Two complexes of Sm(II) with crown ethers—electrochemical synthesis, structure and spectroscopy

摘要

Two complexes of divalent samarium have been synthesized by electrochemical reduction in methanol–tetrahydrofuran solutions: [Sm(18-crown-6)(ClO_4)_2] and [Sm(15-crown-5)_2](ClO_4)_2. In [Sm(18-crown-6)(ClO_4)_2] the metal cation is ten-coordinate and its coordination sphere comprises six oxygen atoms of the crown ligand and four oxygen atoms from two perchlorate anions. [Sm(15-crown-5)_2](ClO_4)_2 shows a sandwich structure with decacoordinate samarium located between two 15-crown-5 molecules. At 77 K both compounds show f–f luminescence originating from the ~5D_0 level, and also the 15-crown-5 complex shows a weak luminescence in the range 20000–25000 cm~(–1), which has been tentatively interpreted as originating from 3P0 and 5H3 levels. At room temperature the emission of [Sm(15-crown-5)_2](ClO_4)_2 is dominated by broad f–d bands. In the excitation spectra some Fano resonances have been observed. The 18-crown-6 compound is unstable, but the 15-crown-5 compound is fairly stable in air.