The Halogen Bond to Ethers - Prototypic Molecules and Experimental Electron Density.

Halogen bonds to dialkyl ether molecules have remained largely unexplored. We here address the synthesis and the structural chemistry of the first halogen-bonded noncyclic alkyl ethers, combining 1,4-diiodotetrafluorobenzene and the prototypic or commonly used ethers dimethyl ether, tetrahydrofuran, and methyl-tert-butyl ether as halogen acceptors. Two different structural motifs based on moderately strong halogen bonds were obtained: Discrete trimolecular aggregates are formed, and unexpected halogen-bonded supramolecular chain adducts feature oxygen-bifurcated halogen bonds with 1:1 donor:acceptor ratio. Both structure types may be selectively obtained even for the same ether by adjusting the stoichiometry in the crystallization experiments. The geometric features of the etheric oxygen center were found to be flexible, in contrast to the almost linear geometry about the halogen donor atom. A high-resolution X-ray diffraction experiment on the extended adduct of dimethyl ether allowed us to study the electronic details of the acceptor-bifurcated I···O···I halogen bonds. The electron density in the bond critical points and derived properties such as the Laplacian indicate essentially electrostatic interactions and explain the geometrical flexibility of ethers in halogen bonds. Our studies demonstrate the great versatility of ethers as halogen bond acceptors, that can occur in many geometrical arrangements and whose contribution to nature's structural designs should not be underestimated.

Luminescent lanthanide complexes based on 4,5-di(3,5-dicarboxylphenoxy)phthalic acid as enhanced fluorescence probes for highly selective detection of lead(II) ions in water.

Six novel lanthanide complexes ([Nd2(L)(H2O)6]n·4.58n(H2O) (1), [Ln(H3L)(H2O)]n·0.5n(H2O), Ln = Sm (2), Eu (3), Gd (4), Tb (5), Eu0.18Gd0.62Tb0.20 (6)) have been hydrothermally synthesized based on the ligand 4,5-di(3,5-dicarboxylphenoxy)phthalic acid (H6L). Single crystal X-ray diffraction reveals that complexes 1-6 are 2D structures, where 2-6 are isomorphic. Complexes 3 and 5 exhibit the characteristic fluorescence of Eu(III) and Tb(III) ions respectively, while complex 4 shows blue-green light emission based on the ligand. In particular, the ternary Eu/Gd/Tb complex 6 shows white light emission with a CIE (Commission International del'Eclairage) chromaticity coordinate of (0.330, 0.339) and hence close to pure white light emission. Moreover, complexes 3 and 5 display specific fluorescence-enhanced detection performance for Pb2+ ions: The interaction between Pb2+ ions and the ligand enhances the charge transfer efficiency between the ligand and the Eu(III) and Tb(III) ions and thus leads to fluorescence enhancement of complexes 3 and 5. More importantly, complex 3 exhibits the lowest detection limit of 4.72 nM for Pb2+ ions among the existing complex fluorescent probes. In addition, both complexes 3 and 5 show good performance for recycling and for the detection of Pb2+ in real water samples.