The crystal structures of Fe-bearing MgCO3 sp2- and sp3-carbonates at 98 GPa from single-crystal X-ray diffraction using synchrotron radiation

Chariton, S.; Bykov, M.; Bykova, E.; Koemets, E.; Fedotenko, T.; Winkler, B.; Hanfland, M.; Prakapenka, V.B.; Greenberg, E.; McCammon, C.; Dubrovinsky, L.

doi:10.1107/S2056989020005411

The crystal structures of Fe-bearing MgCO₃ sp²- and sp³-carbonates at 98 GPa from single-crystal X-ray diffraction using synchrotron radiation

S. Chariton, M. Bykov, E. Bykova, E. Koemets, T. Fedotenko, B. Winkler, M. Hanfland, V. B. Prakapenka, E. Greenberg, C. McCammon and L. Dubrovinsky

We report the phase transition of Mg_0.85Fe_0.15CO₃ sp²- to Mg_2.53Fe_0.47C₃O₉ sp³-carbonate (MgCO₃–II phase) at 98 GPa and describe their crystal structures by means of single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells.

Keywords: carbonates; magnesite-II; sp³-carbonates; sp²-carbonates; crystal structure; high-pressure single-crystal X-ray diffraction.

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Supporting information

Crystallographic Information File (CIF) https://doi.org/10.1107/S2056989020005411/wm5543sup1.cif
Contains datablocks MgCO3-II_98GPa, MgCO3_98GPa

CCDC references: 1998018; 1998019

checkCIF report

Key indicators

Single-crystal synchrotron study
T = 293 K, P = 0.0 kPa
Mean (O-C) = 0.021 Å
Mean (O-C) = 0.008 Å
Disorder in main residue
R factor = 0.084
wR factor = 0.095
Data-to-parameter ratio = 7.6

checkCIF/PLATON results

No syntax errors found



Datablock: MgCO3-II_98GPa



Alert level A
ATOM007_ALERT_1_A  _atom_site_aniso_label is missing
            Unique label identifying the atom site.

Author Response: Due to the limited number of available reflections the structure was refined isotropically.

PLAT029_ALERT_3_A _diffrn_measured_fraction_theta_full value Low .      0.510 Why?
              Mg1     Mg2     Mg3     O1      O2      O3                  etc.

Author Response: This measurement was performed inside a diamond anvil cell at high pressure. This alert is common and expected for experiments performed in diamond anvil cells.


Alert level B
PLAT088_ALERT_3_B Poor Data / Parameter Ratio ....................       7.64 Note

Author Response: This measurement was performed inside a diamond anvil cell at high pressure. At such experimental conditions the number of available unique reflections is typically very limited, thus unavoidably resulting in low data/parameter ratios.

PLAT149_ALERT_3_B s.u. on the   beta    Angle is Too Large .......       0.06 Degree

Author Response: The low fraction of reflection data available in our diamond-anvil-cell-measurement leads to low precision.


Alert level C
GOODF01_ALERT_2_C  The least squares goodness of fit parameter lies
            outside the range 0.80 <> 2.00
            Goodness of fit given =      3.210
PLAT041_ALERT_1_C Calc. and Reported SumFormula    Strings  Differ     Please Check
PLAT043_ALERT_1_C Calculated and Reported Mol. Weight Differ by ..       9.11 Check
PLAT077_ALERT_4_C Unitcell Contains Non-integer Number of Atoms ..     Please Check
PLAT971_ALERT_2_C Check Calcd Resid. Dens.  0.61A   From Fe3             1.83 eA-3
PLAT992_ALERT_5_C Repd & Actual _reflns_number_gt Values Differ by         15 Check

Alert level G
ABSMU01_ALERT_1_G  Calculation of _exptl_absorpt_correction_mu
                not performed for this radiation type.
PLAT004_ALERT_5_G Polymeric Structure Found with Maximum Dimension          3 Info
PLAT005_ALERT_5_G No Embedded Refinement Details Found  in the CIF     Please Do !
PLAT040_ALERT_1_G No H-atoms in this Carbon Containing Compound ..     Please Check
PLAT042_ALERT_1_G Calc. and Reported MoietyFormula Strings  Differ     Please Check
PLAT045_ALERT_1_G Calculated and Reported Z Differ by a Factor ...       0.25 Check
PLAT092_ALERT_4_G Check: Wavelength Given is not Cu,Ga,Mo,Ag,In Ka    0.41107 Ang.
PLAT199_ALERT_1_G Reported _cell_measurement_temperature ..... (K)        293 Check
PLAT200_ALERT_1_G Reported   _diffrn_ambient_temperature ..... (K)        293 Check
PLAT301_ALERT_3_G Main Residue  Disorder ..............(Resd  1  )        22% Note
PLAT432_ALERT_2_G Short Inter X...Y Contact  O3       ..C1               2.73 Ang.
                                                  -x,-y,1-z  =      3_556 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  O5       ..C1               2.82 Ang.
                                                  -x,-y,1-z  =      3_556 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  O6       ..C2               2.62 Ang.
                                            1/2-x,1/2+y,2-z  =      6_557 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  C1       ..C2               3.20 Ang.
                                            1/2-x,1/2+y,2-z  =      6_557 Check
PLAT808_ALERT_5_G No Parseable SHELXL Style Weighting Scheme Found     Please Check
PLAT883_ALERT_1_G No Info/Value for _atom_sites_solution_primary .     Please Do !
PLAT910_ALERT_3_G Missing # of FCF Reflection(s) Below Theta(Min).          1 Note
PLAT911_ALERT_3_G Missing FCF Refl Between Thmin & STh/L=    0.600        181 Report
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600        393 Note
PLAT929_ALERT_5_G No Weight Pars,Obs and Calc R1,wR2,S not Checked          ! Info
PLAT950_ALERT_5_G Calculated (ThMax) and CIF-Reported Hmax Differ           2 Units
PLAT951_ALERT_5_G Calculated (ThMax) and CIF-Reported Kmax Differ           3 Units
PLAT952_ALERT_5_G Calculated (ThMax) and CIF-Reported Lmax Differ           2 Units
PLAT956_ALERT_1_G Calculated (ThMax) and Actual (FCF) Hmax Differ           2 Units
PLAT957_ALERT_1_G Calculated (ThMax) and Actual (FCF) Kmax Differ           3 Units
PLAT958_ALERT_1_G Calculated (ThMax) and Actual (FCF) Lmax Differ           2 Units
PLAT960_ALERT_3_G Number of Intensities with I  <   - 2*sig(I) ...          1 Check
PLAT985_ALERT_1_G The Fe-f"=    0.3056 Deviates from the B&C-Value     0.3033 Check

   2 ALERT level A = Most likely a serious problem - resolve or explain
   2 ALERT level B = A potentially serious problem, consider carefully
   6 ALERT level C = Check. Ensure it is not caused by an omission or oversight
  28 ALERT level G = General information/check it is not something unexpected

  14 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   6 ALERT type 2 Indicator that the structure model may be wrong or deficient
   7 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   8 ALERT type 5 Informative message, check




Datablock: MgCO3_98GPa



Alert level A
ATOM007_ALERT_1_A  _atom_site_aniso_label is missing
            Unique label identifying the atom site.

Author Response: Due to the limited number of available reflections the structure was refined isotropically.

PLAT029_ALERT_3_A _diffrn_measured_fraction_theta_full value Low .      0.920 Why?

Author Response: This measurement was performed inside a diamond anvil cell at high pressure. This alert is common and expected for experiments performed in diamond anvil cells.


Alert level C
GOODF01_ALERT_2_C  The least squares goodness of fit parameter lies
            outside the range 0.80 <> 2.00
            Goodness of fit given =      2.890
PLAT041_ALERT_1_C Calc. and Reported SumFormula    Strings  Differ     Please Check
PLAT077_ALERT_4_C Unitcell Contains Non-integer Number of Atoms ..     Please Check
PLAT148_ALERT_3_C s.u. on the      a    - Axis is (Too) Large ....      0.007 Ang.
PLAT148_ALERT_3_C s.u. on the      c    - Axis is (Too) Large ....      0.020 Ang.

Alert level G
ABSMU01_ALERT_1_G  Calculation of _exptl_absorpt_correction_mu
                not performed for this radiation type.
PLAT004_ALERT_5_G Polymeric Structure Found with Maximum Dimension          2 Info
PLAT005_ALERT_5_G No Embedded Refinement Details Found  in the CIF     Please Do !
PLAT040_ALERT_1_G No H-atoms in this Carbon Containing Compound ..     Please Check
PLAT045_ALERT_1_G Calculated and Reported Z Differ by a Factor ...       0.17 Check
PLAT092_ALERT_4_G Check: Wavelength Given is not Cu,Ga,Mo,Ag,In Ka    0.29520 Ang.
PLAT152_ALERT_1_G The Supplied and Calc. Volume s.u. Differ by ...          3 Units
PLAT199_ALERT_1_G Reported _cell_measurement_temperature ..... (K)        293 Check
PLAT200_ALERT_1_G Reported   _diffrn_ambient_temperature ..... (K)        293 Check
PLAT300_ALERT_4_G Atom Site Occupancy of Fe1        Constrained at       0.15 Check
PLAT300_ALERT_4_G Atom Site Occupancy of Mg1        Constrained at       0.85 Check
PLAT301_ALERT_3_G Main Residue  Disorder ..............(Resd  1  )        49% Note
PLAT432_ALERT_2_G Short Inter X...Y Contact  O1       ..C1               2.55 Ang.
                                         1/3-y,-1/3-x,1/6+z  =     34_545 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  C1       ..C1               3.19 Ang.
                                       1/3+x-y,-2/3+x,1/3-z  =     21_445 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  C1       ..C1               3.19 Ang.
                                       -1/3+y,1/3-x+y,1/3-z  =     20_455 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  C1       ..C1               3.19 Ang.
                                          1/3-x,2/3-y,2/3-z  =     31_555 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  C1       ..C1               3.19 Ang.
                                        -2/3-x,-1/3-y,2/3-z  =     31_445 Check
PLAT432_ALERT_2_G Short Inter X...Y Contact  C1       ..C1               3.19 Ang.
                                         1/3-y,-1/3-x,1/6+z  =     34_545 Check
PLAT808_ALERT_5_G No Parseable SHELXL Style Weighting Scheme Found     Please Check
PLAT811_ALERT_5_G No ADDSYM Analysis: Too Many Excluded Atoms ....          ! Info
PLAT883_ALERT_1_G No Info/Value for _atom_sites_solution_primary .     Please Do !
PLAT910_ALERT_3_G Missing # of FCF Reflection(s) Below Theta(Min).          4 Note
PLAT911_ALERT_3_G Missing FCF Refl Between Thmin & STh/L=    0.600         17 Report
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         51 Note
PLAT913_ALERT_3_G Missing # of Very Strong Reflections in FCF ....          1 Note
PLAT929_ALERT_5_G No Weight Pars,Obs and Calc R1,wR2,S not Checked          ! Info
PLAT952_ALERT_5_G Calculated (ThMax) and CIF-Reported Lmax Differ           3 Units
PLAT958_ALERT_1_G Calculated (ThMax) and Actual (FCF) Lmax Differ           3 Units
PLAT992_ALERT_5_G Repd & Actual _reflns_number_gt Values Differ by          5 Check

   2 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   5 ALERT level C = Check. Ensure it is not caused by an omission or oversight
  29 ALERT level G = General information/check it is not something unexpected

  10 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   7 ALERT type 2 Indicator that the structure model may be wrong or deficient
   7 ALERT type 3 Indicator that the structure quality may be low
   5 ALERT type 4 Improvement, methodology, query or suggestion
   7 ALERT type 5 Informative message, check


checkCIF publication errors

Alert level A
PUBL024_ALERT_1_A The number of authors is greater than 9.
              Please specify the role of each of the co-authors
              for your paper.

Author Response: The study was designed by SC, LD and CM. The starting material was synthesized and charachterized by SC. The diamond anvil cell was prepared by SC and LD. The beamline experimental set-ups were prepared by MH, VBP and EG. BW performed the DFT-based model calculations. The diffraction experiments were performed by SC, BM, EK and TF and the data were analyzed by SC and EB. SC, LD and CM discussed the results and wrote the manuscript with contributions from all authors.


   1 ALERT level A = Data missing that is essential or data in wrong format
   0 ALERT level G = General alerts. Data that may be required is missing

Computing details top

For both structures, data collection: CrysAlis PRO (Rigaku OD, 2019); cell refinement: CrysAlis PRO (Rigaku OD, 2019); data reduction: CrysAlis PRO (Rigaku OD, 2019); program(s) used to solve structure: Superflip (Palatinus & Chapuis, 2007); program(s) used to refine structure: Jana2006 (Petříček et al., 2014); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).

Magnesium(II) iron(II) carbonate (MgCO3-II_98GPa) top

Crystal data top

3[(Mg_0.85Fe_0.15)CO₃]	F(000) = 530
M_r = 265.6	D_x = 4.861 Mg m⁻³
Monoclinic, C2/m	Synchrotron radiation, λ = 0.41107 Å
Hall symbol: -C 2y	Cell parameters from 146 reflections
a = 8.238 (3) Å	θ = 2.3–19.0°
b = 6.5774 (12) Å	µ = 0.58 mm⁻¹
c = 6.974 (5) Å	T = 293 K
β = 104.40 (6)°	Irregular, colourless
V = 366.0 (3) Å³	0.01 × 0.01 × 0.01 mm
Z = 4

Data collection top

ID15b @ ESRF diffractometer	298 independent reflections
Radiation source: synchrotron	211 reflections with I > 3σ(I)
Synchrotron monochromator	R_int = 0.020
ω scans	θ_max = 20.7°, θ_min = 2.3°
Absorption correction: multi-scan (CrysAlisPro; Rigaku OD, 2019)	h = −11→12
T_min = 0.104, T_max = 1	k = −8→8
522 measured reflections	l = −7→9

Refinement top

Refinement on F	0 restraints
Least-squares matrix: full	5 constraints
R[F² > 2σ(F²)] = 0.084	Weighting scheme based on measured s.u.'s w = 1/(σ²(F) + 0.000144F²)
wR(F²) = 0.095	(Δ/σ)_max = 0.001
S = 3.21	Δρ_max = 1.76 e Å⁻³
298 reflections	Δρ_min = −1.21 e Å⁻³
39 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Mg3	0.4441 (6)	0	0.6503 (9)	0.0177 (11)*	0.61 (2)
Fe3	0.4441 (6)	0	0.6503 (9)	0.0177 (11)*	0.39 (2)
Mg2	0.1712 (7)	0	0.3146 (12)	0.0086 (11)*
Mg1	0	0.2457 (6)	0	0.0117 (13)*	0.917 (17)
Fe1	0	0.2457 (6)	0	0.0117 (13)*	0.083 (17)
O4	0.1395 (17)	0	0.044 (3)	0.020 (2)*
O6	0.2736 (13)	0.1662 (9)	0.847 (2)	0.0179 (17)*
O2	0.3442 (12)	0.1683 (9)	0.4218 (18)	0.0157 (15)*
O1	0.4097 (18)	0	0.105 (3)	0.021 (2)*
O5	0.1487 (16)	0	0.575 (3)	0.016 (2)*
O3	0.0062 (12)	0.1898 (9)	0.2702 (19)	0.0159 (17)*
C1	0.1347 (19)	0.1774 (13)	0.683 (3)	0.017 (2)*
C2	0.265 (3)	0	0.964 (4)	0.024 (3)*

Geometric parameters (Å, º) top

Mg3—O6	2.451 (14)	Mg2—O3ⁱ	1.814 (9)
Mg3—O6ⁱ	2.451 (14)	Mg1—O4	1.962 (8)
Mg3—O2	1.947 (11)	Mg1—O4^vi	1.962 (8)
Mg3—O2ⁱⁱ	2.226 (11)	Mg1—O6^v	1.991 (10)
Mg3—O2ⁱⁱⁱ	2.226 (11)	Mg1—O6^vii	1.991 (10)
Mg3—O2ⁱ	1.947 (11)	Mg1—O1^viii	2.039 (12)
Mg3—O1ⁱⁱ	1.829 (18)	Mg1—O1^ix	2.039 (12)
Mg3—O5	2.359 (14)	Mg1—O3	1.908 (13)
Mg3—O3^iv	2.127 (7)	Mg1—O3^vi	1.908 (13)
Mg3—O3^v	2.127 (7)	Fe1—O4	1.962 (8)
Fe3—O6	2.451 (14)	Fe1—O4^vi	1.962 (8)
Fe3—O6ⁱ	2.451 (14)	Fe1—O6^v	1.991 (10)
Fe3—O2	1.947 (11)	Fe1—O6^vii	1.991 (10)
Fe3—O2ⁱⁱ	2.226 (11)	Fe1—O1^viii	2.039 (12)
Fe3—O2ⁱⁱⁱ	2.226 (11)	Fe1—O1^ix	2.039 (12)
Fe3—O2ⁱ	1.947 (11)	Fe1—O3	1.908 (13)
Fe3—O1ⁱⁱ	1.829 (18)	Fe1—O3^vi	1.908 (13)
Fe3—O5	2.359 (14)	C1—O6	1.403 (19)
Fe3—O3^iv	2.127 (7)	C1—O2^v	1.288 (18)
Fe3—O3^v	2.127 (7)	C1—O5	1.411 (17)
Mg2—O4	1.84 (2)	C1—O3^x	1.28 (2)
Mg2—O2	1.813 (9)	C2—O4^xi	1.29 (3)
Mg2—O2ⁱ	1.813 (9)	C2—O6	1.38 (2)
Mg2—O5	1.87 (2)	C2—O6ⁱ	1.38 (2)
Mg2—O3	1.814 (9)	C2—O1^xi	1.34 (3)

O6—Mg3—O6ⁱ	53.0 (3)	O5—Fe3—O3^iv	100.3 (3)
O6—Mg3—O2	91.1 (4)	O5—Fe3—O3^v	100.3 (3)
O6—Mg3—O2ⁱⁱ	119.7 (3)	O3^iv—Fe3—O3^v	147.1 (5)
O6—Mg3—O2ⁱⁱⁱ	159.8 (5)	O4—Mg2—O2	108.6 (6)
O6—Mg3—O2ⁱ	121.8 (4)	O4—Mg2—O2ⁱ	108.6 (6)
O6—Mg3—O1ⁱⁱ	79.3 (6)	O4—Mg2—O5	166.6 (7)
O6—Mg3—O5	54.7 (5)	O4—Mg2—O3	85.1 (6)
O6—Mg3—O3^iv	112.4 (5)	O4—Mg2—O3ⁱ	85.1 (6)
O6—Mg3—O3^v	61.7 (4)	O2—Mg2—O2ⁱ	75.3 (4)
O6ⁱ—Mg3—O2	121.8 (4)	O2—Mg2—O5	81.8 (6)
O6ⁱ—Mg3—O2ⁱⁱ	159.8 (5)	O2—Mg2—O3	97.4 (4)
O6ⁱ—Mg3—O2ⁱⁱⁱ	119.7 (3)	O2—Mg2—O3ⁱ	165.8 (7)
O6ⁱ—Mg3—O2ⁱ	91.1 (4)	O2ⁱ—Mg2—O5	81.8 (6)
O6ⁱ—Mg3—O1ⁱⁱ	79.3 (6)	O2ⁱ—Mg2—O3	165.8 (7)
O6ⁱ—Mg3—O5	54.7 (5)	O2ⁱ—Mg2—O3ⁱ	97.4 (4)
O6ⁱ—Mg3—O3^iv	61.7 (4)	O5—Mg2—O3	85.1 (6)
O6ⁱ—Mg3—O3^v	112.4 (5)	O5—Mg2—O3ⁱ	85.1 (6)
O2—Mg3—O2ⁱⁱ	74.2 (4)	O3—Mg2—O3ⁱ	87.0 (4)
O2—Mg3—O2ⁱⁱⁱ	107.0 (5)	O4—Mg1—O4^vi	69.1 (5)
O2—Mg3—O2ⁱ	69.3 (4)	O4—Mg1—O6^v	73.9 (4)
O2—Mg3—O1ⁱⁱ	144.2 (3)	O4—Mg1—O6^vii	139.3 (4)
O2—Mg3—O5	67.3 (5)	O4—Mg1—O1^viii	150.6 (7)
O2—Mg3—O3^iv	140.7 (5)	O4—Mg1—O1^ix	118.7 (6)
O2—Mg3—O3^v	71.5 (4)	O4—Mg1—O3	79.4 (6)
O2ⁱⁱ—Mg3—O2ⁱⁱⁱ	59.6 (3)	O4—Mg1—O3^vi	82.3 (6)
O2ⁱⁱ—Mg3—O2ⁱ	107.0 (5)	O4^vi—Mg1—O6^v	139.3 (4)
O2ⁱⁱ—Mg3—O1ⁱⁱ	80.8 (6)	O4^vi—Mg1—O6^vii	73.9 (4)
O2ⁱⁱ—Mg3—O5	140.5 (4)	O4^vi—Mg1—O1^viii	118.7 (6)
O2ⁱⁱ—Mg3—O3^iv	115.2 (4)	O4^vi—Mg1—O1^ix	150.6 (7)
O2ⁱⁱ—Mg3—O3^v	58.1 (4)	O4^vi—Mg1—O3	82.3 (6)
O2ⁱⁱⁱ—Mg3—O2ⁱ	74.2 (4)	O4^vi—Mg1—O3^vi	79.4 (6)
O2ⁱⁱⁱ—Mg3—O1ⁱⁱ	80.8 (6)	O6^v—Mg1—O6^vii	146.1 (3)
O2ⁱⁱⁱ—Mg3—O5	140.5 (4)	O6^v—Mg1—O1^viii	86.9 (5)
O2ⁱⁱⁱ—Mg3—O3^iv	58.1 (4)	O6^v—Mg1—O1^ix	64.9 (5)
O2ⁱⁱⁱ—Mg3—O3^v	115.2 (4)	O6^v—Mg1—O3	74.6 (5)
O2ⁱ—Mg3—O1ⁱⁱ	144.2 (3)	O6^v—Mg1—O3^vi	112.2 (5)
O2ⁱ—Mg3—O5	67.3 (5)	O6^vii—Mg1—O1^viii	64.9 (5)
O2ⁱ—Mg3—O3^iv	71.5 (4)	O6^vii—Mg1—O1^ix	86.9 (5)
O2ⁱ—Mg3—O3^v	140.7 (5)	O6^vii—Mg1—O3	112.2 (5)
O1ⁱⁱ—Mg3—O5	127.7 (8)	O6^vii—Mg1—O3^vi	74.6 (5)
O1ⁱⁱ—Mg3—O3^iv	73.6 (3)	O1^viii—Mg1—O1^ix	69.7 (7)
O1ⁱⁱ—Mg3—O3^v	73.6 (3)	O1^viii—Mg1—O3	74.1 (6)
O5—Mg3—O3^iv	100.3 (3)	O1^viii—Mg1—O3^vi	126.1 (6)
O5—Mg3—O3^v	100.3 (3)	O1^ix—Mg1—O3	126.1 (6)
O3^iv—Mg3—O3^v	147.1 (5)	O1^ix—Mg1—O3^vi	74.1 (6)
O6—Fe3—O6ⁱ	53.0 (3)	O3—Mg1—O3^vi	157.8 (4)
O6—Fe3—O2	91.1 (4)	O4—Fe1—O4^vi	69.1 (5)
O6—Fe3—O2ⁱⁱ	119.7 (3)	O4—Fe1—O6^v	73.9 (4)
O6—Fe3—O2ⁱⁱⁱ	159.8 (5)	O4—Fe1—O6^vii	139.3 (4)
O6—Fe3—O2ⁱ	121.8 (4)	O4—Fe1—O1^viii	150.6 (7)
O6—Fe3—O1ⁱⁱ	79.3 (6)	O4—Fe1—O1^ix	118.7 (6)
O6—Fe3—O5	54.7 (5)	O4—Fe1—O3	79.4 (6)
O6—Fe3—O3^iv	112.4 (5)	O4—Fe1—O3^vi	82.3 (6)
O6—Fe3—O3^v	61.7 (4)	O4^vi—Fe1—O6^v	139.3 (4)
O6ⁱ—Fe3—O2	121.8 (4)	O4^vi—Fe1—O6^vii	73.9 (4)
O6ⁱ—Fe3—O2ⁱⁱ	159.8 (5)	O4^vi—Fe1—O1^viii	118.7 (6)
O6ⁱ—Fe3—O2ⁱⁱⁱ	119.7 (3)	O4^vi—Fe1—O1^ix	150.6 (7)
O6ⁱ—Fe3—O2ⁱ	91.1 (4)	O4^vi—Fe1—O3	82.3 (6)
O6ⁱ—Fe3—O1ⁱⁱ	79.3 (6)	O4^vi—Fe1—O3^vi	79.4 (6)
O6ⁱ—Fe3—O5	54.7 (5)	O6^v—Fe1—O6^vii	146.1 (3)
O6ⁱ—Fe3—O3^iv	61.7 (4)	O6^v—Fe1—O1^viii	86.9 (5)
O6ⁱ—Fe3—O3^v	112.4 (5)	O6^v—Fe1—O1^ix	64.9 (5)
O2—Fe3—O2ⁱⁱ	74.2 (4)	O6^v—Fe1—O3	74.6 (5)
O2—Fe3—O2ⁱⁱⁱ	107.0 (5)	O6^v—Fe1—O3^vi	112.2 (5)
O2—Fe3—O2ⁱ	69.3 (4)	O6^vii—Fe1—O1^viii	64.9 (5)
O2—Fe3—O1ⁱⁱ	144.2 (3)	O6^vii—Fe1—O1^ix	86.9 (5)
O2—Fe3—O5	67.3 (5)	O6^vii—Fe1—O3	112.2 (5)
O2—Fe3—O3^iv	140.7 (5)	O6^vii—Fe1—O3^vi	74.6 (5)
O2—Fe3—O3^v	71.5 (4)	O1^viii—Fe1—O1^ix	69.7 (7)
O2ⁱⁱ—Fe3—O2ⁱⁱⁱ	59.6 (3)	O1^viii—Fe1—O3	74.1 (6)
O2ⁱⁱ—Fe3—O2ⁱ	107.0 (5)	O1^viii—Fe1—O3^vi	126.1 (6)
O2ⁱⁱ—Fe3—O1ⁱⁱ	80.8 (6)	O1^ix—Fe1—O3	126.1 (6)
O2ⁱⁱ—Fe3—O5	140.5 (4)	O1^ix—Fe1—O3^vi	74.1 (6)
O2ⁱⁱ—Fe3—O3^iv	115.2 (4)	O3—Fe1—O3^vi	157.8 (4)
O2ⁱⁱ—Fe3—O3^v	58.1 (4)	O6—C1—O2^v	107.8 (11)
O2ⁱⁱⁱ—Fe3—O2ⁱ	74.2 (4)	O6—C1—O5	103.5 (10)
O2ⁱⁱⁱ—Fe3—O1ⁱⁱ	80.8 (6)	O6—C1—O3^x	113.7 (17)
O2ⁱⁱⁱ—Fe3—O5	140.5 (4)	O2^v—C1—O5	107.9 (17)
O2ⁱⁱⁱ—Fe3—O3^iv	58.1 (4)	O2^v—C1—O3^x	110.6 (10)
O2ⁱⁱⁱ—Fe3—O3^v	115.2 (4)	O5—C1—O3^x	112.8 (11)
O2ⁱ—Fe3—O1ⁱⁱ	144.2 (3)	O4^xi—C2—O6	114.7 (12)
O2ⁱ—Fe3—O5	67.3 (5)	O4^xi—C2—O6ⁱ	114.7 (12)
O2ⁱ—Fe3—O3^iv	71.5 (4)	O4^xi—C2—O1^xi	110 (3)
O2ⁱ—Fe3—O3^v	140.7 (5)	O6—C2—O6ⁱ	105 (2)
O1ⁱⁱ—Fe3—O5	127.7 (8)	O6—C2—O1^xi	105.7 (13)
O1ⁱⁱ—Fe3—O3^iv	73.6 (3)	O6ⁱ—C2—O1^xi	105.7 (13)
O1ⁱⁱ—Fe3—O3^v	73.6 (3)

Symmetry codes: (i) x, −y, z; (ii) −x+1, y, −z+1; (iii) −x+1, −y, −z+1; (iv) −x+1/2, y−1/2, −z+1; (v) −x+1/2, −y+1/2, −z+1; (vi) −x, y, −z; (vii) x−1/2, −y+1/2, z−1; (viii) x−1/2, y+1/2, z; (ix) −x+1/2, y+1/2, −z; (x) −x, y, −z+1; (xi) x, y, z+1.

Iron (II) Magnesium (II) carbonate (MgCO3_98GPa) top

Crystal data top

Mg_0.85Fe_0.15CO₃	D_x = 4.614 Mg m⁻³
M_r = 89	Synchrotron radiation, λ = 0.2952 Å
Trigonal, R3c	Cell parameters from 65 reflections
Hall symbol: -R 3 2"c	θ = 2.7–13.9°
a = 4.281 (7) Å	µ = 0.25 mm⁻¹
c = 12.12 (2) Å	T = 293 K
V = 192.3 (5) Å³	Irregular, colourless
Z = 6	0.01 × 0.01 × 0.01 mm
F(000) = 265

Data collection top

13IDD @ APS (GSECARS) diffractometer	60 independent reflections
Radiation source: synchrotron	33 reflections with I > 3σ(I)
Synchrotron monochromator	R_int = 0.053
ω scans	θ_max = 15.4°, θ_min = 2.7°
Absorption correction: multi-scan (CrysAlisPro; Rigaku OD, 2019)	h = −6→6
T_min = 0.95, T_max = 1	k = −7→5
176 measured reflections	l = −18→18

Refinement top

Refinement on F	0 restraints
Least-squares matrix: full	1 constraint
R[F² > 2σ(F²)] = 0.100	Weighting scheme based on measured s.u.'s w = 1/(σ²(F) + 0.000144F²)
wR(F²) = 0.084	(Δ/σ)_max < 0.001
S = 2.89	Δρ_max = 0.66 e Å⁻³
60 reflections	Δρ_min = −0.50 e Å⁻³
5 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Mg1	0	0	0	0.0373 (13)*	0.85
Fe1	0	0	0	0.0373 (13)*	0.15
O1	0.2791 (17)	0	0.25	0.0382 (16)*
C1	0	0	0.25	0.040 (3)*

Geometric parameters (Å, º) top

Mg1—O1ⁱ	1.855 (7)	Fe1—O1ⁱⁱⁱ	1.855 (8)
Mg1—O1ⁱⁱ	1.855 (5)	Fe1—O1^iv	1.855 (7)
Mg1—O1ⁱⁱⁱ	1.855 (8)	Fe1—O1^v	1.855 (5)
Mg1—O1^iv	1.855 (7)	Fe1—O1^vi	1.855 (8)
Mg1—O1^v	1.855 (5)	C1—O1	1.195 (8)
Mg1—O1^vi	1.855 (8)	C1—O1^vii	1.195 (8)
Fe1—O1ⁱ	1.855 (7)	C1—O1^viii	1.195 (8)
Fe1—O1ⁱⁱ	1.855 (5)

O1ⁱ—Mg1—O1ⁱⁱ	93.2 (2)	O1ⁱ—Fe1—O1^iv	180
O1ⁱ—Mg1—O1ⁱⁱⁱ	93.2 (2)	O1ⁱ—Fe1—O1^v	86.8 (2)
O1ⁱ—Mg1—O1^iv	180	O1ⁱ—Fe1—O1^vi	86.8 (2)
O1ⁱ—Mg1—O1^v	86.8 (2)	O1ⁱⁱ—Fe1—O1ⁱⁱⁱ	93.2 (3)
O1ⁱ—Mg1—O1^vi	86.8 (2)	O1ⁱⁱ—Fe1—O1^iv	86.8 (2)
O1ⁱⁱ—Mg1—O1ⁱⁱⁱ	93.2 (3)	O1ⁱⁱ—Fe1—O1^v	180
O1ⁱⁱ—Mg1—O1^iv	86.8 (2)	O1ⁱⁱ—Fe1—O1^vi	86.8 (3)
O1ⁱⁱ—Mg1—O1^v	180	O1ⁱⁱⁱ—Fe1—O1^iv	86.8 (2)
O1ⁱⁱ—Mg1—O1^vi	86.8 (3)	O1ⁱⁱⁱ—Fe1—O1^v	86.8 (3)
O1ⁱⁱⁱ—Mg1—O1^iv	86.8 (2)	O1ⁱⁱⁱ—Fe1—O1^vi	180
O1ⁱⁱⁱ—Mg1—O1^v	86.8 (3)	O1^iv—Fe1—O1^v	93.2 (2)
O1ⁱⁱⁱ—Mg1—O1^vi	180	O1^iv—Fe1—O1^vi	93.2 (2)
O1^iv—Mg1—O1^v	93.2 (2)	O1^v—Fe1—O1^vi	93.2 (3)
O1^iv—Mg1—O1^vi	93.2 (2)	O1—C1—O1^vii	120.00 (10)
O1^v—Mg1—O1^vi	93.2 (3)	O1—C1—O1^viii	120.0 (5)
O1ⁱ—Fe1—O1ⁱⁱ	93.2 (2)	O1^vii—C1—O1^viii	120.0 (5)
O1ⁱ—Fe1—O1ⁱⁱⁱ	93.2 (2)

Symmetry codes: (i) x−2/3, y−1/3, z−1/3; (ii) −y+1/3, x−y−1/3, z−1/3; (iii) −x+y+1/3, −x+2/3, z−1/3; (iv) −x+2/3, −y+1/3, −z+1/3; (v) y−1/3, −x+y+1/3, −z+1/3; (vi) x−y−1/3, x−2/3, −z+1/3; (vii) −y, x−y, z; (viii) −x+y, −x, z.

Geometric parameters of (Mg_2.53Fe_0.47)C₃O₉ at 98 GPa top

Group	Maximal bond length (Å)	Minimal bond length (Å)	Polyhedron volume (Å³)	Distortion index^a
CO₄ (C1—O)	1.409 (19)	1.287 (18)	1.25	0.045
CO₄ (C2—O)	1.38 (3)	1.29 (4)	1.25	0.022
M2O₆^b	1.87 (3)	1.813 (10)	7.78	0.010
M1O₈^c	2.039 (13)	1.908 (14)	13.24	0.020
M3O₈^d	2.358 (14)^e	1.828 (19)	14.59	0.068

Notes: (a) as defined in Baur (1974); (b) Mg:Fe ratio for M = 1:0; (c) Mg:Fe ratio for M = 0.917 (17):0.083 (17); (d) Mg:Fe ratio for M = 0.61 (2):0.39 (2); (e) alternatively, for CN = 10 the maximal distance is 2.451 (14) Å, the polyhedral volume is 20.58 Å³ and the distortion index is 0.080.

Fractional atomic coordinates and isotropic displacement parameters of (Mg_2.53Fe_0.47)C₃O₉ at 98 GPa. top

Atom label	x	y	z	Site symmetry	U_isco^[a]	Occupancy
Mg1	0	0.2457 (6)	0	4g	0.0117 (13)	0.917 (17)
Fe1	0	0.2457 (6)	0	4g	0.0117 (13)	0.083 (17)
Mg2	0.1712 (7)	0	0.3146 (12)	4i	0.0086 (11)	1
Mg3	0.4441 (6)	0	0.6503 (9)	4i	0.0177 (11)	0.61 (2)
Fe3	0.4441 (6)	0	0.6503 (9)	4i	0.0177 (11)	0.39 (2)
O1	0.4097 (18)	0	0.105 (3)	4i	0.021 (2)	1
O2	0.3442 (12)	0.1683 (9)	0.4218 (18)	8j	0.0157 (15)	1
O3	0.0062 (12)	0.1898 (9)	0.2702 (19)	8j	0.0159 (17)	1
O4	0.1395 (17)	0	0.044 (3)	4i	0.020 (2)	1
O5	0.1487 (16)	0	0.575 (3)	4i	0.016 (2)	1
O6	0.2736 (13)	0.1662 (9)	0.847 (2)	8j	0.0179 (17)	1
C1	0.1347 (19)	0.1774 (13)	0.683 (3)	8j	0.017 (2)	1
C2	0.265 (3)	0	0.964 (4)	4i	0.024 (3)	1

[a] All atomic displacement parameters were refined in the isotropic approximation

Fractional atomic coordinates and isotropic displacement parameters of (Mg_0.85Fe_0.15)CO₃ at 98 GPa. top

Atom label	x	y	z	Site symmetry	U_isco^[a]	Occupancy
Mg1	0	0	0	6b	0.0373 (13)	0.85
Fe1	0	0	0	6b	0.0373 (13)	0.15
O1	0.2791 (17)	0	0.25	18e	0.0382 (16)	1
C1	0	0	0.25	6a	0.04 (3)	1

[a] All atomic displacement parameters were refined in the isotropic approximation

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