The crystal structure of the mineral polyhalite, or dipotassium dicalcium magnesium tetrakis[sulfate(VI)] dihydrate, was reinvestigated by means of single-crystal X-ray diffraction data. The structural model previously reported was confirmed, although a higher precision of the refinement has been achieved. The structure consists of K[11] and Ca[8] polyhedra and [MgO4(H2O)2] octahedra sharing edges and faces; SO4 tetrahedra share edges with the polyhedra.
Supporting information
Key indicators
- Single-crystal X-ray study
- T = 298 K
- Mean (Wave) = 0.000 Å
- H-atom completeness 1%
- R factor = 0.048
- wR factor = 0.143
- Data-to-parameter ratio = 12.3
checkCIF/PLATON results
No syntax errors found
Alert level G
FORMU01_ALERT_2_G There is a discrepancy between the atom counts in the
_chemical_formula_sum and the formula from the _atom_site* data.
Atom count from _chemical_formula_sum:H4 Ca2 K2 Mg1 O18 S4
Atom count from the _atom_site data: Ca2 K2 Mg1 O18 S4
CELLZ01_ALERT_1_G Difference between formula and atom_site contents detected.
CELLZ01_ALERT_1_G WARNING: H atoms missing from atom site list. Is this intentional?
From the CIF: _cell_formula_units_Z 1
From the CIF: _chemical_formula_sum Ca2 H4 K2 Mg1 O18 S4
TEST: Compare cell contents of formula and atom_site data
atom Z*formula cif sites diff
Ca 2.00 2.00 0.00
H 4.00 0.00 4.00
K 2.00 2.00 0.00
Mg 1.00 1.00 0.00
O 18.00 18.00 0.00
S 4.00 4.00 0.00
0 ALERT level A = In general: serious problem
0 ALERT level B = Potentially serious problem
0 ALERT level C = Check and explain
3 ALERT level G = General alerts; check
2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
1 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
0 ALERT type 4 Improvement, methodology, query or suggestion
Data collection: CrysAlis CCD (Oxford Diffraction, 2002); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Xtal–DRAW (Downs & Hall-Wallace, 2003) and ORTEP-3 for Windows
(Farrugia, 1997); software used to prepare material for publication: SHELXL97.
Dipotassium Dicalcium Magnesium Tetrakis[sulfate(VI)] Dihydrate
top
Crystal data top
K2Ca2Mg(SO4)4·2H2O | Z = 1 |
Mr = 602.92 | F(000) = 302 |
Triclinic, P1 | Dx = 2.763 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 6.975 (3) Å | Cell parameters from 1206 reflections |
b = 6.984 (3) Å | θ = 10.2–26.4° |
c = 8.899 (3) Å | µ = 2.09 mm−1 |
α = 104.01 (3)° | T = 298 K |
β = 101.19 (3)° | Prism, colourless |
γ = 114.10 (6)° | 0.35 × 0.33 × 0.32 mm |
V = 362.3 (4) Å3 | |
Data collection top
Oxford Diffraction Xcalibur-3 diffractometer | 1525 independent reflections |
Radiation source: fine-focus sealed tube | 1305 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.025 |
ω scans | θmax = 31.3°, θmin = 4.2° |
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997) | h = −9→6 |
Tmin = 0.493, Tmax = 0.510 | k = −7→10 |
2629 measured reflections | l = −10→12 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.048 | H-atom parameters not defined |
wR(F2) = 0.143 | w = 1/[σ2(Fo2) + (0.0856P)2 + 1.9844P] where P = (Fo2 + 2Fc2)/3 |
S = 0.97 | (Δ/σ)max < 0.001 |
1525 reflections | Δρmax = 1.19 e Å−3 |
124 parameters | Δρmin = −0.68 e Å−3 |
0 restraints | |
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 | |
S1 | 0.31293 (17) | 0.56434 (16) | 0.14152 (12) | 0.0125 (3) | |
S2 | −0.05661 (18) | 0.18567 (16) | 0.35769 (12) | 0.0131 (3) | |
Mg | 0.0000 | 0.0000 | 0.0000 | 0.0153 (5) | |
Ca | 0.12539 (14) | 0.36459 (14) | −0.25711 (10) | 0.0146 (3) | |
K | 0.52448 (17) | 0.78828 (17) | 0.57178 (12) | 0.0229 (3) | |
O1 | −0.0370 (5) | 0.0082 (5) | 0.2369 (4) | 0.0174 (7) | |
O2 | 0.1284 (6) | 0.3354 (5) | 0.0387 (4) | 0.0220 (7) | |
O3 | 0.4986 (5) | 0.5540 (5) | 0.2415 (4) | 0.0202 (7) | |
O4 | −0.2344 (5) | 0.3100 (5) | 0.7517 (4) | 0.0189 (7) | |
O5 | 0.3782 (6) | 0.6721 (5) | 0.0222 (4) | 0.0216 (7) | |
O6 | −0.1728 (5) | 0.2786 (5) | 0.2687 (4) | 0.0188 (7) | |
O7 | −0.1778 (6) | 0.0844 (5) | 0.4601 (4) | 0.0211 (7) | |
O8 | 0.1677 (5) | 0.3610 (5) | 0.4680 (4) | 0.0223 (7) | |
O9 | 0.3107 (5) | 0.0432 (5) | 0.0829 (4) | 0.0152 (6) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
S1 | 0.0121 (6) | 0.0127 (5) | 0.0125 (5) | 0.0065 (4) | 0.0044 (4) | 0.0028 (4) |
S2 | 0.0144 (6) | 0.0125 (5) | 0.0124 (4) | 0.0073 (4) | 0.0045 (4) | 0.0030 (4) |
Mg | 0.0140 (10) | 0.0152 (10) | 0.0138 (9) | 0.0065 (8) | 0.0030 (8) | 0.0028 (7) |
Ca | 0.0132 (5) | 0.0144 (5) | 0.0162 (4) | 0.0067 (4) | 0.0049 (3) | 0.0052 (3) |
K | 0.0199 (6) | 0.0244 (6) | 0.0227 (5) | 0.0100 (5) | 0.0070 (4) | 0.0067 (4) |
O1 | 0.0246 (17) | 0.0158 (15) | 0.0138 (13) | 0.0126 (13) | 0.0066 (12) | 0.0031 (11) |
O2 | 0.0187 (17) | 0.0153 (15) | 0.0239 (16) | 0.0065 (14) | 0.0019 (13) | 0.0007 (12) |
O3 | 0.0186 (17) | 0.0232 (16) | 0.0172 (15) | 0.0114 (14) | 0.0033 (13) | 0.0038 (12) |
O4 | 0.0172 (16) | 0.0203 (16) | 0.0156 (14) | 0.0086 (13) | 0.0057 (12) | 0.0010 (12) |
O5 | 0.0253 (18) | 0.0211 (16) | 0.0200 (15) | 0.0115 (15) | 0.0094 (13) | 0.0077 (13) |
O6 | 0.0213 (17) | 0.0190 (15) | 0.0186 (14) | 0.0129 (14) | 0.0045 (13) | 0.0065 (12) |
O7 | 0.0229 (18) | 0.0223 (16) | 0.0219 (15) | 0.0107 (14) | 0.0118 (14) | 0.0108 (13) |
O8 | 0.0168 (17) | 0.0198 (16) | 0.0191 (15) | 0.0052 (14) | 0.0003 (13) | −0.0002 (12) |
O9 | 0.0132 (15) | 0.0135 (15) | 0.0244 (15) | 0.0083 (13) | 0.0103 (13) | 0.0090 (12) |
Geometric parameters (Å, º) top
S1—O3 | 1.461 (3) | Ca—S2vi | 3.141 (2) |
S1—O4i | 1.471 (3) | Ca—Kvi | 3.990 (3) |
S1—O5 | 1.482 (3) | K—O8 | 2.768 (4) |
S1—O2 | 1.484 (4) | K—O8iii | 2.787 (4) |
S1—Ca | 3.249 (2) | K—O7ix | 2.804 (4) |
S1—K | 3.508 (2) | K—O9iii | 2.815 (4) |
S2—O6 | 1.461 (3) | K—O7i | 2.886 (4) |
S2—O8 | 1.472 (4) | K—O4i | 2.916 (4) |
S2—O7 | 1.473 (3) | K—O3 | 2.928 (3) |
S2—O1 | 1.504 (3) | K—O6i | 2.998 (4) |
S2—Caii | 3.141 (2) | K—O4ix | 3.129 (4) |
S2—Ki | 3.507 (2) | K—O1iii | 3.164 (4) |
S2—Kiii | 3.563 (2) | K—O3iii | 3.196 (4) |
Mg—O9iv | 2.017 (3) | K—S2i | 3.507 (2) |
Mg—O9 | 2.017 (3) | O1—Caiv | 2.479 (3) |
Mg—O2 | 2.045 (3) | O1—Kiii | 3.164 (4) |
Mg—O2iv | 2.045 (3) | O3—Caviii | 2.413 (4) |
Mg—O1iv | 2.164 (3) | O3—Kiii | 3.196 (4) |
Mg—O1 | 2.164 (3) | O4—S1i | 1.471 (3) |
Mg—Ca | 3.7765 (17) | O4—Caii | 2.399 (3) |
Mg—Caiv | 3.7765 (17) | O4—Ki | 2.916 (4) |
Mg—Kv | 4.009 (3) | O4—Kx | 3.129 (4) |
Mg—Kiii | 4.009 (3) | O6—Cavii | 2.407 (3) |
Ca—O4vi | 2.399 (3) | O6—Ki | 2.998 (4) |
Ca—O6vii | 2.407 (3) | O7—Caii | 2.609 (4) |
Ca—O3viii | 2.413 (4) | O7—Kx | 2.804 (4) |
Ca—O1iv | 2.479 (3) | O7—Ki | 2.886 (4) |
Ca—O8vi | 2.516 (4) | O8—Caii | 2.516 (4) |
Ca—O5 | 2.554 (4) | O8—Kiii | 2.787 (4) |
Ca—O7vi | 2.609 (4) | O9—Kiii | 2.815 (4) |
Ca—O2 | 2.686 (4) | | |
| | | |
O3—S1—O4i | 109.71 (18) | O7i—K—O3 | 107.94 (10) |
O3—S1—O5 | 111.3 (2) | O4i—K—O3 | 48.44 (9) |
O4i—S1—O5 | 109.75 (19) | O8—K—O6i | 62.04 (10) |
O3—S1—O2 | 111.0 (2) | O8iii—K—O6i | 139.56 (10) |
O4i—S1—O2 | 110.41 (19) | O7ix—K—O6i | 144.82 (10) |
O5—S1—O2 | 104.6 (2) | O9iii—K—O6i | 65.64 (10) |
O6—S2—O8 | 111.4 (2) | O7i—K—O6i | 48.48 (9) |
O6—S2—O7 | 111.0 (2) | O4i—K—O6i | 95.12 (10) |
O8—S2—O7 | 107.1 (2) | O3—K—O6i | 130.99 (10) |
O6—S2—O1 | 109.36 (18) | O8—K—O4ix | 153.33 (10) |
O8—S2—O1 | 109.03 (19) | O8iii—K—O4ix | 110.59 (11) |
O7—S2—O1 | 108.91 (19) | O7ix—K—O4ix | 57.78 (10) |
O9iv—Mg—O9 | 180.0 (2) | O9iii—K—O4ix | 62.28 (9) |
O9iv—Mg—O2 | 90.04 (14) | O7i—K—O4ix | 74.23 (11) |
O9—Mg—O2 | 89.96 (14) | O4i—K—O4ix | 106.94 (9) |
O9iv—Mg—O2iv | 89.96 (14) | O3—K—O4ix | 125.63 (10) |
O9—Mg—O2iv | 90.04 (14) | O6i—K—O4ix | 92.18 (10) |
O2—Mg—O2iv | 180.00 (8) | O8—K—O1iii | 132.35 (11) |
O9iv—Mg—O1iv | 90.24 (13) | O8iii—K—O1iii | 47.53 (9) |
O9—Mg—O1iv | 89.76 (13) | O7ix—K—O1iii | 63.64 (10) |
O2—Mg—O1iv | 80.97 (13) | O9iii—K—O1iii | 59.10 (9) |
O2iv—Mg—O1iv | 99.03 (13) | O7i—K—O1iii | 140.33 (10) |
O9iv—Mg—O1 | 89.76 (13) | O4i—K—O1iii | 139.29 (9) |
O9—Mg—O1 | 90.24 (13) | O3—K—O1iii | 100.55 (10) |
O2—Mg—O1 | 99.03 (13) | O6i—K—O1iii | 124.55 (9) |
O2iv—Mg—O1 | 80.97 (13) | O4ix—K—O1iii | 66.78 (10) |
O1iv—Mg—O1 | 180.0 (3) | O8—K—O3iii | 57.04 (10) |
O4vi—Ca—O6vii | 83.00 (13) | O8iii—K—O3iii | 69.66 (10) |
O4vi—Ca—O3viii | 174.75 (10) | O7ix—K—O3iii | 140.08 (10) |
O6vii—Ca—O3viii | 94.95 (13) | O9iii—K—O3iii | 61.17 (9) |
O4vi—Ca—O1iv | 90.45 (13) | O7i—K—O3iii | 117.51 (10) |
O6vii—Ca—O1iv | 173.31 (11) | O4i—K—O3iii | 127.44 (11) |
O3viii—Ca—O1iv | 91.47 (13) | O3—K—O3iii | 104.25 (9) |
O4vi—Ca—O8vi | 112.64 (12) | O6i—K—O3iii | 69.91 (9) |
O6vii—Ca—O8vi | 74.40 (11) | O4ix—K—O3iii | 123.14 (9) |
O3viii—Ca—O8vi | 71.24 (11) | O1iii—K—O3iii | 80.03 (10) |
O1iv—Ca—O8vi | 109.59 (11) | S2—O1—Mg | 127.23 (18) |
O4vi—Ca—O5 | 101.30 (12) | S2—O1—Caiv | 122.93 (17) |
O6vii—Ca—O5 | 70.77 (11) | Mg—O1—Caiv | 108.66 (12) |
O3viii—Ca—O5 | 73.45 (12) | S2—O1—Kiii | 92.51 (15) |
O1iv—Ca—O5 | 109.45 (12) | Mg—O1—Kiii | 95.77 (12) |
O8vi—Ca—O5 | 127.08 (12) | Caiv—O1—Kiii | 92.57 (12) |
O4vi—Ca—O7vi | 70.09 (11) | S1—O2—Mg | 145.4 (2) |
O6vii—Ca—O7vi | 102.05 (12) | S1—O2—Ca | 98.19 (17) |
O3viii—Ca—O7vi | 115.12 (11) | Mg—O2—Ca | 105.10 (13) |
O1iv—Ca—O7vi | 76.80 (12) | S1—O3—Caviii | 138.7 (2) |
O8vi—Ca—O7vi | 55.02 (11) | S1—O3—K | 100.78 (15) |
O5—Ca—O7vi | 169.78 (11) | Caviii—O3—K | 105.95 (12) |
O4vi—Ca—O2 | 76.04 (11) | S1—O3—Kiii | 127.72 (19) |
O6vii—Ca—O2 | 113.02 (11) | Caviii—O3—Kiii | 89.58 (11) |
O3viii—Ca—O2 | 100.46 (11) | K—O3—Kiii | 75.75 (9) |
O1iv—Ca—O2 | 63.77 (10) | S1i—O4—Caii | 134.43 (19) |
O8vi—Ca—O2 | 169.77 (11) | S1i—O4—Ki | 101.03 (16) |
O5—Ca—O2 | 53.15 (11) | Caii—O4—Ki | 110.68 (12) |
O7vi—Ca—O2 | 127.00 (11) | S1i—O4—Kx | 125.78 (17) |
O8—K—O8iii | 94.64 (11) | Caii—O4—Kx | 95.02 (12) |
O8—K—O7ix | 142.43 (11) | Ki—O4—Kx | 73.06 (9) |
O8iii—K—O7ix | 73.59 (11) | S1—O5—Ca | 104.04 (17) |
O8—K—O9iii | 108.26 (11) | S2—O6—Cavii | 140.1 (2) |
O8iii—K—O9iii | 95.22 (10) | S2—O6—Ki | 97.74 (16) |
O7ix—K—O9iii | 108.27 (11) | Cavii—O6—Ki | 94.55 (11) |
O8—K—O7i | 82.76 (11) | S2—O7—Caii | 96.67 (17) |
O8iii—K—O7i | 168.11 (10) | S2—O7—Kx | 163.9 (2) |
O7ix—K—O7i | 101.46 (10) | Caii—O7—Kx | 98.62 (12) |
O9iii—K—O7i | 96.61 (10) | S2—O7—Ki | 102.25 (17) |
O8—K—O4i | 71.25 (11) | Caii—O7—Ki | 105.67 (11) |
O8iii—K—O4i | 108.62 (10) | Kx—O7—Ki | 78.54 (10) |
O7ix—K—O4i | 78.88 (11) | S2—O8—Caii | 100.65 (17) |
O9iii—K—O4i | 156.15 (9) | S2—O8—K | 151.1 (2) |
O7i—K—O4i | 59.54 (9) | Caii—O8—K | 97.98 (11) |
O8—K—O3 | 74.07 (11) | S2—O8—Kiii | 109.64 (16) |
O8iii—K—O3 | 60.27 (10) | Caii—O8—Kiii | 107.37 (13) |
O7ix—K—O3 | 69.10 (11) | K—O8—Kiii | 85.36 (11) |
O9iii—K—O3 | 155.38 (10) | Mg—O9—Kiii | 111.05 (12) |
Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, y, z+1; (iii) −x+1, −y+1, −z+1; (iv) −x, −y, −z; (v) x−1, y−1, z−1; (vi) x, y, z−1; (vii) −x, −y+1, −z; (viii) −x+1, −y+1, −z; (ix) x+1, y+1, z; (x) x−1, y−1, z. |