Crown-Ether Coordination Compounds of Europium and 24-Crown-8

Crown-ether coordination compounds of europium(II/III) and the crown ether (C2H4O)8 (24-crown-8, 24c8) are prepared, aiming at novel compounds, structures, and coordination modes as well as potential luminescence properties. By reacting EuCl2, EuI2, or EuCl3 with 24c8 or its derivatives in ionic liquids, the novel compounds [Bu3MeN]2[Eu(II)(NTf2)4] (1), [BMIm]6[Eu3I12] (2), [EuCl2(dibenzo-18c6)] (3), [EuI2(dibenzo-24c8)] (4), [(Eu(III)Cl3)2(C14H30O8)](24c8) (5), and [Eu(III)Cl(24c8)]I2 (6) are obtained (BMIm: 1-butyl-3-methylimidazolium; EMIm: 1-ethyl-3-methylimidazolium). Based on different reaction conditions, different coordinative modes including the absence of the crown ether in the product (1, 2), splitting of the crown ether (5), and coordination of 24c8 via six of eight oxygen atoms (4) and, finally, via all oxygen atoms (6) are observed. Crystallization of the title compounds is generally difficult, which can be attributed to the flexibility of the crown-ether molecule that can be rotated around all 24 tetrahedral (C) and pseudo-tetrahedral (O) centers. Besides structural characterization via single-crystal structure analysis and X-ray powder diffraction with Rietveld refinement, compounds 1–6 are examined by infrared spectroscopy and thermal analysis. The title compounds show blue to red emission, and the influence of structure and coordinative mode on the luminescent properties is analyzed.