BaC4O44 — An Alkaline-Earth Squarate Free from Water of Crystallization with Three-dimensional Framework Structure Featuring a Layer-like Separation of Cations and Anions

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Abstract.

Z. Anorg. Allg. Chem. 629 (2003) 371-373. (DOI: 10.1002/zaac.200390061).

Colourless single crystals of BaC4O4 have been obtained from aqueous solution at 80 °C. BaC4O4 is stable in air up to 490 °C. BaCO3 is formed by further increase of temperature. BaC4O4 crystallizes in the tetragonal space group I4/mcm (nr. 140) with a=635.95(5),
c=1240.77(13) pm, Z=4. Ba2+ is coordinated by eight oxygen atoms of the squarate dianions; Ba—O 276.1(1) pm. The coordination polyhedron is a distorted, square anti-prism. The squarate dianions occupy crystallographic mirror planes and posses approximately 4/mmm symmetry; C—C 145.7(5) and 146.5(5) pm, C—O 125.9(3) pm. A layer-like separation between the cations and anions exists with respect to the [001] direction.

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