Electronic and ESR spectroscopic study of thiocyanate-containing coordination compounds of titanium(III) in alcohol solutions

Abstract

In an investigation of electronic and ESR spectra, it has been established that titanium(III) with the thiocyanate ion (in ethanol) forms distorted tetrahedral and octahedral complexes. The tetrahedral compounds, which are hydroxo complexes of titanium(III) that contain one hydroxyl group and three thiocyanate ions in the coordination sphere, give signals in the ESR spectra with g_o=1.960, A_o=15.0·10⁻⁴ cm⁻¹ g_∥=1.958, A ^Ti_∥ =26.4·10⁻⁴cm⁻¹, g= 1.691, A^Ti=9.0·10⁻⁴ cm⁻¹. In the ESR spectra of liquid solutions, additional splitting on the nitrogen atoms is manifested(A ^N_o =2.2·10⁻⁴ cm⁻¹), which indicates bonding of thiocyanate ions through the nitrogen atom. The pseudo-octahedral complexes of titanium(III), containing from two to six thiocyanate ions in the coordination sphere, are characterized by d-d absorption bands in the 520–590 nm region; and at 77°K, they give anisotropic ESR signals. On the basis of the temperature dependences of the equilibrium constants for the reaction of conversion of the tetrahedral complexes to the octahedral complexes, and also the lifetimes of the tetrahedral complexes, values have been estimated for the heat of reaction (ΔH=26.8 kJ/mole) and the entropy change (ΔS=−1.66 kJ/mole·°K) of the equilibrium process, and also the activation energy for the reaction of titanium(III) thiocyanate formation (ΔE=37 kJ/mole).