Download citation
Download citation
link to html
Crystals of an­hydrous cadmium oxalate, β-[Cd(C2O4)], have been synthesized hydro­thermally and the crystal structure solved using single-crystal X-ray diffraction data. The Cd and oxalate ions lie about independent inversion centres. The structure consists of a three-dimensional framework built from sheets of cadmium octahedra linked together by oxalate groups.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101009581/br1339sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101009581/br1339Isup2.hkl
Contains datablock I

CCDC reference: 173338

Comment top

The assembly of metal-organic frameworks is currently an intense research topic and many one-, two- and three-dimensional structures have recently been characterized (Rao et al., 2001). Among the anions involved in the formation of such solids, the oxalate group, which possesses four donor O atoms, plays a major role. Indeed, it can act either as a monodentate or a bidentate chelating ligand and can thus bridge two or more metal atoms in a variety of arrangements, as recently shown with a few compounds (Bataille et al., 1999; Boudaren et al., 2000). Recent studies reported the crystal structures of SrC2O4 (Price et al., 1999) and PbC2O4 (Christensen et al., 1988), both prepared by direct synthesis. Almost all known anhydrous metal oxalates MC2O4 (M is Mn, Ni, Zn, Sn, Fe, Co or Cu; Kondrashev et al., 1985) result from thermal decomposition of the related hydrates (Naumov et al., 1996). Two types of structures have been established for CuC2O4 (Schmittler, 1968): an α disordered structure and a suggested structural model for a β ordered phase. Among the microcrystalline β phases, β-ZnC2O4 showed the best crystallization and its crystal structure was solved from powder diffraction data using 62 Bragg reflections (Kondrashev et al., 1985). In the course of our study of cadmium oxalate-based compounds (Jeanneau et al., 2001), we have synthesized a new anhydrous cadmium oxalate, CdC2O4, which differs from the oxalate obtained by decomposition of the trihydrate [Hanawalt et al., 1938; Powder Diffraction File No. 14–0712 (2000)]. The structure of this compound has been solved from single-crystal X-ray diffraction data and the results are presented here.

The title compound has a monoclinic unit cell with parameters close to those found for the β forms mentioned above [e.g. for M = Zn, a 5.831 (2), b 5.123 (2) and c 5.331 (2) Å, and β 113.20 (2)°]. The structure displays a similar arrangement of the MO6 octahedra and oxalate anions. It can either be described as inter-linked M-oxalate-M chains or as a layered material, as will be done here.

A cationic layer is built from corner-shared CdO6 octahedra running along [110] and [110]. The corrugated sheets, parallel to (101), are linked together via bidentate chelating oxalate groups lying in both (110) and (110) planes (Fig. 1). The Cd environment consists of six O atoms, all belonging to an oxalate group (Fig. 2). The polyhedron is a nearly regular octahedron, with three Cd—O distances in agreement with the mean distance of 2.296 (4) Å reported by Chung et al. (1995) for six-coordinate Cd atoms. The mean distances and angles within the oxalate group are close to the values reported by Hahn (1957) for different oxalate compounds. Moreover, the oxalate group is nearly planar, with a mean atomic deviation of 0.002 Å from the plane. The oxalate group in the isostructural compound β-ZnC2O4 was found to be highly distorted, with a significant deviation from planarity (up to 0.11 Å) and unequal C—O bond lengths (1.40 and 1.15 Å), which can easily be explained by the difficulty of obtaining precise results from the small number of structure factor amplitudes extracted from the powder diffraction pattern (Kondrashev et al., 1985).

The structure determination from single-crystal diffraction data described here shows that the title cadmium compound belongs to the isostructural family of anhydrous oxalates β-MC2O4 and reports a precise description of the structural model.

Experimental top

The synthesis of the title compound was carried out by hydrothermal reaction. Cd(NO3)2·4H2O (0.65 mmol), K2C2O4 (3.25 mmol) and water (8 ml) were placed in a Teflon-lined autoclave (Paar) at 423 K for 100 h. The mixture was then cooled to ambient temperature at 6 K h-1, leading to the formation of colourless bipyramidal crystals. These were washed with water and then ethanol, and dried in air. Thermogravimetric analyses and temperature-dependent X-ray diffraction showed that the compound decomposes at about 523 K to yield cubic CdO.

Refinement top

The magnitude of the minimal and maximal residual electron densities correspond to the deepest hole, located 0.65 Å from the Cd atom, and to the highest peak, located 1.57 Å from atom O1.

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR97 (Altomare et al., 1998); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. A polyhedral representation of the structure of β-CdC2O4 viewed along [101].
[Figure 2] Fig. 2. A view of the Cd environment in β-CdC2O4, with the atom-labelling scheme and 50% probability displacement ellipsoids [symmetry codes: (i) -x, -y, -z; (ii) x, y, z - 1; (iii) -x, -y, 1 - z; (iv) 1/2 + x, 1/2 - y, z - 1/2; (v) -1/2 - x, y - 1/2, 1/2 - z].
Anhydrous cadmium oxalate top
Crystal data top
CdC2O4F(000) = 184
Mr = 200.43Dx = 4.079 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 1867 reflections
a = 5.8260 (5) Åθ = 1.0–35.0°
b = 5.2520 (7) ŵ = 6.54 mm1
c = 5.8320 (7) ÅT = 293 K
β = 113.86 (2)°Lozenge, colourless
V = 163.19 (3) Å30.08 × 0.06 × 0.03 mm
Z = 2
Data collection top
Nonius KappaCCD area-detector
diffractometer
721 independent reflections
Radiation source: fine-focus sealed tube557 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.025
θ/2θ scansθmax = 34.9°, θmin = 4.2°
Absorption correction: integration
(Coppens, 1970)
h = 09
Tmin = 0.615, Tmax = 0.841k = 88
1314 measured reflectionsl = 98
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.022 w = 1/[σ2(Fo2) + (0.0115P)2 + 0.0246P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.055(Δ/σ)max < 0.001
S = 1.10Δρmax = 1.30 e Å3
721 reflectionsΔρmin = 1.11 e Å3
35 parametersExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.047 (6)
Crystal data top
CdC2O4V = 163.19 (3) Å3
Mr = 200.43Z = 2
Monoclinic, P21/nMo Kα radiation
a = 5.8260 (5) ŵ = 6.54 mm1
b = 5.2520 (7) ÅT = 293 K
c = 5.8320 (7) Å0.08 × 0.06 × 0.03 mm
β = 113.86 (2)°
Data collection top
Nonius KappaCCD area-detector
diffractometer
721 independent reflections
Absorption correction: integration
(Coppens, 1970)
557 reflections with I > 2σ(I)
Tmin = 0.615, Tmax = 0.841Rint = 0.025
1314 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02235 parameters
wR(F2) = 0.0550 restraints
S = 1.10Δρmax = 1.30 e Å3
721 reflectionsΔρmin = 1.11 e Å3
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 > 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 (Å2) top
xyzUiso*/Ueq
Cd0000.01316 (11)
O10.1107 (3)0.2305 (3)0.2625 (3)0.0161 (3)
O20.1786 (3)0.1954 (3)0.6104 (3)0.0149 (3)
C0.0832 (4)0.1218 (4)0.4619 (4)0.0122 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd0.01759 (16)0.01449 (16)0.00899 (16)0.00281 (7)0.00702 (11)0.00155 (7)
O10.0200 (8)0.0181 (8)0.0122 (7)0.0038 (6)0.0085 (6)0.0034 (6)
O20.0172 (8)0.0173 (8)0.0121 (7)0.0059 (6)0.0079 (6)0.0019 (6)
C0.0116 (9)0.0127 (10)0.0121 (10)0.0006 (9)0.0047 (7)0.0001 (8)
Geometric parameters (Å, º) top
Cd—O1i2.2417 (15)C—O11.246 (2)
Cd—O12.2417 (15)C—O21.264 (2)
Cd—O2ii2.3205 (15)O2—Cdvi2.3205 (15)
Cd—O2iii2.3205 (15)O2—Cdvii2.3461 (15)
Cd—O2iv2.3461 (15)C—Ciii1.557 (4)
Cd—O2v2.3461 (15)
O1i—Cd—O1180.00 (7)O1—Cd—O2v97.90 (6)
O1i—Cd—O2ii73.09 (5)O2ii—Cd—O2v92.34 (3)
O1—Cd—O2ii106.91 (5)O2iii—Cd—O2v87.66 (3)
O1i—Cd—O2iii106.91 (5)O2iv—Cd—O2v180.0
O1—Cd—O2iii73.09 (5)C—O1—Cd115.20 (14)
O2ii—Cd—O2iii180.0C—O2—Cdvi112.85 (13)
O1i—Cd—O2iv97.90 (6)C—O2—Cdvii122.94 (13)
O1—Cd—O2iv82.10 (6)Cdvi—O2—Cdvii124.21 (6)
O2ii—Cd—O2iv87.66 (3)O1—C—O2124.9 (2)
O2iii—Cd—O2iv92.34 (3)O1—C—Ciii118.2 (2)
O1i—Cd—O2v82.10 (6)O2—C—Ciii116.8 (2)
Symmetry codes: (i) x, y, z; (ii) x, y, z1; (iii) x, y, z+1; (iv) x+1/2, y+1/2, z1/2; (v) x1/2, y1/2, z+1/2; (vi) x, y, z+1; (vii) x1/2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaCdC2O4
Mr200.43
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)5.8260 (5), 5.2520 (7), 5.8320 (7)
β (°) 113.86 (2)
V3)163.19 (3)
Z2
Radiation typeMo Kα
µ (mm1)6.54
Crystal size (mm)0.08 × 0.06 × 0.03
Data collection
DiffractometerNonius KappaCCD area-detector
diffractometer
Absorption correctionIntegration
(Coppens, 1970)
Tmin, Tmax0.615, 0.841
No. of measured, independent and
observed [I > 2σ(I)] reflections
1314, 721, 557
Rint0.025
(sin θ/λ)max1)0.806
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.022, 0.055, 1.10
No. of reflections721
No. of parameters35
Δρmax, Δρmin (e Å3)1.30, 1.11

Computer programs: COLLECT (Nonius, 1998), SCALEPACK (Otwinowski & Minor, 1997), DENZO (Otwinowski & Minor, 1997) and SCALEPACK, SIR97 (Altomare et al., 1998), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 1999), SHELXL97.

Selected geometric parameters (Å, º) top
Cd—O12.2417 (15)C—O11.246 (2)
Cd—O2i2.3205 (15)C—O21.264 (2)
Cd—O2ii2.3461 (15)C—Ciii1.557 (4)
O1—C—O2124.9 (2)O2—C—Ciii116.8 (2)
O1—C—Ciii118.2 (2)
Symmetry codes: (i) x, y, z1; (ii) x1/2, y1/2, z+1/2; (iii) x, y, z+1.
 

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds