Synthesis and characterization of the barium oxalates BaC₂O₄·0.5H₂O, α-BaC₂O₄ and β-BaC₂O₄

The synthesis of BaC₂O₄·0.5H₂O and its thermal decomposition to α-BaC₂O₄ and β-BaC₂O₄ was investigated. BaC₂O₄·0.5H₂O is precipitated at room temperature from aqueous solutions of barium chloride and ammonium oxalate. The deuterated compound BaC₂O₄·0.5D₂O was made in analogy with D₂O as the solvent. The compounds were characterized by X-ray and neutron diffraction analysis. Single-crystal X-ray diffraction of BaC₂O₄·0.5H₂O measured at 120 K gave the triclinic cell a = 8.692 (1), b = 9.216 (1), c = 6.146 (1) Å, α = 95.094 (3), β = 95.492 (3), γ = 64.500 (3)°, space group P, Z = 4. Two independent Ba atoms are each coordinated to nine O atoms at distances from 2.73 (1) to 2.99 (1) Å. One of the two oxalate ions deviates significantly from planarity. The water molecule does form weak hydrogen bonds. In situ X-ray powder diffraction was used to study the thermal decomposition of BaC₂O₄·0.5H₂O and the formation of α-BaC₂O₄. The X-ray powder pattern of α-BaC₂O₄ measured at 473 K was indexed on a triclinic cell with a = 5.137 (3), b = 8.764 (6), c = 9.006 (4) Å, α = 83.57 (4), β = 98.68 (5), γ = 99.53 (5)°, and the space group P with Z = 4.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SIR97 (Altomare et al., 1997 ), KRYSTAL; program(s) used to refine structure: modified ORFLS(1962), KRYSTAL; molecular graphics: ORTEP-III (Burnett & Johnson, 1996), KRYSTAL; software used to prepare material for publication: KRYSTAL.

Figures

(baox05)

Crystal data

C4H2Ba2O9	Z = 2
Mr = 468.72	F(000) = 420
Triclinic, P1	Dx = 3.524 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 8.692 (1) Å	Cell parameters from 1438 reflections
b = 9.216 (1) Å	θ = 2.5–30.5°
c = 6.146 (1) Å	µ = 8.89 mm^−1
α = 95.094 (3)°	T = 120 K
β = 95.492 (3)°	Plate, colourless
γ = 64.500 (3)°	0.15 × 0.06 × 0.01 mm
V = 441.7 (1) Å^3

Data collection

Siemens SMART CCD diffractometer	2584 independent reflections
Radiation source: x-ray tube	1339 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.075
ω rotation scans with narrow frames	θmax = 30.5°, θmin = 2.5°
Absorption correction: integration XPREP,1995	h = −12→12
Tmin = 0.28, Tmax = 0.84	k = −13→13
12950 measured reflections	l = −8→8

Refinement

Refinement on F	0 constraints
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.050	w = 1/{[σcs(F^2) + 1.03F^2]^1/2- |F|}^2
wR(F^2) = 0.054	(Δ/σ)max = 0.00013
S = 1.20	Δρmax = 4.0 (5) e Å^−3
1339 reflections	Δρmin = −3.8 (5) e Å^−3
72 parameters	Extinction correction: Type 1 Lorentzian isotropic (Becker and Coppens, 1974)
0 restraints	Extinction coefficient: 7 (1)

Special details

Refinement. Because of heavy Ba atoms and weak dataset anisotropic refinement of carbon and oxygen was not possible.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ba1	0.9558 (1)	0.2093 (1)	0.2782 (2)	0.0088 (7)
Ba2	0.3635 (1)	0.4185 (1)	0.2133 (2)	0.0080 (7)
C1	0.924 (2)	0.677 (2)	0.176 (3)	0.011 (3)*
C2	0.820 (2)	0.627 (2)	0.325 (3)	0.012 (3)*
O1	0.875 (1)	0.686 (1)	−0.019 (2)	0.016 (3)*
O2	1.047 (1)	0.696 (1)	0.267 (2)	0.013 (2)*
O3	0.747 (1)	0.540 (1)	0.238 (2)	0.009 (2)*
O4	0.819 (2)	0.673 (1)	0.524 (2)	0.020 (3)*
C3	0.276 (2)	0.820 (2)	0.136 (2)	0.005 (3)*
C4	0.287 (2)	0.817 (2)	0.385 (3)	0.013 (3)*
O5	0.356 (1)	0.689 (1)	0.029 (2)	0.010 (2)*
O6	0.185 (1)	0.950 (1)	0.050 (2)	0.014 (2)*
O7	0.370 (1)	0.685 (1)	0.475 (2)	0.010 (2)*
O8	0.199 (1)	0.947 (1)	0.486 (2)	0.015 (2)*
O9	0.516 (2)	0.070 (1)	0.220 (2)	0.023 (3)*
H1	0.648	0.024	0.302	0.03*
H2	0.413	0.101	0.306	0.04*	0.5
H3	0.457	0.082	0.132	0.04*	0.5

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba1	0.0104 (6)	0.0060 (6)	0.0123 (6)	−0.0053 (5)	0.0014 (5)	0.0025 (4)
Ba2	0.0080 (6)	0.0070 (6)	0.0116 (6)	−0.0053 (5)	0.0011 (4)	0.0020 (4)

Geometric parameters (Å, º)

Ba1—O6^i	2.735 (11)	Ba2^v—O4	2.776 (12)
Ba1—O8^i	2.752 (11)	C1—O1	1.231 (18)
Ba1—O1^ii	2.754 (11)	C1—O2	1.239 (19)
Ba1—O4^iii	2.763 (12)	C1—C2	1.57 (2)
Ba1—O3	2.819 (10)	C2—O3	1.267 (18)
Ba1—O2^iii	2.855 (10)	C2—O4	1.260 (18)
Ba1—O6^iv	2.878 (11)	C3—O6	1.248 (17)
Ba1—O8^v	2.896 (11)	C3—O5	1.265 (16)
Ba1—O5^iv	2.989 (11)	C3—C4	1.53 (2)
Ba2—O5^iv	2.736 (10)	C4—O8	1.258 (18)
Ba2—O7^v	2.744 (11)	C4—O7	1.261 (18)
Ba2—O1^iv	2.769 (12)	Ba2^iv—O5	2.736 (10)
Ba2—O4^v	2.776 (12)	Ba2—O5	2.806 (10)
Ba2—O5	2.806 (10)	Ba1^iv—O5	2.989 (11)
Ba2—O7	2.830 (10)	Ba1^viii—O6	2.735 (11)
Ba2—O3^iv	2.852 (10)	O6—H1^iv	2.796 (11)
Ba2—O2^vi	2.859 (11)	Ba1^iv—O6	2.878 (11)
Ba2—O9	2.905 (12)	Ba2^v—O7	2.744 (11)
C1—O1	1.231 (18)	Ba2—O7	2.830 (10)
Ba1^ii—O1	2.754 (11)	O8—H1^v	1.857 (11)
Ba2^iv—O1	2.769 (12)	Ba1^viii—O8	2.752 (11)
C1—O2	1.239 (19)	O8—O9^v	2.880 (17)
Ba1^iii—O2	2.855 (10)	Ba1^v—O8	2.896 (11)
Ba2^vii—O2	2.859 (11)	O9—H1	1.123 (13)
C2—O3	1.267 (18)	O9—H3	0.690 (13)
Ba1—O3	2.819 (10)	O9—H2	1.000 (13)
Ba2^iv—O3	2.852 (10)	O9—H3^ix	2.445 (12)
C2—O4	1.260 (18)	Ba2—O9	2.905 (12)
O4—H2^v	2.429 (12)	O9—O9^ix	2.93 (2)
Ba1^iii—O4	2.763 (12)
O6^i—Ba1—O8^i	58.4 (3)	O5—Ba2—O7	58.0 (3)
O1^ii—Ba1—O6^i	70.9 (3)	O3^iv—Ba2—O5	62.9 (3)
O4^iii—Ba1—O6^i	98.0 (3)	O2^vi—Ba2—O5	67.6 (3)
O3—Ba1—O6^i	140.4 (3)	O5—Ba2—O9	147.0 (3)
O2^iii—Ba1—O6^i	131.0 (3)	O3^iv—Ba2—O7	118.7 (3)
O6^i—Ba1—O6^iv	63.6 (4)	O2^vi—Ba2—O7	62.0 (3)
O6^i—Ba1—O8^v	100.6 (3)	O7—Ba2—O9	138.7 (3)
O5^iv—Ba1—O6^i	101.9 (3)	O2^vi—Ba2—O3^iv	82.2 (3)
O1^ii—Ba1—O8^i	107.1 (3)	O3^iv—Ba2—O9	100.4 (3)
O4^iii—Ba1—O8^i	77.4 (3)	O2^vi—Ba2—O9	141.9 (3)
O3—Ba1—O8^i	154.2 (3)	O2^vi—Ba2—O9	141.9 (3)
O2^iii—Ba1—O8^i	73.9 (3)	Ba1^ii—O1—C1	115.4 (10)
O6^iv—Ba1—O8^i	100.0 (3)	Ba2^iv—O1—C1	124.9 (10)
O8^i—Ba1—O8^v	68.4 (4)	Ba1^iii—O2—C1	119.1 (9)
O5^iv—Ba1—O8^i	142.5 (3)	Ba2^vii—O2—C1	112.6 (10)
O1^ii—Ba1—O4^iii	61.0 (3)	Ba1—O3—C2	112.0 (9)
O1^ii—Ba1—O3	74.6 (3)	Ba2^iv—O3—C2	116.5 (9)
O1^ii—Ba1—O2^iii	117.4 (3)	Ba1^iii—O4—C2	123.1 (10)
O1^ii—Ba1—O6^iv	100.2 (3)	Ba2^v—O4—C2	116.4 (10)
O1^ii—Ba1—O8^v	171.4 (3)	O1—C1—O2	128.3 (15)
O1^ii—Ba1—O5^iv	93.3 (3)	C2—C1—O1	115.2 (14)
O3—Ba1—O4^iii	81.6 (3)	C2—C1—O2	116.4 (13)
O2^iii—Ba1—O4^iii	58.4 (3)	O3—C2—O4	125.2 (14)
O4^iii—Ba1—O6^iv	158.3 (3)	C1—C2—O3	118.1 (13)
O4^iii—Ba1—O8^v	123.2 (3)	C1—C2—O4	116.7 (13)
O4^iii—Ba1—O5^iv	139.9 (3)	O5—C3—O6	123.9 (13)
O2^iii—Ba1—O3	82.5 (3)	C4—C3—O6	118.5 (13)
O3—Ba1—O6^iv	105.0 (3)	C4—C3—O5	117.6 (13)
O3—Ba1—O8^v	112.8 (3)	O7—C4—O8	124.1 (14)
O3—Ba1—O5^iv	61.0 (3)	C3—C4—O8	116.2 (13)
O2^iii—Ba1—O6^iv	142.2 (3)	C3—C4—O7	119.4 (13)
O2^iii—Ba1—O8^v	69.1 (3)	Ba2^iv—O5—C3	132.7 (9)
O2^iii—Ba1—O5^iv	124.1 (3)	Ba2—O5—C3	113.9 (8)
O6^iv—Ba1—O8^v	74.0 (3)	Ba1^iv—O5—C3	85.8 (8)
O5^iv—Ba1—O6^iv	44.4 (3)	Ba1^viii—O6—C3	122.2 (9)
O5^iv—Ba1—O8^v	86.8 (3)	Ba1^iv—O6—C3	91.2 (8)
O5^iv—Ba2—O7^v	77.1 (3)	Ba2^v—O7—C4	133.4 (10)
O1^iv—Ba2—O5^iv	110.8 (3)	Ba2—O7—C4	112.9 (9)
O4^v—Ba2—O5^iv	144.8 (3)	Ba1^viii—O8—C4	122.6 (10)
O5^iv—Ba2—O5	73.5 (3)	Ba1^v—O8—C4	91.5 (9)
O5^iv—Ba2—O7	105.3 (3)	H1—O9—H3	154.5 (16)
O3^iv—Ba2—O5^iv	71.0 (3)	H1—O9—H2	121.6 (11)
O2^vi—Ba2—O5^iv	139.7 (3)	H1—O9—H3^ix	105.9 (7)
O5^iv—Ba2—O9	74.1 (3)	O8^v—O9—H1	19.3 (5)
O1^iv—Ba2—O7^v	137.2 (3)	Ba2—O9—H1	110.5 (8)
O4^v—Ba2—O7^v	88.1 (3)	O9^ix—O9—H1	116.2 (9)
O5—Ba2—O7^v	108.5 (3)	H2—O9—H3	83.0 (12)
O7^v—Ba2—O7	70.1 (3)	H3—O9—H3^ix	50.4 (8)
O3^iv—Ba2—O7^v	148.2 (3)	O8^v—O9—H3	164.7 (13)
O2^vi—Ba2—O7^v	124.7 (3)	Ba2—O9—H3	79.2 (10)
O7^v—Ba2—O9	69.7 (3)	O9^ix—O9—H3	39.9 (7)
O1^iv—Ba2—O4^v	60.7 (3)	H2—O9—H3^ix	121.1 (9)
O1^iv—Ba2—O5	114.1 (3)	O8^v—O9—H2	109.4 (8)
O1^iv—Ba2—O7	138.6 (3)	Ba2—O9—H2	78.1 (7)
O1^iv—Ba2—O3^iv	58.4 (3)	O9^ix—O9—H2	113.7 (11)
O1^iv—Ba2—O2^vi	77.2 (3)	O8^v—O9—H3^ix	124.0 (5)
O1^iv—Ba2—O9	72.4 (3)	Ba2—O9—H3^ix	117.2 (4)
O4^v—Ba2—O5	141.7 (3)	O9^ix—O9—H3^ix	10.4 (2)
O4^v—Ba2—O7	99.2 (3)	Ba2—O9—O8^v	94.2 (4)
O3^iv—Ba2—O4^v	118.0 (3)	O8^v—O9—O9^ix	133.9 (7)
O2^vi—Ba2—O4^v	74.5 (3)	Ba2—O9—O9^ix	109.7 (6)
O4^v—Ba2—O9	70.8 (3)

Symmetry codes: (i) x+1, y−1, z; (ii) −x+2, −y+1, −z; (iii) −x+2, −y+1, −z+1; (iv) −x+1, −y+1, −z; (v) −x+1, −y+1, −z+1; (vi) x−1, y, z; (vii) x+1, y, z; (viii) x−1, y+1, z; (ix) −x+1, −y, −z.