Hydration of Lanthanide Chloride Salts: A Quantum Chemical and Classical Molecular Dynamics Simulation Study

We present the results of a quantum chemical and classical molecular dynamics simulation study of some solutions containing chloride salts of La3+, Gd3+, and Er3+ at various concentrations (from 0.05 to 5 M), with the purpose of understanding their structure and dynamics and analyzing how the coordination varies along the lanthanide series. In the La-Cl case, nine water molecules surround the central La3+ cation in the first solvation shell, and chloride is present only in the second shell for all solutions but the most concentrated one (5 M). In the Gd3+ case, the coordination number is similar to 8.6 for the two lowest concentrations (0.05 and 0.1 M), and then it decreases rapidly. In the Er3+ case, the coordination number is 7.4 for the two lowest concentrations (0.05 and 0.1 M), and then it decreases. The counterion Cl- is not present in the first solvation shell in the La3+ case for most of the solutions, but it becomes progressively closer to the central cation in the Gd3+ and Er3+ cases, even at low concentrations.