Electron spin relaxation in the study of boundary layers at the liquidsolid interphase

Abstract

The electron spin relaxation of transition metal ions is largely sensitive towards structural changes of the complex and towards mobility alterations of the solvent. In the case of Cu(II) (S = 1 2 ), structural changes influence both the magnetic parameters ( g and A tensors) and the line width as a consequence of the relaxation mechanisms dominating in solution (spin-rotation and A and g anisotropies modulation). Solvent mobility variations also alter the line width, at low and high temperature, in opposite ways. In the case of Mn(II) (S = 5 2 , structural changes influence the zero-field splitting term, thus effecting the line width, without appreciably modifying the line position (static term in the spin Hamiltonian). Decreased solvent mobility increases the correlation time for the motion and therefore the line width (dynamic term in the spin Hamiltonian). The liquid mobility at the solidliquid interface is expected to be decreased and to induce large effect on the line width of paramagnetic probes in the boundary layers. From a line width analysis, the correlation times for the motion can be calculated as a function of the distance from the surface. The above procedure is applied to liquid-solid interphase in which SiO 2, Al 2O 3, TiO 2, and carbon were the porous solid supports, and water, NaOH water solution, and organic fluids were the liquids. The probes used were Mn(H 2O) 2+ 6, Cu(H 2O) 2+ 2, Cu(OH) 2− 4, and Cu(acac) 2.