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Acta Crystallogr Sect E Struct Rep Online. 2008 August 1; 64(Pt 8): m983.
Published online 2008 July 5. doi:  10.1107/S1600536808019508
PMCID: PMC2961912

Poly[disodium [diaqua­tri-μ2-oxalato-dimagnesium(II)]]

Abstract

The title compound, {Na2[Mg2(C2O4)3(H2O)2]}n, is isotypic with its Co analogue. There are two crystallographically independent oxalate groups in the asymmetric unit, one lying on an inversion center and the other on a general position. Mg2+ ions are ligated by H2O mol­ecules and bridged by tri- and tetra­dentate oxalate ligands, forming ladder-like double chains that are held together via O—H(...)O hydrogen bonds, with Na+ cations located between the chains to balance the charge.

Related literature

For related literature, see: Audebrand et al. (2003 [triangle]); Brown & Altermatt (1985 [triangle]); Dean et al. (2004 [triangle]); Kolitsch (2004 [triangle]); Lethbridge et al. (2003 [triangle]); Lu et al. (2004 [triangle]); Miessen & Hoppe (1987 [triangle]); Price et al. (2000 [triangle]); Schefer & Grube (1995 [triangle]); Shannon (1976 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-64-0m983-scheme1.jpg

Experimental

Crystal data

  • Na2[Mg2(C2O4)3(H2O)2]
  • M r = 394.70
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-64-0m983-efi1.jpg
  • a = 5.8460 (12) Å
  • b = 15.726 (3) Å
  • c = 7.0190 (14) Å
  • β = 101.11 (3)°
  • V = 633.2 (2) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 0.34 mm−1
  • T = 290 K
  • 0.4 × 0.2 × 0.2 mm

Data collection

  • Rigaku AFC-7R diffractometer
  • Absorption correction: ψ scan (Kopfmann & Huber, 1968 [triangle]) T min = 0.912, T max = 0.943
  • 2457 measured reflections
  • 2280 independent reflections
  • 2027 reflections with I > 2σ(I)
  • R int = 0.029
  • 3 standard reflections every 150 reflections intensity decay: 1.2%

Refinement

  • R[F 2 > 2σ(F 2)] = 0.033
  • wR(F 2) = 0.095
  • S = 1.11
  • 2280 reflections
  • 118 parameters
  • All H-atom parameters refined
  • Δρmax = 0.54 e Å−3
  • Δρmin = −0.56 e Å−3

Data collection: AFC Diffractometer Control Software (Rigaku, 1994 [triangle]); cell refinement: AFC Diffractometer Control Software; data reduction: AFC Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: ATOMS (Dowty, 1999 [triangle]); software used to prepare material for publication: SHELXL97.

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808019508/bq2084sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808019508/bq2084Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This work was supported by the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality.

supplementary crystallographic information

Comment

Oxalates are of considerable interest because many of them are natural minerals and in addition, the oxalate anion can adopt different coordination modes to bind metals to form infinite chains, sheets and networks, leading to the rich structural chemistry (Lu et al., 2004; Dean et al., 2004; Audebrand et al., 2003). In the system of mixed oxalates, AxBy(C2O4)z.nH2O, combining alkali-metal elements (A) and alkali-earth-metal cations (B), only one compound, Cs2Mg(C2O4)2.4H2O, has been previously found, and it has a layered structure character in which layers of MgO4(H2O)2 octahedra paralel to (10–1) are separated by corrugated layers of nine-coordinated Cs atoms (Kolitsch, 2004). During our exploratory syntheses of novel hydrated borate materials, we have obtained a new member of the AxBy(C2O4)z.nH2O family of compounds, Na2Mg2(C2O4)3.2H2O. It has a one-dimensional character consisting of [Mg2(C2O4)3(H2O)2]n2n- infinite chains. We describe its synthesis and crystal structure here for the first time.

The title compound is isotypic with its Co analogue (Price et al., 2000) and the crystal structure consists of Na+ and Mg2+ cations, [C2O4]2- groups, and H2O molecules as the fundamental structural building units (Fig. 1). Mg2+ ions are ligated by H2O molecules and bridged by tri-dentate oxalate ligands to generate a one-dimensional infinite polymeric chain, [Mg(C2O4)(H2O)]n. Two neighboring inversion-center-related [Mg(C2O4)(H2O)]n chains are further bridged by tetra-dentate oxalate ligands to complete the octahedral coordination sphere of Mg2+ and to form a ladder-like double chain with the composition [Mg2(C2O4)3(H2O)2]n2n- (Fig. 2 b). Mg···Mg distances along the double chain are 5.846 (1) Å, slightly longer than those across the chain (5.390 (1) Å). The [Mg2(C2O4)3(H2O)2]n2n- chains extend along the [100] direction and pack in two orientations in a herringbone pattern, as illustrated in Fig.2a. These chains are held together via medium-to-weak O—H···O hydrogen bonds existing between the coordinated H2O molecules and the O atoms from tri-dentate oxalate ligands (Table 1). Na+ cations are located in the void space between the chains to balance charge.

There is one crystallographically independent Na+ cation, which is coordinated to seven O atoms, forming an irregular coordination polyhedral geometry. The Na—O distances range from 2.2952 (10) to 2.8074 (10) Å, with an average of 2.510 Å, which is comparable to the value 2.46 Å computed from crystal radii for a 7-coordinated Na+ ion (Shannon, 1976) and the distances 2.409 (3)–2.606 (3) Å (average 2.505 Å, CN = 7) in NaLi2BO3 (Miessen & Hoppe, 1987). Bond valence sum (BVS) calculations using Brown's formula (Brown & Altermatt,1985) produced a BVS value of 1.15 for Na, in good agreement with its expected formal valence. The Mg atom also occupies one crystallographically distinct site. However, each Mg2+ is coordinated by six O atoms, five of which are from three oxalate ions and the other from one H2O molecule. The MgO6 octahedron is strongly distorted, with the 180° octahedral angles being 162.33 (4)–171.66 (3)°, and the 90° octahedral angles in the range 78.40 (3)–99.05 (4)°, the smallest angle being associated with the constrained Mg1—O4i—C2i –C3i –O5i five-membered ring [Symmetry codes: (i) -1 + x, y, z]. The Mg—O distances of 2.0436 (9)–2.1429 (9) Å (average 2.078 Å) are very reasonable when compared with the ranges 2.057 (9)–2.080 (9) Å (average 2.065 Å) in Mg(NO3)2.6H2O, where octahedrally coordinated Mg2+ is also found (Schefer & Grube, 1995). The calculated BVS value for Mg is also reasonable, at 2.12. Of the two unique oxalate ions, the C1-based oxalate sits on an inversion center and the C2/C3-based one on a general position. Both oxalate ions are nearly planar, with a mean deviation of 0.0004 and 0.1418 Å, respectively, and the bond geometries of [C2O4]2- are in accord with those observed in other oxalate compounds (Lethbridge et al., 2003).

Experimental

The title compound was synthesized by a two-step process. First, for the preparation of the precursor, Na3MgB5O10, a stoichiometric mixture of Na2CO3, MgO, and H3BO3 was heated at 873 K for two weeks with several intermediate re-mixings and the resulting product was identified to be the pure phase of Na3MgB5O10 based on the powder XRD analysis. Then, a 0.300 g (0.976 mmol) sample of Na3MgB5O10, 0.300 g (2.380 mmol) H2(C2O4).2H2O, and 3 ml H2O were sealed in an 15-ml Teflon-lined autoclave and subsequently heated at 453 K for one week, then cooled slowly to room temperature. The product consisted of colorless, prismatic crystals with the largest having dimensions of 0.6 × 0.6 × 1.2 mm3 in colorless mother liquor. The final pH of the reaction system was about 2.0. The crystals were isolated in about 70% yield (based on Mg) by washing the reaction product with deionized water and anhydrous ethanol followed by drying with anhydrous acetone. The powder XRD pattern of the ground crystals is in good agreement with that calculated from the single-crystal data, confirming that the pure phase of the title compound has been obtained. Although boron was not incorporated into the final structure, borate anions may serve as mineralizers to enhance the crystal growth.

Refinement

H-atom positions were located in a difference Fourier map and all associated parameters were refined freely.

Figures

Fig. 1.
The connectivity in Na2Mg2(C2O4)3.2H2O, shown with displacement ellipsoids at the 50% probability level. [Symmetry codes: (i) -1 + x, y, z; (iv) 1 - x, 1 - y, 1 - z]
Fig. 2.
The crystal structure of Na2Mg2(C2O4)3.2H2O projected along the [100] direction (a) as well as the single chain of [Mg2(C2O4)3(H2O)2]n2n- (b). H···O hydrogen bond contacts are shown as dashed lines; symmetry codes are the same ...

Crystal data

Na2[Mg2(C2O4)3(H2O)2]F(000) = 396
Mr = 394.70Dx = 2.070 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 25 reflections
a = 5.8460 (12) Åθ = 21.9–22.5°
b = 15.726 (3) ŵ = 0.34 mm1
c = 7.0190 (14) ÅT = 290 K
β = 101.11 (3)°Prism, colorless
V = 633.2 (2) Å30.4 × 0.2 × 0.2 mm
Z = 2

Data collection

Rigaku AFC-7R diffractometer2027 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.029
graphiteθmax = 32.5°, θmin = 2.6°
2θ–ω scansh = 0→8
Absorption correction: ψ scan (Kopfmann & Huber, 1968)k = 0→23
Tmin = 0.912, Tmax = 0.943l = −10→10
2457 measured reflections3 standard reflections every 150 reflections
2280 independent reflections intensity decay: 1.2%

Refinement

Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033All H-atom parameters refined
wR(F2) = 0.095w = 1/[σ2(Fo2) + (0.0581P)2 + 0.0731P] where P = (Fo2 + 2Fc2)/3
S = 1.11(Δ/σ)max = 0.001
2280 reflectionsΔρmax = 0.54 e Å3
118 parametersΔρmin = −0.56 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.310 (14)

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 (Å2)

xyzUiso*/Ueq
Na10.46789 (7)0.81852 (3)0.30526 (7)0.01952 (13)
Mg10.27308 (6)0.60144 (2)0.21580 (5)0.01297 (12)
C10.49584 (17)0.46394 (6)0.42523 (14)0.01492 (18)
O10.38596 (15)0.47765 (5)0.25634 (11)0.01885 (17)
O20.60143 (15)0.39673 (5)0.48571 (11)0.02059 (18)
C20.79984 (15)0.64930 (6)0.21459 (13)0.01346 (18)
O30.58217 (13)0.65770 (5)0.17720 (13)0.02067 (17)
O40.91349 (13)0.58130 (5)0.22737 (12)0.01867 (17)
C30.94672 (16)0.73184 (6)0.24642 (14)0.01425 (18)
O51.15751 (12)0.72335 (5)0.23254 (12)0.01735 (17)
O60.85117 (14)0.79871 (5)0.28409 (15)0.0255 (2)
O70.18307 (14)0.58554 (5)−0.08136 (12)0.01742 (16)
H7A0.174 (4)0.5388 (16)−0.124 (4)0.058 (7)*
H7B0.065 (5)0.6120 (18)−0.141 (4)0.077 (9)*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Na10.0152 (2)0.0208 (2)0.0230 (2)−0.00005 (15)0.00461 (16)0.00233 (16)
Mg10.01111 (17)0.01020 (17)0.01744 (18)0.00096 (10)0.00233 (12)0.00035 (10)
C10.0171 (4)0.0111 (4)0.0166 (4)0.0015 (3)0.0031 (3)−0.0012 (3)
O10.0258 (4)0.0130 (3)0.0161 (3)0.0031 (3)−0.0001 (3)−0.0011 (2)
O20.0289 (4)0.0134 (3)0.0179 (3)0.0080 (3)0.0005 (3)−0.0014 (2)
C20.0104 (4)0.0140 (4)0.0165 (4)−0.0015 (3)0.0039 (3)−0.0008 (3)
O30.0100 (3)0.0223 (4)0.0300 (4)−0.0018 (3)0.0045 (3)0.0009 (3)
O40.0147 (3)0.0120 (3)0.0297 (4)−0.0007 (2)0.0054 (3)−0.0008 (3)
C30.0105 (4)0.0120 (4)0.0200 (4)0.0002 (3)0.0022 (3)−0.0009 (3)
O50.0102 (3)0.0113 (3)0.0310 (4)0.0000 (2)0.0051 (3)−0.0008 (3)
O60.0150 (3)0.0144 (3)0.0470 (5)0.0026 (3)0.0062 (3)−0.0083 (3)
O70.0176 (3)0.0148 (3)0.0191 (3)0.0019 (3)0.0017 (3)−0.0011 (2)

Geometric parameters (Å, °)

Na1—O62.2952 (10)Mg1—O4i2.1429 (9)
Na1—O5i2.3315 (9)C1—O11.2533 (12)
Na1—O2ii2.3514 (10)C1—O21.2559 (11)
Na1—O7iii2.4886 (10)C1—C1iv1.5399 (19)
Na1—O3iii2.5941 (12)C2—O41.2531 (12)
Na1—O1ii2.7059 (10)C2—O31.2557 (11)
Na1—O32.8074 (10)C2—C31.5485 (13)
Mg1—O5i2.0436 (9)C3—O61.2428 (12)
Mg1—O12.058 (1)C3—O51.2618 (11)
Mg1—O72.0656 (10)O7—H7A0.79 (3)
Mg1—O32.0761 (9)O7—H7B0.85 (3)
Mg1—O2iv2.0823 (10)
O6—Na1—O5i128.83 (4)O5i—Mg1—O2iv89.17 (3)
O6—Na1—O2ii91.25 (4)O1—Mg1—O2iv80.36 (3)
O5i—Na1—O2ii98.57 (4)O7—Mg1—O2iv171.66 (3)
O6—Na1—O7iii145.56 (3)O3—Mg1—O2iv88.78 (5)
O5i—Na1—O7iii85.34 (3)O5i—Mg1—O4i78.40 (3)
O2ii—Na1—O7iii86.94 (4)O1—Mg1—O4i98.38 (4)
O6—Na1—O3iii91.11 (4)O7—Mg1—O4i87.68 (5)
O5i—Na1—O3iii110.58 (4)O3—Mg1—O4i162.33 (4)
O2ii—Na1—O3iii140.04 (3)O2iv—Mg1—O4i97.00 (5)
O7iii—Na1—O3iii69.46 (3)O1—C1—O2126.40 (9)
O6—Na1—O1ii76.88 (3)O1—C1—C1iv117.46 (10)
O5i—Na1—O1ii144.59 (3)O2—C1—C1iv116.14 (11)
O2ii—Na1—O1ii52.00 (3)C1—O1—Mg1112.70 (6)
O7iii—Na1—O1ii75.03 (3)C1—O2—Mg1iv112.55 (6)
O3iii—Na1—O1ii89.97 (3)O4—C2—O3127.35 (9)
O6—Na1—O363.99 (3)O4—C2—C3115.69 (8)
O5i—Na1—O364.84 (3)O3—C2—C3116.96 (8)
O2ii—Na1—O3101.83 (3)C2—O3—Mg1143.16 (7)
O7iii—Na1—O3149.74 (3)C2—O4—Mg1v112.43 (6)
O3iii—Na1—O3114.90 (3)O6—C3—O5126.27 (9)
O1ii—Na1—O3132.84 (3)O6—C3—C2118.71 (8)
O5i—Mg1—O1168.63 (4)O5—C3—C2115.01 (8)
O5i—Mg1—O798.56 (4)C3—O5—Mg1v116.25 (6)
O1—Mg1—O792.16 (3)Mg1—O7—H7A118.6 (19)
O5i—Mg1—O385.03 (3)Mg1—O7—H7B117.6 (19)
O1—Mg1—O399.05 (4)H7A—O7—H7B106 (2)
O7—Mg1—O388.77 (4)

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

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O7—H7a···O4vi0.78 (3)2.06 (3)2.8335 (13)170 (2)
O7—H7b···O6vii0.84 (3)1.89 (3)2.6952 (13)162 (3)

Symmetry codes: (vi) −x+1, −y+1, −z; (vii) x−1, −y+3/2, z−1/2.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BQ2084).

References

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