Ionothermal synthesis of tetranuclear borate clusters containing f- and p-block metals.

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 Gd(3+), 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 Pu(3+) and Bi(3+). In addition to detailed structural information, UV/vis-NIR absorption and photoluminescence spectra are also provided.

1-Ethyl-3-methyl-1H-imidazol-3-ium spiro-penta-borate.

In the anion of the title compound, (C6H11N2)[B5O6(OH)4], both six-membered borate rings adopt a flattened boat conformation with the spiro-B atom and its opposite O atom deviating from the remainders of the rings by 0.261 (3)/0.101 (2) and 0.160 (3)/0.109 (2) Å, respectively. The imidazolium cation also deviates from planarity due to rotation of the ethyl group (as indicated by the C-N-C-C torsion angle) by 71.4 (2)° out of the plane of the heterocycle. In the crystal, the anions are connected in a three-dimensional network through O-H⋯O hydrogen bonds, forming channels along the a-axis direction. The cations are situated in the channels, forming C-H⋯O hydrogen bonds with the anions.