Cobaltaustinite, CaCo(AsO₄)(OH)

This study presents the first structural report of a natural cobaltaustinite sample (calcium cobalt arsenate hydroxide) based on single-crystal X-ray diffraction data. Cobaltaustinite, with the ideal formula CaCo(AsO₄)(OH), belongs to the adelite mineral group. The CoO₆ octa­hedra share edges to form chains extending parallel to the c axis, which are cross-linked by Ca²⁺ ions and by sharing vertices with isolated AsO₄ tetra­hedra. The Ca²⁺ ions are situated in square anti­prisms formed by eight O atoms. The major structural difference between the five calcium arsenates in the adelite group is shown in the bonding environments around the octa­hedrally coordinated M²⁺ cations (M = Cu, Zn, Co, Ni and Mg), with the average M—O distance decreasing from Cu—O in conichalcite, CaCu(AsO₄)(OH) to Zn—O in austinite, CaZn(AsO₄)(OH), Co—O in cobaltaustinite, Ni—O in nickelaustinite, CaNi(AsO₄)(OH), and Mg—O in adelite, CaMg(AsO₄)(OH). The donor–acceptor O—H...O distance [2.721 (7) Å] in cobaltaustinite is similar to those in austinite and nickelaustinite, but different from those in adelite and conichalcite.

Key indicators

• Single-crystal X-ray study
• T = 273 K
• Mean [sigma](o-O) = 0.005 Å
• R factor = 0.045
• wR factor = 0.078
• Data-to-parameter ratio = 16.8

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT112_ALERT_2_B ADDSYM Detects Additional (Pseudo) Symm. Elem...          m
PLAT112_ALERT_2_B ADDSYM Detects Additional (Pseudo) Symm. Elem...          m
PLAT115_ALERT_5_B ADDSYM Detects Noncrystallographic Inversion ...         87 PerFi

Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O5     -   H      ...       1.02 Ang.

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           32.50
           From the CIF: _reflns_number_total               1344
           Count of symmetry unique reflns          863
           Completeness (_total/calc)            155.74%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       481
           Fraction of Friedel pairs measured     0.557
           Are heavy atom types Z>Si present        yes

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

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 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
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

---

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XTALDRAW (Downs & Hall-Wallace, 2003); software used to prepare material for publication: SHELXTL (Bruker, 1997).

calcium cobalt arsenate hydroxide

Crystal data

CaCo(AsO4)(OH)	F(000) = 484
Mr = 255.17	Dx = 4.252 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 475 reflections
a = 7.4919 (9) Å	θ = 3.6–26.7°
b = 8.9946 (9) Å	µ = 13.79 mm^−1
c = 5.9158 (7) Å	T = 273 K
V = 398.65 (8) Å^3	Drusy coating, dark green
Z = 4	0.05 × 0.05 × 0.04 mm

Data collection

Bruker SMART APEX2 CCD area-detector diffractometer	1344 independent reflections
Radiation source: fine-focus sealed tube	870 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.062
φ and ω scans	θmax = 32.5°, θmin = 3.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2005)	h = −10→11
Tmin = 0.507, Tmax = 0.576	k = −13→13
5752 measured reflections	l = −7→8

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.045	All H-atom parameters refined
wR(F^2) = 0.078	w = 1/[σ^2(Fo^2)]
S = 0.98	(Δ/σ)max = 0.001
1344 reflections	Δρmax = 1.00 e Å^−3
80 parameters	Δρmin = −0.82 e Å^−3
0 restraints	Absolute structure: Flack (1983), with 488 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.01 (3)

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
Ca	0.62941 (19)	0.32886 (14)	0.5223 (3)	0.0166 (4)
Co	0.25814 (17)	0.50516 (13)	0.2547 (3)	0.0145 (3)
As	0.62045 (9)	0.67900 (7)	0.48441 (13)	0.0143 (2)
O1	0.4433 (5)	0.5613 (4)	0.5088 (9)	0.0210 (11)
O2	0.7125 (7)	0.4364 (5)	0.9121 (8)	0.0247 (13)
O3	0.3521 (6)	0.2695 (4)	0.7673 (9)	0.0181 (12)
O4	0.3975 (7)	0.2945 (5)	0.2403 (8)	0.0223 (12)
O5	0.3956 (6)	0.5740 (4)	0.9944 (10)	0.0218 (10)
H	0.504 (12)	0.506 (8)	0.990 (16)	0.06 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca	0.0151 (7)	0.0150 (6)	0.0197 (7)	0.0010 (6)	−0.0007 (6)	−0.0009 (6)
Co	0.0131 (5)	0.0157 (5)	0.0149 (5)	−0.0005 (4)	0.0009 (4)	0.0013 (4)
As	0.0119 (3)	0.0139 (3)	0.0172 (3)	−0.0003 (3)	0.0001 (3)	−0.0001 (3)
O1	0.019 (2)	0.022 (2)	0.022 (2)	−0.0043 (17)	−0.001 (2)	−0.008 (3)
O2	0.021 (3)	0.027 (3)	0.027 (3)	0.006 (2)	−0.004 (2)	−0.002 (2)
O3	0.018 (3)	0.018 (2)	0.018 (2)	0.000 (2)	−0.001 (2)	0.0021 (19)
O4	0.026 (3)	0.018 (2)	0.022 (2)	−0.001 (2)	−0.009 (2)	0.001 (2)
O5	0.017 (2)	0.026 (2)	0.023 (2)	0.0006 (19)	−0.004 (3)	0.001 (2)

Geometric parameters (Å, º)

Ca—O5^i	2.302 (4)	Co—O5^v	1.961 (5)
Ca—O4	2.428 (5)	Co—O1	2.107 (5)
Ca—O2^ii	2.507 (5)	Co—O4	2.165 (5)
Ca—O1	2.514 (4)	Co—O1^v	2.180 (5)
Ca—O3^iii	2.550 (5)	Co—O3^v	2.190 (4)
Ca—O2	2.577 (5)	As—O2^ii	1.682 (5)
Ca—O3	2.589 (5)	As—O3^vi	1.692 (5)
Ca—O4^iii	2.690 (6)	As—O4^vii	1.692 (5)
Co—O5^iv	1.953 (6)	As—O1	1.704 (4)
O5^i—Ca—O4	77.62 (17)	O3^iii—Ca—O4^iii	73.69 (14)
O5^i—Ca—O2^ii	149.97 (19)	O2—Ca—O4^iii	60.49 (15)
O4—Ca—O2^ii	105.45 (18)	O3—Ca—O4^iii	102.82 (15)
O5^i—Ca—O1	141.41 (15)	O5^iv—Co—O5^v	174.3 (2)
O4—Ca—O1	71.77 (16)	O5^iv—Co—O1	98.01 (19)
O2^ii—Ca—O1	63.48 (15)	O5^v—Co—O1	87.6 (2)
O5^i—Ca—O3^iii	71.27 (17)	O5^iv—Co—O4	89.6 (2)
O4—Ca—O3^iii	87.83 (17)	O5^v—Co—O4	89.64 (19)
O2^ii—Ca—O3^iii	78.95 (15)	O1—Co—O4	85.42 (18)
O1—Ca—O3^iii	129.05 (16)	O5^iv—Co—O1^v	85.7 (2)
O5^i—Ca—O2	115.58 (19)	O5^v—Co—O1^v	88.6 (2)
O4—Ca—O2	146.65 (18)	O1—Co—O1^v	176.2 (2)
O2^ii—Ca—O2	78.61 (10)	O4—Co—O1^v	93.88 (18)
O1—Ca—O2	81.39 (17)	O5^iv—Co—O3^v	86.11 (18)
O3^iii—Ca—O2	125.00 (18)	O5^v—Co—O3^v	95.17 (19)
O5^i—Ca—O3	75.73 (16)	O1—Co—O3^v	90.12 (18)
O4—Ca—O3	77.54 (15)	O4—Co—O3^v	173.3 (2)
O2^ii—Ca—O3	134.30 (14)	O1^v—Co—O3^v	90.89 (18)
O1—Ca—O3	75.18 (15)	O2^ii—As—O3^vi	115.3 (2)
O3^iii—Ca—O3	146.07 (8)	O2^ii—As—O4^vii	103.8 (2)
O2—Ca—O3	76.72 (16)	O3^vi—As—O4^vii	113.34 (19)
O5^i—Ca—O4^iii	70.88 (16)	O2^ii—As—O1	102.6 (2)
O4—Ca—O4^iii	147.17 (7)	O3^vi—As—O1	108.7 (2)
O2^ii—Ca—O4^iii	97.49 (16)	O4^vii—As—O1	112.7 (2)
O1—Ca—O4^iii	140.68 (16)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H···O2	1.02 (9)	1.74 (9)	2.721 (7)	159 (8)