catena-Poly[[cobalt(II)-μ-aqua-μ-propano­ato-κ2O:O′-μ-propano­ato-κ2O:O] monohydrate]

Fischer, A.I.; Gurzhiy, V.V.; Belyaev, A.N.

doi:10.1107/S1600536810043540

metal-organic compounds

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ISSN: 2056-9890

Volume 66| Part 11| November 2010| Page m1498

https://doi.org/10.1107/S1600536810043540

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catena-Poly[[cobalt(II)-μ-aqua-μ-propanoato-κ²O:O′-μ-propanoato-κ²O:O] monohydrate]

A. I. Fischer,^a ^* V. V. Gurzhiy ^b ‡ and A. N. Belyaev ^a

^aSt Petersburg State Institute of Technology, Moskovsky Prospekt 26, 190013 St Petersburg, Russian Federation, and ^bSt Petersburg State University, Universitetskaya Naberezhnaya 7/9, 199034 St Petersburg, Russian Federation
^*Correspondence e-mail: andreasfischer@mail.ru

(Received 20 October 2010; accepted 25 October 2010; online 31 October 2010)

The title compound, {[Co(C₂H₅COO)₂(H₂O)]·H₂O}_n, was synthesized by the reaction of cobalt(II) carbonate hydrate with aqueous propionic acid. The structure consists of polymeric infinite linear chains with composition [Co(C₂H₅COO)_4/2(H₂O)_2/2]_∞ running along [010]. The chains are formed by Co²⁺ ions linked with bridging propionate groups and water molecules, with a Co⋯Co distance along the chains of 3.2587 (9) Å. The Co²⁺ ion is six-coordinated in a strongly distorted octahedral geometry. The chains are connected to each other by a network of O—H⋯O hydrogen bonds involving solvent water molecules.

Related literature

For the related cobalt(II) acetate dihydrate, see: Jiao et al. (2000 ). For the structure of a hydrated cobalt(II) acetate which has been isolated in similar conditions, see: Sobolev et al. (2003 ). For properties and applications of cobalt carboxylates, see: Eremenko et al. (2009 ); Gates (1992 ); Parshall & Ittel (1992 ); Partenheimer (1995 ).

Experimental

Crystal data

[Co(C₃H₅O₂)₂(H₂O)]·H₂O
M_r = 241.10
Monoclinic, C 2/c
a = 13.997 (4) Å
b = 6.4987 (18) Å
c = 21.440 (6) Å
β = 103.216 (5)°
V = 1898.6 (9) Å³
Z = 8
Mo Kα radiation
μ = 1.81 mm⁻¹
T = 170 K
0.5 × 0.3 × 0.2 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2007 ) T_min = 0.276, T_max = 0.332
11986 measured reflections
2762 independent reflections
2542 reflections with I > 2σ(I)
R_int = 0.032

Refinement

R[F² > 2σ(F²)] = 0.026
wR(F²) = 0.067
S = 1.09
2762 reflections
130 parameters
5 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.41 e Å⁻³
Δρ_min = −0.57 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H11⋯O6ⁱ	0.92 (3)	1.72 (3)	2.620 (2)	163 (3)
O1—H12⋯O5	0.89 (3)	1.78 (3)	2.660 (2)	171 (3)
O5—H51⋯O4ⁱⁱ	0.92 (3)	1.90 (3)	2.794 (2)	163 (3)
O5—H52⋯O2ⁱⁱⁱ	0.87 (3)	1.91 (3)	2.773 (2)	174 (3)
Symmetry codes: (i) x, y+1, z; (ii) $[-x+1, y, -z+{\script{1\over 2}}]$ ; (iii) $[-x+1, y+1, -z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2009 ); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536810043540/fj2358sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810043540/fj2358Isup2.hkl

checkCIF report

Comment top

Cobalt carboxylates are of great importance because of their application in homogeneous oxidation catalysis (Gates, 1992; Parshall & Ittel, 1992; Partenheimer, 1995), and their interesting magnetic properties (Eremenko et al., 2009). Carboxylate ligands coordinated to transition metal ions can adopt different binding modes and form a great number of various cage complexes and a variety of different one-dimensional, two-dimensional and three-dimensional structures.

The title compound, [Co(C₂H₅COO)₂(H₂O)]_n.nH₂O (I), actually named as cobalt(II) propionate dihydrate, is attracting our attention as the starting substance for the synthesis of mixed-valence cobalt carboxylates. This salt was synthesized and its crystal structure is reported herein.

The crystal structure of (I) contains one symmetrically independent Co²⁺ cation coordinated to four O atoms of four bridging propionates and two O atoms of bridging water molecules in a strongly distorted octahedral coordination (Fig. 1). The cis-angles about the Co atom range from 77.35 (4) to 109.40 (5)°, the Co—O bond length ranges from 2.0406 (12) to 2.2460 (12) Å; this is in agreement with the angles and the distances in isostructural cobalt(II) acetate dihydrate (Jiao et al., 2000). The structure of (I) consists of polymeric infinite linear chains with composition _∞[Co(C₂H₅COO)_4/2(H₂O)_2/2] running along [010]. The Co···Co separation is 3.2587 (9) Å. The bridging carboxylate groups adopt two coordination modes, monodentate and syn-syn bidentate. The bidentate carboxylate group has C—O bonds of equal length, 1.267 (2) Å, whereas monodentate carboxylate group has different C—O bond lengths, 1.235 (2) and 1.305 (2) Å. The chains are connected to each other by a network of hydrogen bonds to solvate water molecules (Fig. 2).

It is rather interesting that the use of acetic acid instead of propionic acid in the synthesis of (I) result in the formation of monomeric cobalt(II) acetate tetrahydrate (Sobolev et al., 2003), and the polymeric cobalt(II) acetate dihydrate is formed by recrystallization of cobalt(II) acetate tetrahydrate from acetic acid (Jiao et al., 2000).

Related literature top

For the isostructural cobalt(II) acetate dihydrate, see: Jiao et al. (2000). For the structure of a hydrated cobalt(II) acetate which has been isolated in similar conditions, see: Sobolev et al. (2003). For properties and applications of cobalt carboxylates, see: Eremenko et al. (2009); Gates (1992); Parshall & Ittel (1992); Partenheimer (1995).

Experimental top

To a solution of propionic acid (7.4 g, 100 mmol) in water (15 ml), an excess of fresh cobalt(II) carbonate hydrate, CoCO₃.xH₂O, (8.0 g, approximately 60 mmol) was added. The reaction mixture was stirred for 8 h at room temperature, followed by filtrating the unreacted CoCO₃.xH₂O out. The filtrate was allowed to stand at room temperature for slow evaporation. The red single crystals of (I) suitable for X-ray diffraction studies were obtained after several days. Yield 85%.

Structure description top

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. The coordinated mode and linkage of the complex (I). Displacement ellipsoids of non-H atoms are drawn at the 40% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius. Symmetry codes: i = –x + 1/2, y + 1/2,–z + 1/2; ii = –x + 1/2, y–1/2, –z + 1/2.]
	Fig. 2. Sticks representation of the crystal structure of (I) showing hydrogen bonds as green dashed lines. Only the H atoms involved in hydrogen bonds are shown. Co atoms are blue, O atoms are red, C atoms are grey, and selected H atoms are green colored.]

catena-Poly[[cobalt(II)-µ-aqua-µ-propanoato-κ²O:O'- µ-propanoato-κ²O:O] monohydrate] top

Crystal data top

[Co(C₃H₅O₂)₂(H₂O)]·H₂O	F(000) = 1000
M_r = 241.10	D_x = 1.687 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 7703 reflections
a = 13.997 (4) Å	θ = 2.9–35.9°
b = 6.4987 (18) Å	µ = 1.81 mm⁻¹
c = 21.440 (6) Å	T = 170 K
β = 103.216 (5)°	Prism, red
V = 1898.6 (9) Å³	0.5 × 0.3 × 0.2 mm
Z = 8

Data collection top

Bruker APEXII CCD diffractometer	2762 independent reflections
Radiation source: fine-focus sealed tube	2542 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.032
φ and ω scans	θ_max = 30.0°, θ_min = 2.0°
Absorption correction: multi-scan (SADABS; Bruker, 2007)	h = −19→19
T_min = 0.276, T_max = 0.332	k = −9→9
11986 measured reflections	l = −30→30

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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.067	H atoms treated by a mixture of independent and constrained refinement
S = 1.09	w = 1/[σ²(F_o²) + (0.0329P)² + 1.4667P] where P = (F_o² + 2F_c²)/3
2762 reflections	(Δ/σ)_max < 0.001
130 parameters	Δρ_max = 0.41 e Å⁻³
5 restraints	Δρ_min = −0.57 e Å⁻³

Crystal data top

[Co(C₃H₅O₂)₂(H₂O)]·H₂O	V = 1898.6 (9) Å³
M_r = 241.10	Z = 8
Monoclinic, C2/c	Mo Kα radiation
a = 13.997 (4) Å	µ = 1.81 mm⁻¹
b = 6.4987 (18) Å	T = 170 K
c = 21.440 (6) Å	0.5 × 0.3 × 0.2 mm
β = 103.216 (5)°

Data collection top

Bruker APEXII CCD diffractometer	2762 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2007)	2542 reflections with I > 2σ(I)
T_min = 0.276, T_max = 0.332	R_int = 0.032
11986 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.026	5 restraints
wR(F²) = 0.067	H atoms treated by a mixture of independent and constrained refinement
S = 1.09	Δρ_max = 0.41 e Å⁻³
2762 reflections	Δρ_min = −0.57 e Å⁻³
130 parameters

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 > 2σ(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	U_iso*/U_eq
Co1	0.248706 (13)	0.18331 (3)	0.244111 (9)	0.01830 (7)
O1	0.29927 (8)	0.44228 (16)	0.19444 (5)	0.0231 (2)
H11	0.267 (2)	0.511 (5)	0.1580 (14)	0.080*
H12	0.362 (2)	0.441 (5)	0.1918 (16)	0.080*
O2	0.39246 (8)	−0.23440 (17)	0.29662 (6)	0.0262 (2)
O3	0.23831 (8)	−0.08151 (15)	0.18689 (5)	0.0217 (2)
O4	0.39309 (8)	0.10838 (17)	0.28586 (5)	0.0246 (2)
O5	0.47910 (10)	0.4367 (2)	0.17307 (8)	0.0391 (3)
H51	0.516 (2)	0.328 (5)	0.1935 (15)	0.080*
H52	0.517 (2)	0.543 (4)	0.1846 (16)	0.080*
O6	0.21765 (10)	−0.29849 (19)	0.10436 (6)	0.0338 (3)
C1	0.53359 (12)	−0.0526 (3)	0.35261 (9)	0.0304 (3)
H1A	0.5732	0.0598	0.3390	0.046*
H1B	0.5683	−0.1860	0.3505	0.046*
C2	0.21658 (11)	−0.1222 (2)	0.12565 (7)	0.0229 (3)
C3	0.1606 (2)	0.0073 (4)	0.01094 (10)	0.0580 (7)
H3A	0.1450	0.1368	−0.0146	0.087*
H3B	0.1013	−0.0834	0.0029	0.087*
H3C	0.2157	−0.0660	−0.0021	0.087*
C4	0.52401 (19)	−0.0140 (5)	0.42103 (11)	0.0600 (7)
H4A	0.5908	−0.0101	0.4503	0.090*
H4B	0.4847	−0.1272	0.4346	0.090*
H4C	0.4902	0.1206	0.4231	0.090*
C5	0.43274 (11)	−0.0596 (2)	0.30805 (7)	0.0208 (3)
C6	0.19027 (18)	0.0594 (3)	0.08116 (9)	0.0418 (5)
H6A	0.1351	0.1358	0.0932	0.063*
H6B	0.2480	0.1544	0.0881	0.063*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Co1	0.01681 (10)	0.01335 (10)	0.02365 (11)	0.00019 (7)	0.00237 (7)	0.00019 (7)
O1	0.0216 (5)	0.0199 (5)	0.0281 (5)	0.0003 (4)	0.0061 (4)	0.0025 (4)
O2	0.0192 (5)	0.0173 (5)	0.0387 (6)	−0.0008 (4)	−0.0006 (4)	0.0004 (4)
O3	0.0247 (5)	0.0170 (5)	0.0221 (5)	0.0004 (4)	0.0026 (4)	0.0003 (4)
O4	0.0185 (5)	0.0181 (5)	0.0347 (6)	0.0001 (4)	0.0010 (4)	0.0004 (4)
O5	0.0241 (6)	0.0228 (6)	0.0687 (10)	0.0001 (5)	0.0068 (6)	0.0011 (6)
O6	0.0486 (8)	0.0254 (6)	0.0255 (5)	0.0056 (5)	0.0044 (5)	−0.0032 (4)
C1	0.0188 (7)	0.0231 (8)	0.0443 (9)	0.0001 (6)	−0.0034 (6)	0.0012 (6)
C2	0.0225 (7)	0.0225 (7)	0.0234 (6)	0.0027 (6)	0.0043 (5)	0.0012 (5)
C3	0.089 (2)	0.0507 (13)	0.0271 (9)	0.0158 (13)	−0.0012 (10)	0.0075 (9)
C4	0.0477 (13)	0.0883 (19)	0.0351 (10)	−0.0161 (13)	−0.0093 (9)	0.0042 (12)
C5	0.0170 (6)	0.0199 (7)	0.0253 (6)	0.0002 (5)	0.0044 (5)	−0.0005 (5)
C6	0.0667 (14)	0.0300 (9)	0.0270 (8)	0.0139 (9)	0.0069 (8)	0.0065 (7)

Geometric parameters (Å, º) top

Co1—O2ⁱ	2.0406 (12)	C1—C5	1.514 (2)
Co1—O4	2.0726 (12)	C1—C4	1.524 (3)
Co1—O3	2.0991 (11)	C1—H1A	1.0000
Co1—O3ⁱ	2.1058 (11)	C1—H1B	1.0000
Co1—O1	2.1936 (12)	C2—C6	1.509 (2)
Co1—O1ⁱⁱ	2.2460 (12)	C3—C6	1.506 (3)
O1—H11	0.92 (3)	C3—H3A	1.0000
O1—H12	0.89 (3)	C3—H3B	1.0000
O2—C5	1.2669 (18)	C3—H3C	1.0000
O3—C2	1.3053 (18)	C4—H4A	1.0000
O4—C5	1.2670 (18)	C4—H4B	1.0000
O5—H51	0.92 (3)	C4—H4C	1.0000
O5—H52	0.87 (3)	C6—H6A	1.0000
O6—C2	1.2346 (19)	C6—H6B	1.0000

O2ⁱ—Co1—O4	178.40 (4)	C4—C1—H1A	109.7
O2ⁱ—Co1—O3	91.94 (5)	C5—C1—H1B	109.7
O4—Co1—O3	89.44 (4)	C4—C1—H1B	109.7
O2ⁱ—Co1—O3ⁱ	91.72 (5)	H1A—C1—H1B	108.2
O4—Co1—O3ⁱ	87.03 (4)	O6—C2—O3	122.70 (14)
O3—Co1—O3ⁱ	171.46 (4)	O6—C2—C6	120.92 (14)
O2ⁱ—Co1—O1	88.83 (5)	O3—C2—C6	116.38 (14)
O4—Co1—O1	89.94 (5)	C6—C3—H3A	109.5
O3—Co1—O1	109.40 (5)	C6—C3—H3B	109.5
O3ⁱ—Co1—O1	78.38 (5)	H3A—C3—H3B	109.5
O2ⁱ—Co1—O1ⁱⁱ	92.50 (5)	C6—C3—H3C	109.5
O4—Co1—O1ⁱⁱ	88.60 (5)	H3A—C3—H3C	109.5
O3—Co1—O1ⁱⁱ	77.35 (4)	H3B—C3—H3C	109.5
O3ⁱ—Co1—O1ⁱⁱ	94.79 (5)	C1—C4—H4A	109.5
O1—Co1—O1ⁱⁱ	173.08 (3)	C1—C4—H4B	109.5
Co1—O1—Co1ⁱ	94.44 (5)	H4A—C4—H4B	109.5
Co1—O1—H11	129 (2)	C1—C4—H4C	109.5
Co1ⁱ—O1—H11	90 (2)	H4A—C4—H4C	109.5
Co1—O1—H12	117 (2)	H4B—C4—H4C	109.5
Co1ⁱ—O1—H12	118 (2)	O2—C5—O4	124.23 (14)
H11—O1—H12	104 (3)	O2—C5—C1	117.31 (13)
C5—O2—Co1ⁱⁱ	131.47 (10)	O4—C5—C1	118.44 (13)
C2—O3—Co1	136.31 (10)	C3—C6—C2	115.31 (17)
C2—O3—Co1ⁱⁱ	121.50 (10)	C3—C6—H6A	108.4
Co1—O3—Co1ⁱⁱ	101.60 (5)	C2—C6—H6A	108.4
C5—O4—Co1	131.66 (10)	C3—C6—H6B	108.4
H51—O5—H52	104 (3)	C2—C6—H6B	108.4
C5—C1—C4	109.75 (16)	H6A—C6—H6B	107.5
C5—C1—H1A	109.7

Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) −x+1/2, y−1/2, −z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H11···O6ⁱⁱⁱ	0.92 (3)	1.72 (3)	2.620 (2)	163 (3)
O1—H12···O5	0.89 (3)	1.78 (3)	2.660 (2)	171 (3)
O5—H51···O4^iv	0.92 (3)	1.90 (3)	2.794 (2)	163 (3)
O5—H52···O2^v	0.87 (3)	1.91 (3)	2.773 (2)	174 (3)

Symmetry codes: (iii) x, y+1, z; (iv) −x+1, y, −z+1/2; (v) −x+1, y+1, −z+1/2.

Experimental details

Crystal data
Chemical formula	[Co(C₃H₅O₂)₂(H₂O)]·H₂O
M_r	241.10
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	170
a, b, c (Å)	13.997 (4), 6.4987 (18), 21.440 (6)
β (°)	103.216 (5)
V (Å³)	1898.6 (9)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	1.81
Crystal size (mm)	0.5 × 0.3 × 0.2

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2007)
T_min, T_max	0.276, 0.332
No. of measured, independent and observed [I > 2σ(I)] reflections	11986, 2762, 2542
R_int	0.032
(sin θ/λ)_max (Å⁻¹)	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.067, 1.09
No. of reflections	2762
No. of parameters	130
No. of restraints	5
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.41, −0.57

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2008), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H11···O6ⁱ	0.923 (28)	1.723 (30)	2.620 (2)	163 (3)
O1—H12···O5	0.893 (30)	1.775 (31)	2.660 (2)	171 (3)
O5—H51···O4ⁱⁱ	0.924 (30)	1.896 (30)	2.794 (2)	163 (3)
O5—H52···O2ⁱⁱⁱ	0.872 (26)	1.905 (26)	2.773 (2)	174 (3)

Symmetry codes: (i) x, y+1, z; (ii) −x+1, y, −z+1/2; (iii) −x+1, y+1, −z+1/2.

Footnotes

‡Additional correspondence author, e-mail: vladgeo17@mail.ru.

References

Brandenburg, K. (2008). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Bruker (2007). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker, (2009). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Eremenko, I. L., Sidorov, A. A. & Kiskin, M. A. (2009). Magnetic Nanoparticles, edited by S. P. Gubin, pp. 349–391. Weinheim: Wiley-VCH. Google Scholar
Gates, B. C. (1992). Catalytic Chemistry. New York: Wiley-Interscience. Google Scholar
Jiao, X.-D., Guzei, I. A. & Espenson, J. H. (2000). Z. Kristallogr. New Cryst. Struct. 215, 173–174. CAS Google Scholar
Parshall, G. W. & Ittel, S. D. (1992). Homogenous Catalysis. New York: Wiley-Interscience. Google Scholar
Partenheimer, W. (1995). Catal. Today, 23, 69–158. CrossRef CAS Web of Science Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sobolev, A. N., Miminoshvili, E. B., Miminoshvili, K. E. & Sakvarelidze, T. N. (2003). Acta Cryst. E59, m836–m837. Web of Science CSD CrossRef IUCr Journals Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar

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