Solvation Structure of the Ti(III) Ion in Methanol Solutions and in Perfluorinated Ionomers Swollen by Water and Methanol. A Study by ESR and ENDOR

Abstract

Abstract The local environment of Ti3+ cations in methanol solutions and in Nafion perfluorinated ionomers swollen by water and methanol has been studied by electron spin resonance (ESR) and by 1H and 2H electron nuclear double resonance (ENDOR) spectroscopies. The two major sites reflecting the ligation of the cations as a function of solvent structure and cation concentration have been analyzed, using whenever possible the method of orientation selection for the ENDOR transitions. The distance RN of the protons from the central cation, and the angle ΘN between the symmetry axis of Ti3+ and the Ti3+ -proton vector have been deduced by evaluating the dipolar interaction tensor and by simulating the orientation dependence of the ENDOR signal. For site 1 of Ti3+ in methanol (g॥ = 1.986 and g⊥ = 1.894) no orientation selection was possible, and RN values in the range 4.1 to 4.6 Å are suggested from the ENDOR splittings. For site 2 of Ti3+ in methanol (g॥ = 1.943 and g⊥ = 1.960) equatorial and axial methyl protons have been detected; the RN values deduced from the simulations are 3.95 and 4.35 Å, respectively. For Ti3+ in Nafion swollen by water (g || = 1.997 and g⊥ = 1.907), equatorial and axial protons from OH groups have been detected, and the ENDOR spectra were simulated with RN values of 2.60 and 3.10 Å respectively for these protons