A quarter of a century after its synthesis and with >200 papers based on its use, `Co(CO₃)_0.5(OH)·0.11H₂O′ proves to be Co₆(CO₃)₂(OH)₈·H₂O from synchrotron powder diffraction data

The successful attempt to solve the crystal structure of Co(CO₃)_0.5(OH)·0.11H₂O (denoted CCH), based on synchrotron powder diffraction data, leads to a drastic revision of the chemical formula to Co₆(CO₃)₂(OH)₈·H₂O [hexa­cobalt(II) bis­(carbonate) octa­hydroxide monohydrate] and to a hexa­gonal cell instead of the ortho­rhom­bic cell suggested previously [Porta et al. (1992). J. Chem. Soc. Faraday Trans. 88, 311–319]. This results in a new structure-type related to malachite involving infinite chains of [CoO₆] octa­hedra sharing edges along a short c axis, delimiting tunnels having a three-branched star section. All reports discussing cobalt hy­droxy­carbonates (CCH) without any structural knowledge and especially its topotactic decomposition into Co₃O₄ have, as a result, to be reconsidered.

Computing details

Program(s) used to solve structure: McMaille (Le Bail, 2004) and ESPOIR (Le Bail, 2001); program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 1993); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: publCIF (Westrip, 2010).

Hexacobalt(II) bis(carbonate) octahydroxide monohydrate

Crystal data

Co6(CO3)2(OH)8·H2O	Dx = 3.617 Mg m^−3
Mr = 627.69	Synchrotron radiation, λ = 0.807700 Å
Hexagonal, P62m	µ = 12.06 mm^−1
Hall symbol: P -6 -2	T = 293 K
a = 10.3236 (4) Å	Particle morphology: powder of nanoneedles
c = 3.12244 (15) Å	light pink
V = 288.20 (2) Å^3	cylinder, 0.5 × 0.5 mm
Z = 1	Specimen preparation: Prepared at 293 K
F(000) = 304

Data collection

MAR345dif diffractometer	Data collection mode: transmission
Radiation source: synchrotron	Scan method: step
Specimen mounting: quartz capillary	2θmin = 3.883°, 2θmax = 58.870°, 2θstep = 0.020°

Refinement

Rp = 3.714	50 parameters
Rwp = 4.827	0 restraints
Rexp = 2.465	H-atom parameters not refined
RBragg = 3.948	(Δ/σ)max < 0.001
2805 data points

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Co1	0.42427 (12)	0.00000	0.00000	0.0180 (4)*
Co2	0.36174 (19)	0.2336 (2)	0.50000	0.0328 (7)*	0.500
O1	0.5360 (4)	0.2464 (4)	0.00000	0.0278 (9)*
O2	0.1908 (5)	0.1908 (5)	0.00000	0.0278 (9)*
O3	0.5545 (6)	0.00000	0.50000	0.0278 (9)*
O4	0.2852 (7)	0.00000	0.50000	0.0278 (9)*
C1	0.66667	0.33333	0.00000	0.0278 (9)*

Geometric parameters (Å, º)

Co1—O1	2.206 (4)	Co2—O1^iii	2.335 (4)
Co1—O3	2.060 (4)	Co2—O2	2.229 (4)
Co1—O4	2.121 (5)	Co2—O4	2.130 (2)
Co1—O3^i	2.060 (4)	Co2—O2^iii	2.229 (4)
Co1—O4^i	2.121 (5)	Co2—O3^iv	1.908 (6)
Co1—O1^ii	2.206 (4)	O1—C1	1.189 (4)
Co2—O1	2.335 (4)
O1—Co1—O3	92.01 (8)	Co2—O2—Co2^i	88.9 (2)
O1—Co1—O4	87.92 (8)	Co2—O2—Co2^v	120.7 (2)
O1—Co1—O3^i	92.01 (8)	Co2—O2—Co2^vi	61.87 (10)
O1—Co1—O4^i	87.92 (8)	Co2^i—O2—Co2^v	61.87 (10)
O1—Co1—O1^ii	173.9 (2)	Co2^i—O2—Co2^vi	120.7 (2)
O3—Co1—O4	83.34 (19)	Co2^v—O2—Co2^vi	88.94 (17)
O3—Co1—O3^i	98.53 (19)	Co1—O3—Co1^iii	98.5 (3)
O3—Co1—O4^i	178.1 (2)	Co1—O3—Co2^vii	121.46 (6)
O1^ii—Co1—O3	92.01 (11)	Co1—O3—Co2^viii	121.46 (6)
O3^i—Co1—O4	178.1 (2)	Co1^iii—O3—Co2^vii	121.46 (6)
O4—Co1—O4^i	94.8 (2)	Co1^iii—O3—Co2^viii	121.46 (6)
O1^ii—Co1—O4	87.92 (12)	Co2^vii—O3—Co2^viii	73.8 (3)
O3^i—Co1—O4^i	83.34 (19)	Co1—O4—Co2	97.59 (11)
O1^ii—Co1—O3^i	92.01 (11)	Co1—O4—Co1^iii	94.8 (3)
O1^ii—Co1—O4^i	87.92 (12)	Co1—O4—Co2^ix	97.60 (12)
O2—Co2—O4	88.10 (19)	Co1^iii—O4—Co2	97.59 (11)
O2—Co2—O2^iii	88.94 (17)	Co2—O4—Co2^ix	157.5 (4)
O2—Co2—O3^iv	95.0 (2)	Co1^iii—O4—Co2^ix	97.60 (12)
O2^iii—Co2—O4	88.10 (19)	O1—C1—O1^x	120.0 (4)
O3^iv—Co2—O4	175.6 (3)	O1—C1—O1^vii	120.0 (3)
O2^iii—Co2—O3^iv	95.0 (2)	O1^x—C1—O1^vii	120.0 (4)
Co1—O1—C1	127.7 (3)
O3—Co1—O1—C1	49.31 (13)	O3—Co1—O4—Co2	98.33 (17)
O4—Co1—O1—C1	132.56 (15)	O2—Co2—O4—Co1	87.6 (2)
O1—Co1—O4—Co2	6.07 (19)

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

Valence bond analysis according to the empirical expression from Brown and Altermatt [Brown, I. D. and Altermatt, D. (1985). Acta Cryst. B41, 244–247], using parameters for solids from Brese and O'Keeffe [Brese, N. E. and O'Keeffe, M. (1991). Acta Cryst. B47, 192–197]. The valence deficit observed for atoms O2, O3 and O4 is expected to be compensated by hydrogen bonding and the water molecule would be preferentially located on the O2 site.

	O1	O2	O3	O4	Σ	Σ(expected)
Co1	0.245 × 2		0.363 × 2	0.308 × 2	1.83	2
			× 2	× 2
Co2	0.173 × 2	0.230 × 2	0.547	0.301	1.65	2
		× 2
C1	1.721 × 3				5.16	4
Σ	2.14	0.46	1.23	0.92
Σ(expected)	2	2	2	2