Selective Crystallization for Green Separations of Lanthanides Using 5-(Pyrimidyl)Tetrazolate

In an effort to develop facile, low-cost, and environmentally benign separations of lanthanides, the coordination chemistry and selective crystallization of Ln3+ cations with the water-soluble ligand 5-(pyrimidyl)tetrazolate (pmtz) have been investigated. The wide range of coordination modes of pmtz allows for discrimination between these cations, and five distinct compound types can be prepared that are dependent on the lanthanide employed. La3+ leads to the formation of [La(pmtz)2(H2O)6]Cl (S1). [Ln(pmtz)3(H2O)3]·(3+n)H2O is obtained with Ce3+and Pr3+ (S2). Ce3+ can also form [(Ce(pmtz)2(H2O)3)2(μ-pmtz)](pmtz)·11H2O (S3). [(Ln(pmtz)2(H2O)3)2(μ-pmtz)]2(pmtz)2·14H2O (S4) is formed with Nd3+ and Sm3+. The smaller Ln3+ cations, Dy3+ to Lu3+, all yield [Ln(H2O)8](pmtz)3·3H2O (S5). This selective crystallization of Ln3+ cations based primarily on ionic radii provides a simple method for achieving group separations.