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Coordination Chemistry and Photoluminescence of Sm(II) Dibenzo-24-crown-8 Complexes
Hannah B Wineinger1, Kacy N Mendoza1, Jacob P Brannon1
1Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States.
Abstract:
Three Sm(II) dibenzo-24-crown-8 (db24c8) complexes were synthesized in anhydrous, air-free conditions via the reaction of SmI2 with db24c8 and tetrabutylammonium tetraphenylborate ([TBA][BPh4]; where needed) in acetonitrile (CH3CN), dimethoxyethane (DME), and tetrahydrofuran (THF) to yield [Sm(db24c8)(CH3CN)2][BPh4][I]·CH3CN, [Sm(db24c8)(DME)]I2, and [Sm(db24c8)(THF)2]I2, respectively. In each case, a 10-coordinate, staggered dodecahedral (2:6:2) environment is formed around the Sm2+ center that is completed by either two solvent molecules (CH3CN or THF) or one bidentate solvent molecule (DME). Inner-sphere solvent molecules can be excluded by reacting SmI2 with db24c8 in 1:3 THF:toluene to yield Sm(db24c8)I2. This molecule features a distorted, eight-coordinate, hexagonal pyramidal Sm2+ metal center, where the coordinated db24c8 molecule shows a torsion angle unexpectedly close to the 180° antiperiplanar arrangement and two uncoordinated db24c8 oxygen atoms. Solution UV-vis-NIR measurements demonstrate that Sm2+ is a good size match for the cavity of various db24c8 conformations and that Eu2+ and Yb2+ exhibit competition between acetonitrile solvation and the Eu2+ and Yb2+/db24c8 complexes in solution. During excitation by 546 nm light, both [Sm(db24c8)(DME)]I2 and [Sm(db24c8)(THF)2]I2 exhibit mixed 5d → 4f and 4f → 4f emission at 20 °C and exclusively 4f → 4f at -180 °C, whereas Sm(db24c8)I2 only shows 5d → 4f emission regardless of temperature. Photoluminescence from [Sm(db24c8)(CH3CN)2][BPh4][I]·CH3CN is quenched.
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