Ionothermal Synthesis of Tetranuclear Borate Clusters Containing <i>f</i>- and <i>p</i>‑Block Metals

Abstract

The reactions of simple oxides or halides of trivalent lanthanides and actinides or bismuth with boric acid in the ionic liquid 1-butyl-3-methyl­imid­azolium chloride at 150 °C result in the formation and crystallization of a series of isomorphous tetranuclear borate clusters with the general formula M₄B₂₂O₃₆(OH)₆(H₂O)₁₃ (M = La, Ce, Pr, Nd, Sm, Eu, Gd, Pu, and Bi). These clusters do not assemble with trivalent cations smaller than Gd³⁺, suggesting that the formation of the clusters is dictated by the size of the metal ion. The cations are found in cavities along the periphery of a cage assembled from the corner- and edge-sharing interactions of BO₃ triangles and BO₄ tetrahedra, yielding a complex chiral cluster. Both enantiomers cocrystallize. The metal ions are nonacoordinate, and their geometries are best described as distorted tridiminished icosahedra. This coordination environment is new for both Pu³⁺ and Bi³⁺. In addition to detailed structural information, UV/vis–NIR absorption and photoluminescence spectra are also provided