The coordination (hydration) of rare earth ions in aqueous chloride solutions from x-ray diffraction. III. SmCl3, EuCl3, and series behavior

Abstract

The inner sphere water coordination of Sm³⁺ and Eu³⁺ in concentrated (3.23 m) aqueous chloride solutions was obtained from x‐ray diffraction measurements at 25 °C. The average water coordination is 8.8 for Sm³⁺ and 8.3 for Eu³⁺. The average RE³⁺–H₂O distances are 2.474 Å for Sm³⁺ and 2.450 Å for Eu³⁺. The average RE³⁺⋅⋅⋅Cl⁻ ion pair distances occur near 4.9 Å. A careful examination of the x‐ray diffraction results for ten rare earth chloride solutions indicates that the inner sphere water coordination of the rare earth ions in aqueous solutions decreases from nine to eight due to the decreasing rare earth ionic radii. The ions La³⁺ through Nd³⁺ are nine coordinated, those between Nd³⁺ and Tb³⁺ are transitional between nine and eight, and those from Tb³⁺ to Lu³⁺ are eight coordinated.