NMR B coefficients for monovalent ions in DMSO solutions at 30, 45 and 65 °C

Abstract

¹⁷O spin–lattice relaxation times (T₁) of dimethyl sulfoxide (DMSO) have been measured in DMSO–electrolyte [MBr (M=Li–Cs), KI, KClO₄, R₄NBr (R=Et, Bu, Hex, Hep), Ph₄PBr, Bu₄NPh₄B, Bu₄NBu₄B] solutions in the concentration range 0.10.3 mol kg^-1 at 30, 45 and 65 °C. The NMR B coefficients for the electrolytes were obtained from the concentration dependence of the relaxation rate ratios of the solutions to those of pure solvent (R₁/R₁⁰=T₁⁰/T₁). The B coefficients were broken down to give ionic B coefficients with an assumption of B(Bu₄N⁺)=B(Bu₄ B^-) at each temperature. The following features are seen in the ionic B coefficients for DMSO: (i) the B coefficients are always positive; (ii) for alkali-metal and halide ions, the B values decrease with increasing surface area of the ion; (iii) the B values for alkali-metal ions are larger than those for tetraalkylammonium ions; (iv) for tetraalkylammonium ions, the B values increase with increasing surface area of the ions; (v) the temperature dependences of the B coefficients for almost all the ions studied are very small. Based on these results, we discuss the effect of the ionic charge and size on the ionic B coefficients in a simple aprotic solvent.