Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104006791/iz1040sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270104006791/iz1040Isup2.hkl |
CCDC reference: 243568
The Ba2Zr(C2O4)4·3H2O phase was synthesized by precipitation at the interface between an ethyl oxalate organic phase and an aqueous solution of barium chloride (BaCl2) and zirconyl chloride (ZrOCl2). Since diethyl oxalate is only very slightly soluble in water, it provides a slow release of oxalic acid at the interface between the organic and aqueous phases (Ryu et al., 1999). This procedure should give good control over the crystallization kinetics. The Ba:Zr ratio in the solution was varied between 1:1 and 2:1, with total cationic concentrations ranging between 0.125 M and 0.19 M. The mixtures were held for 2 d at different temperatures (279, 293 and 318 K). The white precipitates which formed were filtered and washed with water and acetone. All precipitates were characterized by powder X-ray diffraction (Siemens D-5000 diffractometer with Cu Kα radiation) and displayed similar diffraction patterns. Energy-dispersive analysis coupled to a scanning electron microscope (Philips XL-30 ESEM FEG) revealed a 2:1 Ba:Zr ratio in all samples, without a detectable secondary phase. From these results, it appears that the same phase is formed independently of the initial Ba:Zr ratio and of the crystallization temperature. In contrast, scanning electron microscopy shows that the morphology of the crystals depends on the crystallization temperature. At room temperature or below, elongated crystallites form `bundles' of crystals. At 318 K, larger tabular crystals were obtained, but intergrowth and twinning was frequently observed. The single-crystal of (I) used for the present structure determination was taken from the batch prepared at 318 K with a 1:1 Ba:Zr ratio.
Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Siemens, 1991); program(s) used to solve structure: SHELXTL; program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
[Ba2Zr(C2O4)4(H2O)3] | F(000) = 1432 |
Mr = 772.03 | Dx = 2.309 Mg m−3 |
Monoclinic, I2/a | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -I 2ya | Cell parameters from 35 reflections |
a = 9.2010 (12) Å | θ = 4.9–12.2° |
b = 29.032 (5) Å | µ = 4.05 mm−1 |
c = 9.2079 (17) Å | T = 293 K |
β = 115.45 (3)° | Prismatic, colourless |
V = 2221.0 (7) Å3 | 0.03 × 0.02 × 0.02 mm |
Z = 4 |
Bruker P4 diffractometer | 1510 reflections with I > 2σ(I) |
Radiation source: sealed tube | Rint = 0.060 |
Graphite monochromator | θmax = 25.0°, θmin = 2.0° |
2θ/ω scans | h = −10→9 |
Absorption correction: ψ scan (North et al., 1968) | k = −34→34 |
Tmin = 0.907, Tmax = 0.922 | l = −9→10 |
6582 measured reflections | 3 standard reflections every 97 reflections |
1964 independent reflections | intensity decay: none |
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)] = 0.047 | Hydrogen site location: undef |
wR(F2) = 0.124 | H-atom parameters not refined |
S = 1.05 | w = 1/[σ2(Fo2) + (0.038P)2 + 45.4129P] where P = (Fo2 + 2Fc2)/3 |
1964 reflections | (Δ/σ)max < 0.001 |
139 parameters | Δρmax = 2.05 e Å−3 |
0 restraints | Δρmin = −0.80 e Å−3 |
[Ba2Zr(C2O4)4(H2O)3] | V = 2221.0 (7) Å3 |
Mr = 772.03 | Z = 4 |
Monoclinic, I2/a | Mo Kα radiation |
a = 9.2010 (12) Å | µ = 4.05 mm−1 |
b = 29.032 (5) Å | T = 293 K |
c = 9.2079 (17) Å | 0.03 × 0.02 × 0.02 mm |
β = 115.45 (3)° |
Bruker P4 diffractometer | 1510 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.060 |
Tmin = 0.907, Tmax = 0.922 | 3 standard reflections every 97 reflections |
6582 measured reflections | intensity decay: none |
1964 independent reflections |
R[F2 > 2σ(F2)] = 0.047 | 0 restraints |
wR(F2) = 0.124 | H-atom parameters not refined |
S = 1.05 | w = 1/[σ2(Fo2) + (0.038P)2 + 45.4129P] where P = (Fo2 + 2Fc2)/3 |
1964 reflections | Δρmax = 2.05 e Å−3 |
139 parameters | Δρmin = −0.80 e Å−3 |
x | y | z | Uiso*/Ueq | ||
Ba1 | 0.2500 | 0.47133 (3) | 0.5000 | 0.0227 (3) | |
Ba2 | −0.2500 | 0.22910 (3) | 1.0000 | 0.0319 (3) | |
Zr1 | 0.2500 | 0.38452 (4) | 1.0000 | 0.0190 (3) | |
O1 | −0.1750 (8) | 0.4651 (3) | 0.7752 (9) | 0.0380 (18) | |
O2 | −0.0175 (9) | 0.4593 (3) | 0.5776 (8) | 0.0344 (17) | |
O3 | 0.1784 (8) | 0.4234 (2) | 0.7784 (8) | 0.0269 (15) | |
O4 | 0.0308 (8) | 0.4247 (3) | 0.9569 (8) | 0.0315 (16) | |
O5 | 0.1468 (8) | 0.3497 (2) | 1.1474 (8) | 0.0281 (15) | |
O6 | 0.0697 (9) | 0.3355 (3) | 0.8494 (8) | 0.0354 (18) | |
O7 | −0.1188 (10) | 0.2843 (3) | 0.8289 (9) | 0.0402 (19) | |
O8 | −0.0490 (14) | 0.3039 (4) | 1.1453 (11) | 0.074 (3) | |
O9W | −0.0259 (10) | 0.4438 (4) | 0.2333 (10) | 0.067 (3) | |
O10W | 0.2500 | 0.3756 (5) | 0.5000 | 0.079 (5) | |
C1 | −0.0473 (12) | 0.4455 (3) | 0.8221 (12) | 0.025 (2) | |
C2 | 0.0432 (12) | 0.4432 (3) | 0.7134 (12) | 0.024 (2) | |
C3 | 0.0273 (13) | 0.3227 (4) | 1.0819 (13) | 0.036 (3) | |
C4 | −0.0133 (13) | 0.3124 (4) | 0.9048 (13) | 0.033 (2) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ba1 | 0.0215 (4) | 0.0230 (5) | 0.0274 (5) | 0.000 | 0.0141 (3) | 0.000 |
Ba2 | 0.0445 (6) | 0.0239 (5) | 0.0304 (5) | 0.000 | 0.0190 (4) | 0.000 |
Zr1 | 0.0225 (7) | 0.0173 (7) | 0.0212 (6) | 0.000 | 0.0131 (5) | 0.000 |
O1 | 0.030 (4) | 0.048 (5) | 0.048 (4) | 0.012 (4) | 0.027 (3) | 0.011 (4) |
O2 | 0.037 (4) | 0.044 (5) | 0.034 (4) | 0.016 (4) | 0.026 (3) | 0.008 (3) |
O3 | 0.030 (4) | 0.030 (4) | 0.033 (4) | 0.010 (3) | 0.025 (3) | 0.013 (3) |
O4 | 0.026 (4) | 0.042 (5) | 0.028 (4) | 0.007 (3) | 0.013 (3) | 0.004 (3) |
O5 | 0.039 (4) | 0.019 (4) | 0.027 (4) | −0.008 (3) | 0.016 (3) | 0.000 (3) |
O6 | 0.039 (4) | 0.040 (5) | 0.033 (4) | −0.019 (3) | 0.021 (4) | −0.011 (3) |
O7 | 0.051 (5) | 0.043 (5) | 0.031 (4) | −0.013 (4) | 0.023 (4) | −0.005 (3) |
O8 | 0.100 (8) | 0.085 (8) | 0.054 (5) | −0.068 (7) | 0.048 (6) | −0.033 (5) |
O9W | 0.038 (5) | 0.116 (9) | 0.045 (5) | −0.008 (5) | 0.017 (4) | −0.042 (5) |
O10W | 0.122 (13) | 0.034 (8) | 0.075 (9) | 0.000 | 0.036 (9) | 0.000 |
C1 | 0.033 (6) | 0.019 (5) | 0.036 (6) | −0.001 (4) | 0.026 (5) | 0.005 (4) |
C2 | 0.028 (5) | 0.015 (5) | 0.037 (6) | 0.000 (4) | 0.021 (5) | 0.002 (4) |
C3 | 0.039 (6) | 0.037 (6) | 0.032 (6) | −0.015 (6) | 0.014 (5) | 0.000 (5) |
C4 | 0.037 (6) | 0.026 (6) | 0.034 (6) | −0.008 (5) | 0.013 (5) | 0.004 (5) |
Ba1—O10W | 2.778 (14) | Zr1—O5 | 2.209 (6) |
Ba1—O9W | 2.785 (8) | Zr1—O4viii | 2.213 (7) |
Ba1—O9Wi | 2.785 (8) | Zr1—O4 | 2.213 (7) |
Ba1—O2ii | 2.799 (7) | O1—C1 | 1.205 (12) |
Ba1—O2iii | 2.799 (7) | O1—O9Wix | 2.789 (11) |
Ba1—O2i | 2.864 (7) | O1—Ba1iii | 2.968 (7) |
Ba1—O2 | 2.864 (7) | O2—C2 | 1.222 (12) |
Ba1—O1ii | 2.968 (7) | O2—Ba1iii | 2.799 (7) |
Ba1—O1iii | 2.968 (7) | O3—C2 | 1.263 (11) |
Ba1—O3i | 3.224 (6) | O4—C1 | 1.287 (12) |
Ba1—O3 | 3.224 (6) | O4—O9Wx | 2.863 (11) |
Ba1—C2i | 3.370 (9) | O5—C3 | 1.272 (12) |
Ba2—O7iv | 2.764 (7) | O5—O10Wx | 3.059 (7) |
Ba2—O7v | 2.764 (7) | O6—C4 | 1.277 (12) |
Ba2—O8 | 2.793 (9) | O7—C4 | 1.230 (13) |
Ba2—O8vi | 2.793 (9) | O7—Ba2iv | 2.764 (7) |
Ba2—O7 | 2.854 (8) | O8—C3 | 1.218 (14) |
Ba2—O7vi | 2.854 (8) | O9W—O1ix | 2.789 (11) |
Ba2—Ba2iv | 4.7612 (9) | O9W—O4xi | 2.863 (11) |
Ba2—Ba2vii | 4.7612 (10) | O9W—O10W | 3.321 (14) |
Zr1—O3viii | 2.172 (6) | O10W—O5xi | 3.059 (7) |
Zr1—O3 | 2.172 (6) | O10W—O5viii | 3.059 (7) |
Zr1—O6 | 2.173 (7) | O10W—O9Wi | 3.321 (14) |
Zr1—O6viii | 2.173 (7) | C1—C2 | 1.555 (13) |
Zr1—O5viii | 2.209 (6) | C3—C4 | 1.537 (15) |
O10W—Ba1—O9W | 73.3 (2) | O7—Ba2—Ba2iv | 31.49 (15) |
O10W—Ba1—O9Wi | 73.3 (2) | O7vi—Ba2—Ba2iv | 124.49 (15) |
O9W—Ba1—O9Wi | 146.6 (5) | O7iv—Ba2—Ba2vii | 156.08 (18) |
O10W—Ba1—O2ii | 136.04 (16) | O7v—Ba2—Ba2vii | 32.64 (16) |
O9W—Ba1—O2ii | 137.6 (3) | O8—Ba2—Ba2vii | 67.27 (18) |
O9Wi—Ba1—O2ii | 71.0 (3) | O8vi—Ba2—Ba2vii | 89.42 (19) |
O10W—Ba1—O2iii | 136.04 (16) | O7—Ba2—Ba2vii | 124.49 (15) |
O9W—Ba1—O2iii | 71.0 (3) | O7vi—Ba2—Ba2vii | 31.49 (15) |
O9Wi—Ba1—O2iii | 137.6 (3) | Ba2iv—Ba2—Ba2vii | 150.47 (4) |
O2ii—Ba1—O2iii | 87.9 (3) | O3viii—Zr1—O3 | 117.4 (4) |
O10W—Ba1—O2i | 82.98 (16) | O3viii—Zr1—O6 | 141.3 (2) |
O9W—Ba1—O2i | 107.5 (2) | O3—Zr1—O6 | 84.3 (3) |
O9Wi—Ba1—O2i | 68.3 (2) | O3viii—Zr1—O6viii | 84.3 (3) |
O2ii—Ba1—O2i | 60.5 (3) | O3—Zr1—O6viii | 141.3 (2) |
O2iii—Ba1—O2i | 131.98 (18) | O6—Zr1—O6viii | 98.2 (4) |
O10W—Ba1—O2 | 82.98 (16) | O3viii—Zr1—O5viii | 141.1 (3) |
O9W—Ba1—O2 | 68.3 (2) | O3—Zr1—O5viii | 72.4 (2) |
O9Wi—Ba1—O2 | 107.5 (2) | O6—Zr1—O5viii | 73.7 (3) |
O2ii—Ba1—O2 | 131.98 (18) | O6viii—Zr1—O5viii | 71.4 (2) |
O2iii—Ba1—O2 | 60.5 (3) | O3viii—Zr1—O5 | 72.4 (2) |
O2i—Ba1—O2 | 166.0 (3) | O3—Zr1—O5 | 141.1 (3) |
O10W—Ba1—O1ii | 128.49 (16) | O6—Zr1—O5 | 71.4 (2) |
O9W—Ba1—O1ii | 136.2 (2) | O6viii—Zr1—O5 | 73.7 (3) |
O9Wi—Ba1—O1ii | 68.7 (3) | O5viii—Zr1—O5 | 125.4 (4) |
O2ii—Ba1—O1ii | 57.46 (19) | O3viii—Zr1—O4viii | 70.9 (2) |
O2iii—Ba1—O1ii | 69.0 (2) | O3—Zr1—O4viii | 77.3 (3) |
O2i—Ba1—O1ii | 112.30 (19) | O6—Zr1—O4viii | 147.8 (3) |
O2—Ba1—O1ii | 76.9 (2) | O6viii—Zr1—O4viii | 81.0 (3) |
O10W—Ba1—O1iii | 128.49 (16) | O5viii—Zr1—O4viii | 75.6 (3) |
O9W—Ba1—O1iii | 68.7 (3) | O5—Zr1—O4viii | 137.0 (2) |
O9Wi—Ba1—O1iii | 136.2 (2) | O3viii—Zr1—O4 | 77.3 (3) |
O2ii—Ba1—O1iii | 69.0 (2) | O3—Zr1—O4 | 70.9 (2) |
O2iii—Ba1—O1iii | 57.46 (19) | O6—Zr1—O4 | 81.0 (3) |
O2i—Ba1—O1iii | 76.9 (2) | O6viii—Zr1—O4 | 147.8 (3) |
O2—Ba1—O1iii | 112.30 (19) | O5viii—Zr1—O4 | 137.0 (2) |
O1ii—Ba1—O1iii | 103.0 (3) | O5—Zr1—O4 | 75.6 (3) |
O10W—Ba1—O3i | 64.43 (12) | O4viii—Zr1—O4 | 116.4 (4) |
O9W—Ba1—O3i | 66.1 (2) | C1—O1—O9Wix | 134.8 (7) |
O9Wi—Ba1—O3i | 99.0 (3) | C1—O1—Ba1iii | 115.6 (6) |
O2ii—Ba1—O3i | 96.82 (18) | O9Wix—O1—Ba1iii | 104.4 (3) |
O2iii—Ba1—O3i | 120.18 (19) | C2—O2—Ba1iii | 120.0 (6) |
O2i—Ba1—O3i | 42.07 (18) | C2—O2—Ba1 | 103.8 (6) |
O2—Ba1—O3i | 129.56 (19) | Ba1iii—O2—Ba1 | 119.5 (3) |
O1ii—Ba1—O3i | 153.59 (17) | C2—O3—Zr1 | 121.4 (6) |
O1iii—Ba1—O3i | 69.01 (19) | C2—O3—Ba1 | 85.6 (5) |
O10W—Ba1—O3 | 64.43 (12) | Zr1—O3—Ba1 | 152.7 (3) |
O9W—Ba1—O3 | 99.0 (3) | C1—O4—Zr1 | 120.6 (6) |
O9Wi—Ba1—O3 | 66.1 (2) | C1—O4—O9Wx | 121.8 (6) |
O2ii—Ba1—O3 | 120.18 (19) | Zr1—O4—O9Wx | 116.3 (3) |
O2iii—Ba1—O3 | 96.82 (18) | C3—O5—Zr1 | 120.2 (6) |
O2i—Ba1—O3 | 129.56 (19) | C3—O5—O10Wx | 117.8 (6) |
O2—Ba1—O3 | 42.07 (18) | Zr1—O5—O10Wx | 121.3 (3) |
O1ii—Ba1—O3 | 69.01 (19) | C4—O6—Zr1 | 120.9 (6) |
O1iii—Ba1—O3 | 153.59 (17) | C4—O7—Ba2iv | 125.6 (7) |
O3i—Ba1—O3 | 128.9 (2) | C4—O7—Ba2 | 118.5 (6) |
O10W—Ba1—C2i | 75.97 (16) | Ba2iv—O7—Ba2 | 115.9 (3) |
O9W—Ba1—C2i | 86.9 (2) | C3—O8—Ba2 | 121.2 (8) |
O9Wi—Ba1—C2i | 85.1 (3) | Ba1—O9W—O1ix | 118.4 (3) |
O2ii—Ba1—C2i | 76.2 (2) | Ba1—O9W—O4xi | 113.2 (3) |
O2iii—Ba1—C2i | 125.9 (2) | O1ix—O9W—O4xi | 124.9 (4) |
O2i—Ba1—C2i | 20.6 (2) | Ba1—O9W—O10W | 53.3 (3) |
O2—Ba1—C2i | 151.3 (2) | O1ix—O9W—O10W | 125.8 (4) |
O1ii—Ba1—C2i | 131.8 (2) | O4xi—O9W—O10W | 99.7 (3) |
O1iii—Ba1—C2i | 68.6 (2) | Ba1—O10W—O5xi | 104.3 (3) |
O3i—Ba1—C2i | 21.9 (2) | Ba1—O10W—O5viii | 104.3 (3) |
O3—Ba1—C2i | 135.9 (2) | O5xi—O10W—O5viii | 151.5 (6) |
O7iv—Ba2—O7v | 163.8 (3) | Ba1—O10W—O9Wi | 53.4 (3) |
O7iv—Ba2—O8 | 121.5 (3) | O5xi—O10W—O9Wi | 136.2 (3) |
O7v—Ba2—O8 | 72.4 (3) | O5viii—O10W—O9Wi | 64.7 (2) |
O7iv—Ba2—O8vi | 72.4 (3) | O1—C1—O4 | 128.4 (9) |
O7v—Ba2—O8vi | 121.5 (3) | O1—C1—C2 | 119.9 (9) |
O8—Ba2—O8vi | 77.9 (5) | O4—C1—C2 | 111.7 (8) |
O7iv—Ba2—O7 | 64.1 (3) | O2—C2—O3 | 125.7 (9) |
O7v—Ba2—O7 | 126.5 (3) | O2—C2—C1 | 120.4 (9) |
O8—Ba2—O7 | 58.5 (2) | O3—C2—C1 | 113.9 (8) |
O8vi—Ba2—O7 | 69.4 (3) | O2—C2—Ba1 | 55.6 (5) |
O7iv—Ba2—O7vi | 126.5 (3) | O3—C2—Ba1 | 72.5 (5) |
O7v—Ba2—O7vi | 64.1 (3) | C1—C2—Ba1 | 163.3 (6) |
O8—Ba2—O7vi | 69.4 (3) | O8—C3—O5 | 127.4 (10) |
O8vi—Ba2—O7vi | 58.5 (2) | O8—C3—C4 | 119.7 (10) |
O7—Ba2—O7vi | 111.6 (3) | O5—C3—C4 | 112.9 (9) |
O7iv—Ba2—Ba2iv | 32.64 (16) | O7—C4—O6 | 125.7 (10) |
O7v—Ba2—Ba2iv | 156.08 (18) | O7—C4—C3 | 120.2 (9) |
O8—Ba2—Ba2iv | 89.42 (19) | O6—C4—C3 | 114.1 (9) |
O8vi—Ba2—Ba2iv | 67.27 (18) |
Symmetry codes: (i) −x+1/2, y, −z+1; (ii) x+1/2, −y+1, z; (iii) −x, −y+1, −z+1; (iv) −x−1/2, −y+1/2, −z+3/2; (v) x, −y+1/2, z+1/2; (vi) −x−1/2, y, −z+2; (vii) −x−1/2, −y+1/2, −z+5/2; (viii) −x+1/2, y, −z+2; (ix) −x−1/2, y, −z+1; (x) x, y, z+1; (xi) x, y, z−1. |
Experimental details
Crystal data | |
Chemical formula | [Ba2Zr(C2O4)4(H2O)3] |
Mr | 772.03 |
Crystal system, space group | Monoclinic, I2/a |
Temperature (K) | 293 |
a, b, c (Å) | 9.2010 (12), 29.032 (5), 9.2079 (17) |
β (°) | 115.45 (3) |
V (Å3) | 2221.0 (7) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 4.05 |
Crystal size (mm) | 0.03 × 0.02 × 0.02 |
Data collection | |
Diffractometer | Bruker P4 diffractometer |
Absorption correction | ψ scan (North et al., 1968) |
Tmin, Tmax | 0.907, 0.922 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6582, 1964, 1510 |
Rint | 0.060 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.047, 0.124, 1.05 |
No. of reflections | 1964 |
No. of parameters | 139 |
H-atom treatment | H-atom parameters not refined |
w = 1/[σ2(Fo2) + (0.038P)2 + 45.4129P] where P = (Fo2 + 2Fc2)/3 | |
Δρmax, Δρmin (e Å−3) | 2.05, −0.80 |
Computer programs: XSCANS (Siemens, 1996), XSCANS, SHELXTL (Siemens, 1991), SHELXTL.
Ba1—O10W | 2.778 (14) | Ba2—O7 | 2.854 (8) |
Ba1—O9W | 2.785 (8) | Zr1—O3 | 2.172 (6) |
Ba1—O2i | 2.799 (7) | Zr1—O6 | 2.173 (7) |
Ba1—O2 | 2.864 (7) | Zr1—O5 | 2.209 (6) |
Ba1—O1i | 2.968 (7) | Zr1—O4 | 2.213 (7) |
Ba1—O3 | 3.224 (6) | O9W—O1iii | 2.789 (11) |
Ba2—O7ii | 2.764 (7) | O9W—O4iv | 2.863 (11) |
Ba2—O8 | 2.793 (9) | O10W—O5iv | 3.059 (7) |
Symmetry codes: (i) x+1/2, −y+1, z; (ii) −x−1/2, −y+1/2, −z+3/2; (iii) −x−1/2, y, −z+1; (iv) x, y, z−1. |
Oxalate complexes can be used as precursors in the formation of ternary oxides. For example, the barium titanate perovskite BaTiO3 can be synthesized by thermal decomposition of the mixed oxalate BaTiO(C2O4)2·4H2O (Wada et al., 2003). Due to the great interest in the dielectric and ferroelectric properties of BaTiO3, the crystallographic structure of barium titanyl oxalate is well documented (Rhine et al., 1992). In contrast, very little work has been done in the case of the barium zirconium oxalate, even though it might be a precursor for the formation of barium zirconate. BaZrO3 has potential interest as a refractory material, due to its ability to resist the corrosive fluxes encountered during the synthesis of copper-based superconducting phases (Erb et al., 1995). The manufacture of BaZrO3 crucibles requires a very good densification behaviour, influenced by the morphology and size distribution of the particles (Robertz et al., 2001). Therefore, the determination of the crystallographic structure of the title compound, (I), a potential precursor, is of some interest. \sch
The unindexed powder diffraction pattern published by Reddy & Mehrotra (1997) is attributed to a BaZrO(C2O4)2·4.5H2O phase. In the present study, the structural refinement of single-crystal data indicates a Ba2Zr(C2O4)4·3H2O composition. The Ba:Zr ratio is confirmed by energy-dispersive spectrometry. A similar composition was found by other authors, in the case of the lead zirconium oxalate Pb2Zr(C2O4)4.nH2O (Boudaren et al., 2000) and for Cd2Zr(C2O4)4·4H2O (Jeanneau et al., 2001).
The complex three-dimensional structure of (I) is built from Zr and Ba atoms linked by oxalate groups (Fig. 1). The coordination polyhedra have imposed C2 symmetry, the Zr and Ba atoms lying on crystallographic twofold axes. The Zr atom is eightfold coordinated by O atoms from bridging bidentate oxalate groups. There are two symmetrically non-equivalent Ba atoms per asymmetric unit. One Ba atom, Ba1, is surrounded by eight O atoms from four bidendate oxalate ligands (two symmetrically non-equivalent). Atom Ba1 is also linked to three water O atoms (from two symmetry-distinct water molecules), reaching a coordination number of 11. The second Ba atom is sixfold coordinated to four O atoms, which belong to two (symmetrically equivalent) bidendate and to two (symmetrically equivalent) monodendate oxalate anions, respectively.
Intermolecular contacts (Table 1) indicate probable hydrogen bonding between water and oxalate O atoms. Fig. 2 shows how the metal atoms alternate in the crystal packing of (I).