.1 mm, divergence and antidivergence slit 0.6 mm, axial divergence 12 mm.

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

	x	y	z	Uiso*/Ueq
Fe	0	0	0	0.016 (3)
K	0.1325 (5)	0.3470 (4)	0.3443 (8)	0.033 (3)
S	0.4114 (7)	0.1356 (5)	−0.2731 (10)	0.022 (3)
O1	0.2832 (14)	0.0612 (11)	−0.379 (2)	0.026 (3)
O2	0.4111 (16)	0.2300 (11)	−0.427 (2)	0.026 (3)
O3	0.3916 (16)	0.1690 (11)	−0.051 (2)	0.026 (3)
O4	0.5533 (14)	0.0746 (10)	−0.248 (2)	0.026 (3)
O5	0.1769 (14)	0.1134 (9)	0.1698 (18)	0.017 (4)
O6	−0.1717 (13)	0.1144 (10)	0.0302 (18)	0.017 (4)
O7	0.0021 (14)	0.0695 (9)	−0.3069 (19)	0.017 (4)
H11	0.25	0.109	0.077	0.05
H12	0.234	0.096	0.319	0.05
H21	−0.132	0.185	0.073	0.05
H22	−0.281	0.114	0.001	0.05
H31	−0.032	0.141	−0.273	0.05
H32	0.113	0.071	−0.262	0.05

Geometric parameters (Å, º)

Fe—O5	2.183 (11)	K—O3^v	2.844 (13)
Fe—O5^i	2.183 (11)	K—O4^ii	3.238 (12)
Fe—O6	2.140 (12)	K—O4^iv	2.946 (15)
Fe—O6^i	2.140 (12)	K—O5	3.121 (12)
Fe—O7	2.081 (12)	K—O6^vi	2.978 (13)
Fe—O7^i	2.081 (12)	S—O1	1.493 (13)
K—O1^ii	2.731 (13)	S—O2	1.496 (15)
K—O2^iii	2.942 (13)	S—O3	1.482 (16)
K—O2^iv	2.890 (15)	S—O4	1.464 (13)
O5—Fe—O5^i	180.0	O6—Fe—O7^i	90.9 (4)
O5—Fe—O6	90.2 (4)	O6^i—Fe—O7	90.9 (5)
O5—Fe—O6^i	89.8 (4)	O6^i—Fe—O7^i	89.1 (5)
O5—Fe—O7	89.9 (4)	O7—Fe—O7^i	180.0
O5—Fe—O7^i	90.1 (4)	O1—S—O2	108.6 (7)
O5^i—Fe—O6	89.8 (4)	O1—S—O3	108.4 (6)
O5^i—Fe—O6^i	90.2 (4)	O1—S—O4	107.6 (6)
O5^i—Fe—O7	90.1 (4)	O2—S—O3	112.9 (8)
O6^i—Fe—O7^i	89.9 (4)	O2—S—O4	108.9 (6)
O6—Fe—O6^i	180.0	O3—S—O4	110.5 (7)
O6—Fe—O7	89.1 (4)

Symmetry codes: (i) −x, −y, −z; (ii) −x+1/2, y+1/2, −z; (iii) x, y, z+1; (iv) x−1/2, −y+1/2, z+1; (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
O5—H11···O3	0.98	1.82	2.73 (2)	152
O5—H12···O1^iii	0.96	1.86	2.78 (2)	162
O6—H21···O3^v	0.95	1.98	2.79 (2)	142
O6—H22···O4^vii	0.96	1.92	2.70 (1)	136
O7—H31···O2^v	0.97	1.85	2.64 (1)	137
O7—H32···O1	0.98	1.86	2.70 (1)	142

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