Structure and Emission Properties of Er3Q9 (Q = 8-Quinolinolate)

Molecular Compounds in Spintronic Devices: An Intricate Marriage of Chemistry and Physics

Spintronics, a flourishing new field of microelectronics, uses the electron spin for reading and writing information in modern computers and other spintronic devices with a low power consumption and high reliability. In a quest to increase the productivity of such devices, the use of molecular materials as a spacer layer allowed them to perform equally well or even better than conventional all-inorganic heterostructures from metals, alloys, or inorganic semiconductors. In this review, we survey various classes of chemical compounds that have already been tested for this purpose─from organic compounds and coordination complexes to organic-inorganic hybrid materials─since the creation of the first molecule-based spintronic device in 2002. Although each class has its advantages, drawbacks, and applications in molecular spintronics, together they allowed nonchemists to gain insights into spin-related effects and to propose new concepts in the design and fabrication of highly efficient spintronic devices. Other molecular compounds that chemistry could offer in great numbers may soon emerge as suitable spacers or even electrodes in flexible magnetic field sensors, nonvolatile memories, and multifunctional spintronic devices.

Metal–organic frameworks with solvent-free lanthanide coordination environments: synthesis from aqueous ethanol solutions

Twelve MOFs with a solvent-free environment of Ln³⁺ cations were obtained through solution synthesis in the presence of cluster anions.

Quantitative Sensitization Efficiencies in NIR-Emissive Homoleptic Ln(III) Complexes Using 2-(5-Methylpyridin-2-yl)-8-hydroxyquinoline

A series of isostructural lanthanide complexes [Ln(MPQ)₃] (Ln = Nd, Gd, Er, Yb, Lu) using a monoanionic tridentate methylpyridyl-substituted 8-hydroxyquinoline ligand (MPHQ = 2-(5-methylpyridin-2-yl)-8-hydroxyquinoline) have been prepared and characterized using elemental analysis (CHN), single-crystal X-ray diffraction (XRD), and ¹H NMR spectroscopy. This ligand forms homoleptic charge-neutral lanthanide complexes with three coordinated ligands arranged in an "up-up-down" fashion around the metal center. The photophysical properties of the Nd, Er, and Yb complexes were investigated using absorption and emission spectroscopy, with the latter species displaying efficient sensitization in the Near Infra-Red (NIR) region and a photoluminescence quantum yield (PLQY) as high as 1.0% in CH₂Cl₂ solution. The intersystem crossing and energy-transfer processes involved in the antenna effect were further investigated using transient absorption techniques, which revealed essentially quantitative sensitization efficiencies for the NIR-emitting cations.

Seven phenoxido-bridged complexes encapsulated by 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands: single-molecule magnet, magnetic refrigeration and luminescence properties

Seven dinuclear complexes based on 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands have been synthesized, and structurally and magnetically characterized.

An Unexpected Coupling Reaction of 8-Quinolinolate at Elevated Temperature

Reactions of 8-hydroxyquinoline (HOQ) with elemental rare-earth and transition metal combinations or alloys at 200–300°C yielded a variety of complexes, albeit in very low yields, including two structurally characterised homometallic complexes containing an unexpected biquinolinolate ligand. Reaction of HOQ with SmCo5 alloy gives rise to the complexes [SmCo2(OQ)7] (1), [Co4(OQ)4(BQ)2] (2), and [Sm3(OQ)5(BQ)2(H2O)] (3Sm), where BQ is 2,7′-biquinoline-8,8′-diolate, resulting from an unusual coupling reaction between two OQ/HOQ species at the 2 and 7′ positions. Complexes 1–3 and HOQ co-crystal 2·2HOQ were isolated as single crystals from separate reactions although formation of other products under the reaction conditions used was likely. Analogues of 3Sm with erbium and ytterbium were obtained using respective rare-earth metal filing in combination with nickel powder. Reaction involving cobalt powder only, without any rare-earth metals, yielded a homoleptic complex containing only the 8-quinolinolate ligand i.e. [Co4(OQ)8] (4). These results highlight the rewards, in terms of rich synthetic chemistry, and pitfalls, in terms of yield and isolation, of the pseudo-solid state synthetic approach using 8-quinolinolate ligands.

Synthesis characterization and hydroformylation activity of new mononuclear rhodium(I) compounds incorporated with polar-group functionalized phosphines

A first effort employing a range of polar-group functionalized phosphines (L 1 –L 7 ) to design mononuclear Rh(I) compounds of [Rh(quin-8-O)(CO)(L)] (quin-8-O = 8-hydroxy quinolate) is described. The reaction of a Rh(I) precursor [Rh(μ-Cl)(CO)2]2 with 8-hydroxyquinoline in the presence of a base followed by phosphines (L 1 –L 7 ) produced only a single isomer of [Rh(quin-8-O)(CO)(L)] compounds (1–7) with pendant, i.e. non-bonded, polar-groups (includes carboxyl, hydroxyl and formyl). A relationship between Δgd31P chemical shifts and the ν(C≡O) was derived to evaluate and explain the σ-donor properties of these phosphines with respect to the electronic properties of the polar groups and the extent of π-back-bonding to the CO group. These mononuclear Rh(I)-Phosphines were investigated as catalysts in the hydroformylation of 1-hexene and cyclohexene in aqueous two-phase and single-phase solvent systems. The Rh(I) catalysts with strong σ-donor and hydrophilic phosphines provided better yields and selectivities for the hydroformylation products, which is a reverse trend compared to literature reports. When the Rh(I) compounds contained strong σ-donor phosphines, the π-acceptor properties of the pyridine ring of 8-hydroxyquinolate were found to be beneficial for the facile cleavage of the CO group during hydroformylation, and additionally, to improve the kinetic stability of catalysts.

Surprisingly bright near-infrared luminescence and short radiative lifetimes of ytterbium in hetero-binuclear Yb-Na chelates

New heterobinuclear lanthanide complexes with benzoxazole-substituted 8-hydroxyquinolines, [Ln(ligand)(2)(mu-ligand)(2)Na] (Ln: Yb, Lu), have been prepared and their structure established by X-ray crystallography, (1)H NMR spectroscopy, and photophysical studies. The complexes display efficient ligand-sensitized near-infrared luminescence of ytterbium at 925-1075 nm with lifetimes and quantum yields as high as 22 micros and 3.7%, in the solid state, and 20 micros and 2.6% in CH(2)Cl(2) solution, respectively. These quantum yields are the highest reported to date for ytterbium complexes with organic ligands containing C-H bonds. A long-wavelength and intense intraligand charge-transfer transition (lambda(max) = 446-456 nm; epsilon approximately 1.2 x 10(4) M(-1) cm(-1)) allows for the excitation of infrared luminescence with visible light up to 600 nm. Remarkable features of these complexes include (i) quantitative ligand-to-Yb(III) energy transfer resulting in high overall efficiency of the ytterbium luminescence, (ii) unusually short radiative lifetime of the Yb(III) ion, 706-745 micros for solutions in CH(2)Cl(2), calculated from the f-f absorption spectra, and 513-635 micros estimated for solid state samples from quantum yield and lifetime data, and (iii) the unexpected large influence of second-sphere composition on the radiative lifetime of ytterbium.

Near-infrared emission from novel Tris(8-hydroxyquinolinate)lanthanide(III) complexes-functionalized mesoporous SBA-15

A novel mesoporous material covalently bonded with 8-hydroxyquinoline (HQ) was synthesized (designated as Q-SBA-15). The 5-formyl-8-hydroxyquinoline grafted to (3-aminopropyl)triethoxysilane, that is, alkoxysilane modified 8-hydroxyquinoline (Q-Si), was used as one of the precursors for the preparation of the Q-SBA-15 material. On the basis of the other function of the Q-Si of coordinating to lanthanide (Ln) ions, for the first time, the LnQ 3 complexes (Ln = Er, Nd, Yb) have been covalently bonded to the SBA-15 materials. The derivative materials, denoted as LnQ 3-SBA-15, were characterized by field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption, and fluorescence spectra. Upon excitation at the ligands absorption bands, all of these materials show the characteristic near-infrared (NIR) luminescence of the corresponding lanthanide ions through the intramolecular energy transfer from the ligands to the lanthanide ions. The NIR luminescence of these mesoporous materials was compared with that of the corresponding pure LnQ 3 complexes and discussed in detail.