Unexpected Coordination Chemistry of Bisphenanthroline Complexes within Hybrid Materials: A Mild Way to Eu2+ Containing Materials with Bright Yellow Luminescence

LaMg6Ga6S16: a chemical stable divalent lanthanide chalcogenide

Divalent lanthanide inorganic compounds can exhibit unique electronic configurations and physicochemical properties, yet their synthesis remains a great challenge because of the weak chemical stability. To the best of our knowledge, although several lanthanide monoxides epitaxial thin films have been reported, there is no chemically stable crystalline divalent lanthanide chalcogenide synthesized up to now. Herein, by using octahedra coupling tetrahedra single/double chains to construct an octahedral crystal field, we synthesized the stable crystalline La(II)-chalcogenide, LaMg6Ga6S16. The nature of the divalent La2+ cations can be identified by X-ray photoelectron spectroscopy, X-ray absorption near-edge structure and electron paramagnetic resonance, while the stability is confirmed by the differential thermal scanning, in-situ variable-temperature powder X-ray diffraction and a series of solid-state reactions. Owing to the particular electronic characteristics of La2+(5d1), LaMg6Ga6S16 displays an ultrabroad-band green emission at 500 nm, which is the inaugural instance of La(II)-based compounds demonstrating luminescent properties. Furthermore, as LaMg6Ga6S16 crystallizes in the non-centrosymmetric space group, P-6, it is the second-harmonic generation (SHG) active, possessing a comparable SHG response with classical AgGaS2. In consideration of its wider band gap (Eg = 3.0 eV) and higher laser-induced damage threshold (5×AgGaS2), LaMg6Ga6S16 is also a promising nonlinear optical material.

First use of a divalent lanthanide for visible-light-promoted photoredox catalysis

We report the first catalytic use of a divalent lanthanide in visible-light-promoted bond-forming reactions. Our new precatalyst uses europium in the +2 oxidation state and is active in the presence of blue light from light-emitting diodes. The use of low-energy visible light reduces the occurrence of potential side reactions that might be induced by higher-energy UV light. The system described here uses zinc metal as a sacrificial reductant and is tolerant to wet, protic solvents. The catalyst can be made in situ from relatively inexpensive and air-stable EuCl3·6H2O, and the ligand can be synthesized in large quantities in two steps. With 0.5% loading of precatalyst, an average of 120 turnovers was observed in six hours for reductive coupling of benzyl chloride. We expect that the results will initiate the study of visible-light-promoted photoredox catalysis using divalent europium in a variety of reactions.

Synthesis, luminescence, and anti-tumor properties of MgSiO3:Eu-DOX-DPP-RGD hollow microspheres

In this report, MgSiO3:Eu-DOX-DPP-RGD hollow microspheres employed for simultaneous imaging and anti-cancer therapy have been designed by sequentially loading the anti-tumor drugs doxorubicin (DOX), light-activated platinum(iv) pro-drug PPD, and a targeted peptide of NH2-Gly-Arg-Gly-Asp-Ser (RGD) onto MgSiO3:Eu mesoporous hollow spheres, which were synthesized using solid SiO2 spheres as sacrificed template by a facile hydrothermal process based on the Kirkendall effect. The photoluminescence intensity of MgSiO3:Eu has been optimized, which can emit a recognized red signal in vitro and in vivo under modest ultraviolet (UV) irradiation. It was found that the platform has high biocompatibility and could become intracellular through fast and effective endocytosis with the aid of the targeted peptide RGD, and chemotherapeutic drugs DOX and light-activated platinum(iv) pro-drug DPP that can be released from the carrier to induce an obvious inhabitation effect to HeLa cancer cells (survival rate of only 17.4%), which has been verified by in vitro and in vivo results. Moreover, the in vitro result using a photosensitizer ZnPc loaded carrier shows that the system is not suitable for ZnPc induced photodynamic therapy. The apparent imaging effect and high anti-tumor efficacy of this functional system give it great potential in actual clinical applications.

Europium(II) compounds: simple synthesis of a molecular complex in water and coordination polymers with 2,2'-bipyrimidine-mediated ferromagnetic interactions

Reaction between EuCl(2) and 2,2'-bipyrimidine (bpm) in de-oxygenated water afforded a cationic molecular complex [EuCl(bpm)(2)(H(2)O)(4)][Cl]·H(2)O (1). When performed in an organic solvent such as THF or methanol, the same reaction yielded a 3-dimensional coordination polymer of formula [EuCl(2)(bpm)(MeOH)(0.5)](∞) (2) in which both bpm and the chloride ions act as linkers between the Eu(II) ions. Upon replacing Cl(-) by I(-), two coordination polymers of formula {[Eu(bpm)(2)(H(2)O)(3)][I](2)·0.5bpm}(∞) (3) and {[Eu(I)(bpm)(MeOH)][I]}(∞) (4) were obtained from reaction in water and methanol, respectively. All these compounds were characterized by X-ray crystallography. Investigations of the magnetic properties revealed a weak antiferromagnetic coupling in 2, while 3 and 4 showed a weak ferromagnetic coupling at low temperature.

Highly transparent and luminescent lanthanide ion-containing bridged polysilsesquioxanes

Novel luminescent bridged polysilsesquioxane monoliths of high transparency have been obtained by hydrolysis and condensation of the precursor under acidic conditions. The monoliths were characterized by FTIR spectroscopy, photoluminescence spectroscopy, and SEM, and they have been used as hosts of Eu(3+), Tb(3+) and Nd(3+) ions. The luminescence lifetime of Tb(3+) in this host was 2.1 ms. The interaction between the host and the lanthanide ions could be confirmed by FTIR spectra. The number of water molecules coordinated to the Eu(3+) ions was determined to be one. Incorporation of Nd(3+) as guest resulted in NIR-luminescent materials.