Variation of relaxation parameters of aqueouslanthanide nitrates across the series

Abstract

The dependencies of relaxations parameters( the relaxation frequency f_R, the velocity dispersion c_-c₀ and the values c₀-c_H2O ) for lanthanide nitrate solutions across the series were determined. Nonlinear dependence of these parameters was observed. The relaxation frequency reaches a maximum on samarium and then falls down to the heaviest lanthanides. The value c₀-c_H2O shows minimum in the solutions of Sm(NO₃)₃. The magnitude of the ultrasound velocity dispersion also describes nonlinear dependence across the series. Using the interpretation that the dispersion in the lanthanide nitrate solutions is caused by an association process with formation of inner sphere complexes [LnNO₃]_aq²⁺, a magnitude of an ultrasound dispersion may be a quantity of complexation. The lowest dispersion was observed for erbium nitrate, so in this solutions exists the minimum of inner sphere substitutions. Hence, ultrasound velocity measurements in lanthanide nitrate solutions indicate the variation of the amount of complexes [LnNO₃]_aq²⁺ and the interaction between individual ions RE³⁺ and water molecules across the series.