The Missing Link Crystallized from the Ionic Liquid 1-Ethyl-3-methylimidazolium Tosylate: Bis-aqua-(p-toluenesulfonato-O)-europium(III)-bis-p-toluenesulfonate Dihydrate

Bis-aqua-(p-toluenesulfonato-O)-europium(III)-bis-p-toluenesulfonate-dihydrate (1) was synthesized and structurally characterized. The crystal structure contains eight-coordinate europium(III) atoms. One oxygen atom from p-toluenesulfonate and seven aqua ligands form a slightly distorted square antiprism around Eu(III). A variety of O−H···O and intermolecular C−H···O hydrogen bonds link the asymmetric units into a two-dimensional layer, and these layers are further assembled into a three-dimensional supramolecular structure through intermolecular C−H···O hydrogen bonds and edge-to-face C−H···π interactions. The compound represents the structural missing link between the well-known lanthanide (Ln) tosylate (Tos) hydrates [(Ln(H₂O)₉](p-Tos)₃(H₂O) with noncoordinating tosylate and [Ln(H₂O)₆(p-Tos)₂](p-Tos)₂(H₂O)₃ where two tosylate groups coordinate to the lanthanide cation. It is another example how unusual coordination environments can be trapped by the use of ionic liquids.