Anhydrous, Homoleptic Lanthanide Frameworks with the Pentafluoroethyltricyanoborate Anion

Pentafluoroethyltricyanoborate frameworks of rare-earth metal ions of the general formula [Ln{C2F3B(CN)(3)}(3)(OH2())] (Ln = La, Eu, Ho; n = 0, 3; [Ln1(3)(OH2)]) were synthesized using the oxonium salt (H3O) [C2F3B (CN)(3)] ((H3O)1) and lanthanide chlorides LnC13.111120 as starting compounds. Single-crystals of (3)(infinity)[La{C2F5B(CN)(3)}(3)] ((3)(infinity)[La1(3)]) are obtained from the room temperature ionic liquid (RTIL) [EMIm]1 using either a ionothermal approach or by recrystallization of anhydrous microcrystalline [La1(3)] that is obtained from reactions in aqueous media after drying in a vacuum. Removal of water from [Ln1(3)(OH2)(3)] (Ln = Eu, Ho) to give microcrystalline (3)(infinity)[Ln1(3)] is achieved in a vacuum at elevated temperatures. All compounds were characterized by vibrational and NMR spectroscopy, thermogravimetry, and elemental analysis. The structures of the three-dimensional coordination polymers (3)(infinity)[Eu1(3)(OH2)(3)] and (3)(infinity)[La1(3)] were elucidated by single-crystal X-ray-diffraction. According to powder diffraction studies on anhydrous 3[Ln1(3)] (Ln = La, Eu, Ho), the three compounds are isotypic. A study of the photoluminescence properties reveals that both Eu3+ compounds, [Eu1(3)] and [Eu1(3)(OH2)(3)], are strongly luminescent, the emission of the anhydrous framework being significantly more intense than the one of the hydrate. The Eu-compounds benefit from a sensitizer effect of the anion. In contrast, the Ho-containing framework (3)(infinity)[Ho13] exhibits separate chromophores and a strong reabsorption of the fluorescence by the Ho3+ ions.