MONTE-CARLO SIMULATIONS OF THE TRIPOSITIVE LANTHANIDE IONS IN AQUEOUS-SOLUTION

Monte Carlo simulations have been carried out for tripositive lanthanide ions in aqueous solutions. Two different types of effective water-oxygen lanthanide-ion pair potentials were tested to reproduce experimental ion-oxygen distances. Despite the simple character of the potentials used, a change in coordination number from nine to eight for the first coordination sphere was found along the series with both potentials. In addition, water exchange between the first and the second coordination shells was detected and led to a mechanistic conclusion that agreed with results from variable-pressure NMR experiments for the heavy octa-aqua lanthanides (I, mechanism) and the prediction of a dissociative mechanism for the ennea-aqua ions.