SPECTROSCOPIC, STRUCTURAL AND THERMAL CHARACTERIZATION OF CRYSTALLINE [Cr(OC(NH2)2)6]X3, WHERE X = ClO4-, BF4- and Cl-

摘要

Three coordination compounds with urea (CO(NH 2 ) 2 ) ligands, namely [Cr(urea) 6 ](ClO 4 ) 3 , [Cr(urea) 6 ](BF 4 ) 3 , and [Cr(urea) 6 ]Cl 3 were investigated. In the temperature range of 130–320 K only the first two aforementioned complexes undergo one solid phase transition at: = 298.4 K and = 255.4 K (on heating), respectively. X-ray single crystal diffraction at 293 K demonstrates that [Cr(urea) 6 ](BF 4 ) 3 crystallises in the trigonal crystal system ( R -3 c space group) and is isostructural with the other two title compounds. Both the BF 4 - anions and CO(NH 2 ) 2 ligands are in the high temperature phase dynamically disordered. [Cr(urea) 6 ](ClO 4 ) 3 , [Cr(urea) 6 ](BF 4 ) 3 and [Cr(urea) 6 ]Cl 3 are thermally stable up to 500, 470 and 440 K, respectively, in argon atmosphere. Above these temperatures [Cr(urea) 6 ](BF 4 ) 3 and [Cr(urea) 6 ]Cl 3 decompose in two main steps. In the first step six urea molecules are liberated and in the second step metallic chromium is created. Whereas [Cr(urea) 6 ](ClO 4 ) 3 decomposes explosively just at ca. 550 K.