THERMAL DECOMPOSITION OF HEXACIDOCOBALTATES OF HEXAUREACHROME (III)

DOI: 10.6060/tcct.20165911.5380
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 11. P. 55-62

Double complex compounds having the [Cr(ur)6][Co(C2O4)3]4H2O (I) and [Cr(ur)6][Co(CN)6]3H2O (II) compositions were synthesized and characterized using the IR spectroscopy, elemental analysis, X-ray diffraction, crystal optical and thermal analyses. The compound I is anisotropic turquoise crystals with a needle and needle-fiber shape and a length of 5 – 15 m. The refractive indixes are N`p = 1.53; N`g = 1.56. The compound II is anisotropic lamellar pale-green crystals with refractive indixes of N`p = 1.55; N`g = 1.64. Ac-cording to thermal analysis curves, the crystallization water is removed the first. The dehy-drated products are resistant up to 170-180С. There is a fast weight loss from 200 to 300C, which is almost the same in both cases (about 37%). The residue of the complex I after calci-nation is 20.9% in air and 16.1% in argon. For complex II, they are 23.6% and 26.4%, re-spectively. A comparative study of the thermolysis for these complexes in air, argon, and hy-drogen was carried out. The gaseous and solid thermolysis products of the complexes for dif-ferent temperature ranges were analyzed. It was determined that the gaseous thermolysis products are NH3, СО, CO2, HCN, and HCNO. Regardless of the medium, the thermolysis of complex I gives an intermediate with a composition of Cr(ur)Co(C2O4)3 at the temperature of about 300 °C. The amount of carbon released as CO and CO2 and remaining in the solid res-idue at all temperatures is close to 70%, so at least 30% is the urea released in the invariable form and as isocyanic acid and others. This also applies to complex II. The urea behaves identically in both cases. At thermolysis of complex II, no intermediate is formed and in the inert environment, the amount of original carbon, remaining in the solid residue, is much greater than for I, due to decomposition of cyano groups with nitrogen emission. As a result of thermolysis in atmospheric air and in hydrogen, both the compounds give products with similar carbon contents. Substituting of iron on cobalt in the composition of the complex ani-on has no appreciable effect on the course of the thermolysis of either the oxalate or cyanide complex.

Key words: double complex, synthesis, thermolysis, analysis, urea, intermediate

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2016, Т. 59, № 11, Стр. 55-62

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