Structural Variation In β-Octamolybdate Polyoxoanion Based Crystals Across Lanthanide Series Isolated from a Water/DMSO Solution.

The crystallization of lanthanide-containing β-octamolybdate (β-{Mo8O26}4-) based solids from a binary 1 : 1 (water/DMSO) solution under ambient conditions is reported. A uniform synthetic protocol yielded three structurally related series of general composition {Ln(solvent)n}[NaMo8O26] ⋅ yH2O, with the whole lanthanide series (except for radioactive Pm). The three series are (i) {Ln(DMSO)8}[NaMo8O26] ⋅ 0.5H2O, Ln=La, Ce, Pr, Nd and Sm (Series C1); (ii) {Ln(DMSO)6(H2O)2}[NaMo8O26] for Ln=Eu, Gd, Tb, Dy and Ho (Series C2) and (iii) [{Ln(DMSO)7}][NaMo8O26] ⋅ H2O for Ln=Dy, Ho, Er, Tm, Yb and Lu (Series C3). All solids reported here contain [-β-Mo8O26-Na-β-Mo8O26-] anionic chains, which is the dominant feature in the crystal packing of these solids. The chains interacted via hydrogen bonds with the solvated lanthanide counter cations. Lanthanide contraction brings about the difference in the primary coordination sphere of the Ln3+ cations in the three series reported here. This manifests in the crystal structure as a change in the relative orientation of chains (or clusters) and the position of Ln3+ centers, with water acting as the structure director. The study demonstrates Nature's parsimonious ability to optimize intermolecular interactions via diminutive deviations from recognizable packing patterns when a crystal nucleates from solution.