Redetermination of despujolsite, Ca₃Mn⁴⁺(SO₄)₂(OH)₆·3H₂O

The crystal structure of despujolsite [tricalcium manganese bis­(sulfate) hexahydroxide tri­hydrate], the Ca/Mn member of the fleischerite group, ideally Ca₃Mn⁴⁺(SO₄)₂(OH)₆·3H₂O, was previously determined based on X-ray diffraction intensity data from photographs, without H-atom positions located [Gaudefroy et al. (1968). Bull. Soc. Fr. Minéral. Crystallogr. 91, 43-50]. The current study redetermines the structure of despujolsite from a natural specimen, with all H atoms located and with higher precision. The structure of despujolsite is characterized by layers of CaO₈ polyhedra (m.. symmetry) inter­connected by Mn(OH)₆ octa­hedra (32. symmetry) and SO₄ tetra­hedra (3.. symmetry) along [001]. The average Ca-O, Mn-O and S-O bond lengths are 2.489, 1.915, and 1.472 Å, respectively. There are two distinct hydrogen bonds that stabilize the structural set-up. This work represents the first description of hydrogen bonds in the fleischerite group of minerals.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Mn-O) = 0.006 Å
• R factor = 0.024
• wR factor = 0.048
• Data-to-parameter ratio = 17.8

checkCIF/PLATON results

No syntax errors found



Alert level A
PLAT113_ALERT_2_A ADDSYM Suggests Possible Pseudo/New Space-group.    P63/mmc

Author Response: Have checked and our space group is correct.

PLAT731_ALERT_1_A Bond    Calc    1.470(9), Rep  1.4697(11) ......          8 su-Ra
              S    -O2      1.555   3.565                    #         15

Author Response: Our data come directly from SHELX97, which is the most commonly used.

PLAT923_ALERT_1_A S    values in the CIF and FCF Differ by .......     -0.071

Author Response: a different weighting scheme definituion as used by SHELX and PLATON could be responsible for the difference

Alert level B
PLAT111_ALERT_2_B ADDSYM Detects (Pseudo) Centre of Symmetry .....        100 PerFi
PLAT112_ALERT_2_B ADDSYM Detects Additional (Pseudo) Symm. Elem...          6
PLAT112_ALERT_2_B ADDSYM Detects Additional (Pseudo) Symm. Elem...          m
PLAT112_ALERT_2_B ADDSYM Detects Additional (Pseudo) Symm. Elem...          m
PLAT112_ALERT_2_B ADDSYM Detects Additional (Pseudo) Symm. Elem...          m
PLAT731_ALERT_1_B Bond    Calc    1.915(7), Rep  1.9149(11) ......          6 su-Ra
              MN   -OH3     1.555   3.665                    #          1

Author Response: Our data come directly from SHELX97, which is the most commonly used.

PLAT731_ALERT_1_B Bond    Calc    1.915(7), Rep  1.9149(11) ......          6 su-Ra
              MN   -OH3     1.555   8.455                    #          2

Author Response: Our data come directly from SHELX97, which is the most commonly used.

PLAT731_ALERT_1_B Bond    Calc    1.915(6), Rep  1.9149(11) ......          6 su-Ra
              MN   -OH3     1.555   7.545                    #          5

Author Response: Our data come directly from SHELX97, which is the most commonly used.

PLAT731_ALERT_1_B Bond    Calc    1.915(7), Rep  1.9149(11) ......          6 su-Ra
              MN   -OH3     1.555   9.665                    #          6

Author Response: Our data come directly from SHELX97, which is the most commonly used.

PLAT731_ALERT_1_B Bond    Calc    1.470(5), Rep  1.4697(11) ......          5 su-Ra
              S    -O2      1.555   2.665                    #         16

Author Response: Our data come directly from SHELX97, which is the most commonly used.

PLAT737_ALERT_1_B D...A   Calc    2.819(8), Rep  2.8193(16) ......        5.0 su-Ra
              OH3  -O2      1.555   9.655                    #         18
PLAT737_ALERT_1_B D...A   Calc    2.789(9), Rep  2.7892(18) ......        5.0 su-Ra
              OW4  -O1      1.555   7.555                    #         18

Alert level C
STRVA01_ALERT_4_C           Flack test results are meaningless.
           From the CIF: _refine_ls_abs_structure_Flack    0.000
           From the CIF: _refine_ls_abs_structure_Flack_su    0.900
PLAT042_ALERT_1_C Calc. and Reported MoietyFormula Strings  Differ          ?
PLAT735_ALERT_1_C D-H     Calc     0.76(5), Rep     0.75(2) ......          3 su-Ra
              OH3  -H1      1.555   1.555                    #         18
PLAT735_ALERT_1_C D-H     Calc     0.77(5), Rep     0.77(2) ......          3 su-Ra
              OW4  -H2      1.555   1.555                    #         18
PLAT736_ALERT_1_C H...A   Calc     2.10(8), Rep     2.10(2) ......        4.0 su-Ra
              H2   -O1      1.555   7.555                    #         18
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          2
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600          4
PLAT922_ALERT_1_C wR2 in the CIF and FCF Differ by ...............     0.0038
PLAT927_ALERT_1_C Reported and Calculated  wR2 Differ by .........     0.0033

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           32.63
           From the CIF: _reflns_number_total                871
           Count of symmetry unique reflns          515
           Completeness (_total/calc)            169.13%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       356
           Fraction of Friedel pairs measured     0.691
           Are heavy atom types Z>Si present        yes
PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension .          1
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT032_ALERT_4_G Std. Uncertainty on Flack Parameter Value High .      0.900
PLAT152_ALERT_1_G The Supplied and Calc. Volume s.u. Differ by ...          3 Units
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          2
PLAT850_ALERT_4_G Check Flack Parameter Exact Value 0.00 and su ..       0.90
PLAT916_ALERT_2_G Hooft y and Flack x Parameter values differ by .       0.51

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

  18 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
   1 ALERT type 3 Indicator that the structure quality may be low
   6 ALERT type 4 Improvement, methodology, query or suggestion
   2 ALERT type 5 Informative message, check

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S1. Comment

Despujolsite, ideally Ca₃Mn⁴⁺(SO₄)₂(OH)₆^.3H₂O, is a member of the fleischerite group of minerals, which includes fleischerite, Pb₃Ge(SO₄)₂(OH)₆^.3H₂O, mallestigite, Pb₃Sb(SO₄)(AsO₄)(OH)₆^.3H₂O, and schauerteite, Ca₃Ge⁴⁺(SO₄)₂(OH)₆^.3H₂O. Thus far, only the structures of despujolsite and fleischerite (from a synthetic sample with the O1 site split) in this group have been determined (Gaudefroy et al., 1968; Otto, 1975), both of which were based on X-ray diffraction intensity data measured from photographs, without H atom positions located. An R-factor of 0.162 was obtained for the structure model of despujolsite (Gaudefroy et al., 1968). In our efforts to understand hydrogen bonding environments in general and the relationships in the hydrogen bonding schemes in the minerals of the fleischerite group in particular, we noted that the structural information of despujolsite needed to be improved.

The structure of despujolsite consists of layers of CaO₈ polyhedra (m.. symmetry), interconnected by Mn(OH)₆ octahedra (32. symmetry) and SO₄ tetrahedra (3.. symmetry). The average Mn—O bond length is 1.915 Å (Table 1). Calculations of bond-valence sums using the parameters from Brese & O'Keeffe (1991) yield 3.86 (v.u.) for Mn, indicating that the assigned valence of 4+ for Mn is consistent with the structure. The average S—O bond length is 1.472 Å. Ca atoms are eight coordinated with 4 (OH)^- ions, 2 H₂O molecules, and 2 O atoms. The average Ca—O bond length is 2.489 Å. There are two distinct hydrogen bonds: OH3—H1···O2 and OW4—H2··· O1 (Table 2).

The isostructural mineral fleischerite was previously modeled (Otto, 1975) with a split site for the O1 position. Similarly, studies of the sulfate mineral, barite BaSO₄, refined the O atoms that lie on special positions with a split atom model (Hill, 1977). However, Hill notes that there are no significant improvements in the refinement with a split-site model over the symmetry-constrained model. Further structure refinement with significantly better data by Jacobsen et al. (1998) led to a TLS (translation, libration, and screw motions) rigid body analysis (Downs, 2000) of the sulfate group. The results indicated that the SO₄ group behaves as a rigid body with significant translational and librational motions, demonstrating that the O atom sites are not split and that the large sizes of the displacement parameters are due entirely to thermal motion.

In contrast to the fleischerite study, our refinement of despujolsite did not indicate a split site. A TLS analysis of the displacement parameters indicate that the SO₄ group in despujolsite behaves likewise as a rigid body with a translational amplitude of 0.72 Å and a large libration angle of 7.95°. The libration angle for the SO₄ group in despujolsite, which is consistent with the 7°-8° range found in celestine, anglesite, and barite, indicates that the S–O bond lengths are ~0.009Å longer than their apparent values. If the libration angle is also large in fleischerite, then this may account for the effectiveness of splitting the O1 site, but our study indicates that the O1 site in fleischerite may not actually split.

Related literature

For the previous determination of the despujolsite crystal structure, see: Gaudefroy et al. (1968). For background to fleischerite, see: Otto (1975). For the crystal structures of sulfate minerals with split O sites, see: Hill (1977); Jacobsen et al. (1998). For TLS (translation, libration, and screw motions) rigid-body analysis, see: Downs (2000). Parameters for bond-valence analysis were taken from Brese & O'Keeffe (1991).

S2. Experimental

The despujolsite specimen used in this study is from N'Chwaning III mine, Kalahari Manganese field, Northern Cape Province, South Africa and is in the collection of the RRUFF project (deposition No. R100208; http://rruff.info). The composition was determined with a CAMECA SX100 electron microprobe (http://rruff.info) on a single-crystal from the same parent sample as the crystal used for the collection of X-ray diffraction intensity data. Electron microprobe analysis (15 points) with a 15 K eV accelerating voltage, 20 nA beam current, and a 5 µm beam size yielded an empirical chemical formula Ca_3.45Mn⁴⁺_0.86(S_0.96O₄)₂(OH)₆^.3H₂O (based on 11 O atoms). Because despujolsite crystals are not stable under the electron beam, which has also been observed by Gaudefroy et al. (1968), the electron microprobe data were used only for the estimation of cation ratios. The actual composition was determined by a combination of microprobe and X-ray structural analyses. Details of the sample chemistry and structural formula calculations can be found on the RRUFF Project website (http://rruff.info/R100208).

S3. Refinement

The H atoms were located from difference Fourier maps and their positions were refined with isotropic displacement parameters. The final refinement assumed an ideal chemistry, as the overall effects of the trace amount of Fe and Si on the final structure results are negligible. The highest residual peak in the difference Fourier maps was located 0.66 Å from O1, and the deepest hole was located 0.40 Å from Mn.

Computing details

Data collection: APEX2 (Bruker, 2003); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008b); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008b); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: SHELXTL (Sheldrick, 2008b).

Figures

	Fig. 1. The crystal structure of despujolsite. Yellow tetrahedra represent SO4 groups. Blue octahedra and purple polyhedra represent Mn(OH)6 groups and Ca(O,OH,H2O)8 groups, respectively. Light blue spheres represent H1 and H2.
	Fig. 2. Atoms in despujolsite with corresponding ellipsoids at 99% probability. SO4 groups are treated as rigid bodies and shown as yellow tetrahedra. Blue, purple, and red ellipsoids represent Mn, Ca, and O atoms, respectively. Hydrogen atoms are shown as light-blue spheres.
	Fig. 3. H-bonding interactions in despujolsite. Yellow tetrahedra represent SO4 groups. Purple polyhedra represent Ca(O,OH,H2O)8 groups. Red ellipsoids and blue spheres represent O and H atoms, respectively.

tricalcium manganese bis(sulfate) hexahydroxide trihydrate

Crystal data

Ca3Mn(SO4)2(OH)6·3H2O	Dx = 2.546 Mg m^−3
Mr = 523.40	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P62c	Cell parameters from 1145 reflections
Hall symbol: P -6c -2c	θ = 2.8–32.0°
a = 8.5405 (5) Å	µ = 2.49 mm^−1
c = 10.8094 (9) Å	T = 293 K
V = 682.81 (8) Å^3	Euhedral, yellow
Z = 2	0.07 × 0.06 × 0.04 mm
F(000) = 530

Data collection

Bruker APEXII CCD area-detector diffractometer	871 independent reflections
Radiation source: fine-focus sealed tube	758 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
ϕ and ω scans	θmax = 32.6°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 2008a)	h = −12→11
Tmin = 0.845, Tmax = 0.907	k = −12→12
6018 measured reflections	l = −16→15

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.024	w = 1/[σ^2(Fo^2) + (0.0113P)^2 + 0.2266P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.048	(Δ/σ)max < 0.001
S = 1.06	Δρmax = 0.45 e Å^−3
871 reflections	Δρmin = −0.30 e Å^−3
49 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0142 (11)
0 constraints	Absolute structure: Flack (1983), 305 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.0 (9)
Secondary atom site location: difference Fourier map

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Mn	0.0000	0.0000	0.0000	0.00846 (12)
Ca	0.1521 (3)	0.30348 (5)	0.2500	0.01085 (10)
S	0.3333	0.6667	0.02544 (5)	0.00936 (12)
O1	0.3333	0.6667	−0.11153 (15)	0.0167 (4)
O2	0.2419 (10)	0.47842 (15)	0.06891 (10)	0.0188 (3)
OH3	0.8945 (8)	0.0966 (8)	0.11070 (10)	0.0109 (3)
OW4	0.5006 (12)	0.4853 (12)	0.2500	0.0171 (5)
H1	0.836 (6)	0.125 (6)	0.076 (2)	0.026 (8)*
H2	0.521 (9)	0.445 (9)	0.193 (2)	0.046 (10)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mn	0.00919 (15)	0.00919 (15)	0.0070 (2)	0.00460 (8)	0.000	0.000
Ca	0.0137 (10)	0.00918 (19)	0.00980 (16)	0.0058 (10)	0.000	0.000
S	0.01001 (16)	0.01001 (16)	0.0081 (2)	0.00501 (8)	0.000	0.000
O1	0.0213 (6)	0.0213 (6)	0.0075 (7)	0.0107 (3)	0.000	0.000
O2	0.027 (3)	0.0106 (5)	0.0170 (5)	0.008 (2)	0.004 (3)	0.0033 (4)
OH3	0.0084 (15)	0.0148 (19)	0.0107 (4)	0.0067 (6)	−0.0006 (16)	−0.0004 (16)
OW4	0.019 (2)	0.023 (2)	0.0136 (6)	0.0138 (12)	0.000	0.000

Geometric parameters (Å, º)

Mn—OH3^i	1.9149 (11)	Ca—OH3^viii	2.456 (5)
Mn—OH3^ii	1.9149 (11)	Ca—OH3^iii	2.518 (5)
Mn—OH3^iii	1.9149 (11)	Ca—OH3^ix	2.518 (5)
Mn—OH3^iv	1.9149 (11)	Ca—OW4	2.578 (9)
Mn—OH3^v	1.9149 (11)	Ca—OW4^x	2.690 (9)
Mn—OH3^vi	1.9149 (11)	S—O2^x	1.4697 (11)
Ca—O2^vii	2.3465 (11)	S—O2^xi	1.4697 (11)
Ca—O2	2.3465 (11)	S—O2	1.4697 (11)
Ca—OH3^i	2.456 (5)	S—O1	1.4806 (18)
OH3^i—Mn—OH3^ii	177.7 (4)	OH3^ii—Mn—OH3^vi	85.08 (5)
OH3^i—Mn—OH3^iii	85.08 (5)	OH3^iii—Mn—OH3^vi	96.5 (3)
OH3^ii—Mn—OH3^iii	93.4 (3)	OH3^iv—Mn—OH3^vi	177.7 (4)
OH3^i—Mn—OH3^iv	85.08 (5)	OH3^v—Mn—OH3^vi	85.08 (5)
OH3^ii—Mn—OH3^iv	96.5 (3)	O2^x—S—O2^xi	110.28 (5)
OH3^iii—Mn—OH3^iv	85.08 (5)	O2^x—S—O2	110.28 (5)
OH3^i—Mn—OH3^v	96.5 (3)	O2^xi—S—O2	110.28 (5)
OH3^ii—Mn—OH3^v	85.08 (5)	O2^x—S—O1	108.65 (5)
OH3^iii—Mn—OH3^v	177.7 (4)	O2^xi—S—O1	108.65 (5)
OH3^iv—Mn—OH3^v	93.4 (3)	O2—S—O1	108.65 (5)
OH3^i—Mn—OH3^vi	93.4 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
OH3—H1···O2^xii	0.75 (2)	2.11 (2)	2.8193 (16)	158 (3)
OW4—H2···O1^xiii	0.77 (2)	2.10 (2)	2.7892 (18)	150 (3)

Symmetry codes: (xii) −x+1, −x+y, −z; (xiii) y, x, −z.