On dehydration of La[Co(CN)
6]·5H
2O, the color of the complex, changes from white to pale blue at around 230°C. Heating the pale blue specimen, the color changes
to deep blue at around 290°C. This deep blue specimen is easily rehydrated to a pink one. As reported previously, in the pale
blue specimen, Co
3+ ions are situated in the center of the D
4h crystal field formed by six CN
- ions.
The deep blue specimen is due to the presence of [Co(CN)
4]
2- ions in which Co
2+ was situated in a T
d coordination field formed by four CN
- ions and the Co-C bond length is 1.67 Ĺ. The pink species corresponded to
trans-[Co(CN)
4(H
2O)
2]
2- and the bond lengths of Co-C and Co-O are 1.89 and 1.85 Ĺ, respectively.
The Raman spectra of the complex observed at 25°C displays two bands at 2157 and 2176 cm
-1 associated with the vibration of C-N bond, and the band of 2157 cm
-1 was split into two bands, 2150 and 2156 cm
-1, at around 100°C. When the complex was heated to around 230°C, three new bands were observed at 2103, 2116 and 2141 cm-1.
The bands of 2103 and 2116 cm
-1 were assigned to the stretching vibration of C=N bonding to Co
2+. The band of 2141 cm
-1 was assigned to the stretching vibration of the inverted CN
- as follows: Co-C=N-La→Co-N=C-La. The activation energy for the inversion of CN
- was estimated as 67 kJ mol
-1.
This revised version was published online in August 2006 with corrections to the Cover Date.
相似文献