β-Cyclodextrin inclusion of europium(III) tris(β-diketonate)-bipyridine

The adduct Eu(NTA)(3) center dot bipy was prepared by the reaction of Eu(NTA)(3) center dot 2H(2)O with 2,2 '-bipyridine in a 1:1 ratio in chloroform [NTA = 1-(2-naphthoyl)-3,3,3-trifluoroacetonate]. Recrystallization of the complex from a chloroform/diethyl ether solvent mixture gave crystals suitable for X-ray diffraction. The Structure contained chloroform Molecules in partially occupied sites and was found to be different from the two forms previously reported for the same adduct (one unsolvated and the other containing isopropanol molecules). A single eight-coordinate geometry Was found for Eu(NTA)3 center dot bipy center dot 0.44CHCl(3), corresponding to a distorted square antiprism, with the bidentate ligands spanning opposite sides of the 'square' faces. A 2:1 (host-to-guest) inclusion compound comprising beta-cyclo-dextrin (CD) and Eu(NTA)(3) center dot bipy was obtained by co-precipitation from a mixed water/ethyl acetate solvent mixture. The formation of a true inclusion complex was supported by powder XRD, thermogravimetric analysis and C-13 CP MAS NMR spectroscopy. Photoluminescence spectroscopy indicated the presence of only one low-symmetry environment for the Eu3+ cations in non-included Eu(NTA)(3) center dot bipy and the inclusion compound. However, upon encapsulation of the complex in beta-CD, some of the Eu3+ intra-4f(6) D-5(0) -> F-7(0-4) lines shifted in energy, and the number of Stark components for the D-5(0) -> F-7(1 2) transitions increased, indicating a lowering of the symmetry of the Eu3+ local coordination environment. The room temperature excitation spectrum of the inclusion compound revealed an enhancement of the Eu3+ sensitized process as a result of encapsulation of the Eu(NTA)(3) center dot bipy molecules. (c) 2005 Elsevier Ltd. All rights reserved.