Acta Crystallographica Section B

Structural Science

Volume 58, Part 5 (October 2002)

research papers

Acta Cryst. (2002). B58, 808-814 [ doi:10.1107/S0108768101020717 ]

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

A. N. Christensen, R. G. Hazell and I. C. Madsen

Abstract: The synthesis of BaC₂O₄·0.5H₂O and its thermal decomposition to [alpha] -BaC₂O₄ and [beta] -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, [alpha] = 95.094 (3), [beta] = 95.492 (3), [gamma] = 64.500 (3)°, space group P $\bar 1$ , 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 [alpha] -BaC₂O₄. The X-ray powder pattern of [alpha] -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, [alpha] = 83.57 (4), [beta] = 98.68 (5), [gamma] = 99.53 (5)°, and the space group P $\bar 1$ with Z = 4.

Keywords: powder diffraction; profile refinement; thermal decomposition.