Three coordination compounds with urea (CO(NH2)2) ligands, namely [Cr(urea)6](ClO4)3, [Cr(urea)6](BF4)3, and [Cr(urea)6]Cl3 were
investigated. In the temperature range of 130–320 K only the first two aforementioned complexes undergo one solid phase transition at: T
h
C
=298.4 K and T
h
C=255.4 K (on heating), respectively. X-ray single crystal diffraction at 293 K demonstrates that [Cr(urea)6](BF4)3
crystallises in the trigonal crystal system (R-3c space group) and is isostructural with the other two title compounds. Both the BF4
anions
and CO(NH2)2 ligands are in the high temperature phase dynamically disordered. [Cr(urea)6](ClO4)3, [Cr(urea)6](BF4)3 and [Cr(urea)6]Cl3
are thermally stable up to ca. 500, 470 and 440 K, respectively, in argon atmosphere. [Cr(urea)6](ClO4)3 decomposes explosively at ca. 550
K. [Cr(urea)6](BF4)3 decomposes in three main stages with creation of Cr2O3 as a final product of decomposition at 1250 K. Whereas
[Cr(urea)6]Cl3 decomposes in two main stages. The mixture of Cr, CrCl3 and ClCrNH is created at 1270 K as a product of decomposition
Key words: hexakis(urea-O)chromium(III) complexes; crystal structure; vibrational and electronic spectroscopy; phase transition;
thermal decomposition
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