Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet

The reactivity of the new flexible potentially pentadentate N₃O₂ aminophenol ligand H₄L^r (2,2'-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H₄L^r with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy₄(H₂L^r)₃(Cl)₄(μ₃-O)(EtOH)₂(H₂O)₂]·2EtOH·H₂O (1·2EtOH·H₂O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy₅(H₂L^r)₂(H_2.5L^r)₂(NO₃)₄(µ₃-O₂)₂]·2H₂O (2·2H₂O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho₂(H₂L^r)(H₃L^r)(NO₃)₂(H₂O)₂](NO₃)} 2.5H₂O (3·2.5H₂O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy₄ and Ho₂ complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2·2H₂O is a single molecule magnet, with an U_eff barrier of 61.2 K (43.2 cm^-1). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date.

Pushing the boundary of covalency in lanthanoid-tellurium bonds: Insights from synthesis, molecular and electronic structures of low-coordinate, monomeric europium(II) and ytterbium(II) tellurolates

Owing to the strict hard/soft dichotomy between the lanthanoids and tellurium atoms, and the strong affinity of lanthanoid ions for high coordination numbers, low-coordinate, monomeric lanthanoid tellurolate complexes have remained elusive as compared to the lanthanoid complexes with lighter group 16 elements (O, S, and Se). This makes the development of suitable ligand systems for low-coordinate, monomeric lanthanoid tellurolate complexes an appealing endeavor. In a first report, a series of low-coordinate, monomeric lanthanoid (Yb, Eu) tellurolate complexes were synthesized by utilizing the secondary bonding interaction stabilized hybrid organotellurolate ligands. The reaction of bis[2-((dimethylamino)methyl)phenyl] ditelluride, 1 and 8,8'-diquinolinyl ditelluride, 2 with Ln0 metal (Ln = Eu, Yb) resulted in the formation of monomeric complexes [LnII(TeR)2(Solv)2] [R = C6H4(CH2NMe2)-2] [3: Ln = Eu, Solv = tetrahydrofuran; 4: Ln = Eu, Solv = acetonitrile; 5: Ln = Yb, Solv = tetrahydrofuran; 6: Ln = Yb, Solv = pyridine] and [EuII(TeNC9H6)2(Solv)n] (7: Solv = tetrahydrofuran, n = 3; 8: Solv = 1,2-dimethoxyethane, n = 2), respectively. Complexes 3-4 and 7-8 represent the first sets of examples of monomeric europium tellurolate complexes. The molecular structures of complexes 3-8 are validated by single-crystal X-ray diffraction studies.

Luminescent Complexes of Europium (III) with 2-(Phenylethynyl)-1,10-phenanthroline: The Role of the Counterions

New antenna ligand, 2-(phenylethynyl)-1,10-phenanthroline (PEP), and its luminescent Eu (III) complexes, Eu(PEP)₂Cl₃ and Eu(PEP)₂(NO₃)₃, are synthesized and characterized. The synthetic procedure applied is based on reacting of europium salts with ligand in hot acetonitrile solutions in molar ratio 1 to 2. The structure of the complexes is refined by X-ray diffraction based on the single crystals obtained. The compounds [Eu(PEP)₂Cl₃]·2CH₃CN and [Eu(PEP)₂(NO₃)₃]∙2CH₃CN crystalize in monoclinic space group P2_1/n and P2_1/c, respectively, with two acetonitrile solvent molecules. Intra- and inter-ligand π-π stacking interactions are present in solid stat and are realized between the phenanthroline moieties, as well as between the substituents and the phenanthroline units. The optical properties of the complexes are investigated in solid state, acetonitrile and dichloromethane solution. Both compounds exhibit bright red luminescence caused by the organic ligand acting as antenna for sensitization of Eu (III) emission. The newly designed complexes differ in counter ions in the inner coordination sphere, which allows exploring their influence on the stability, molecular and supramolecular structure, fluorescent properties and symmetry of the Eu (III) ion. In addition, molecular simulations are performed in order to explain the observed experimental behavior of the complexes. The discovered structure-properties relationships give insight on the role of the counter ions in the molecular design of new Eu (III) based luminescent materials.

Lanthanoid Complexes as Molecular Materials: The Redox Approach

The development of molecular materials with novel functionality offers promise for technological innovation. Switchable molecules that incorporate redox-active components are enticing candidate compounds due to their potential for electronic manipulation. Lanthanoid metals are most prevalent in their trivalent state and usually redox-activity in lanthanoid complexes is restricted to the ligand. The unique electronic and physical properties of lanthanoid ions have been exploited for various applications, including in magnetic and luminescent materials as well as in catalysis. Lanthanoid complexes are also promising for applications reliant on switchability, where the physical properties can be modulated by varying the oxidation state of a coordinated ligand. Lanthanoid-based redox activity is also possible, encompassing both divalent and tetravalent metal oxidation states. Thus, utilization of redox-active lanthanoid metals offers an attractive opportunity to further expand the capabilities of molecular materials. This review surveys both ligand and lanthanoid centered redox-activity in pre-existing molecular systems, including tuning of lanthanoid magnetic and photophysical properties by modulating the redox states of coordinated ligands. Ultimately the combination of redox-activity at both ligands and metal centers in the same molecule can afford novel electronic structures and physical properties, including multiconfigurational electronic states and valence tautomerism. Further targeted exploration of these features is clearly warranted, both to enhance understanding of the underlying fundamental chemistry, and for the generation of a potentially important new class of molecular material.

High Refractive-Index Hybrids Consisting of Water-Soluble Matrices with Bipyridine-Modified Polyhedral Oligomeric Silsesquioxane and Lanthanoid Cations

We report high refractive-index (RI) films composed of polyhedral oligomeric silsesquioxane (SSQ) matrices and various lanthanoid cations. The SSQ matrices were constructed from octaammonium SSQ by connecting with bipyridine dicarboxylic acid, which is expected to capture cations. By modulating the feed ratio between SSQ and dicarboxylic acid, the series of the SSQ matrices were obtained with variable cross-linking ratios among the SSQ units. Thin transparent films were able to be prepared through the drop-casting method with the aqueous mixtures containing SSQ matrices and various kinds of lanthanoid salts up to 40 wt %. From RI measurements, it was revealed that the increase of the amount of the metal ion can significantly lift up the RI values. In particular, critical losses of Abbe numbers, which theoretically have the trade-off relationship toward increases in RI values, were hardly detected. This effect could be obtained by cation assembly in local spots that are assisted by SSQ.

Luminescent Lanthanoid Calixarene Complexes and Materials

This review aims to provide an overview of recent examples of lanthanoid-calixarene complexes incorporated into light-emitting materials. Background information on the antenna effect and early work on lanthanoid complexes on calixarenes is provided to set the context. Classes of materials discussed include polymers, nanoparticles, and metal clusters.

[Composition Characteristics and Sources Apportionment of Lanthanoid in PM2.5 of Quanzhou]

Samples of PM_2.5 were collected from 5 sites in Quanzhou in March, April and July, 2014. The concentrations of lanthanoid and other trace metals in the PM_2.5 were determined by Inductively Coupled Plasma Mass Spectrometry(ICP-MS). The total lanthanoid concentration (ΣLoid), the ratio of light-lanthanoid(L Loid, including, La, Ce, Pr, Nd, Sm and Eu) to heavy-lanthanoid(H Loid, including Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in PM_2.5 were 2.490-5.708 ng·m^-3(65.682-126.529 μg·g^-1) and 12.086-14.319, respectively. The distribution pattern of Loid in PM_2.5 was also evaluated in this study. All PM_2.5 samples showed similar distribution pattern with local topsoil. And positive Ce and negative Eu anomalies were observed in PM_2.5. La-Ce-V plots and chemical mass balance(CMB) model were used for source identification and apportionment of PM_2.5in Quanzhou. The CMB model was used to identify four main sources:urban fugitive dust, coal combustion, vehicle exhaust and waste incineration emission which had a contribution of 18.9%, 10.9%, 30.6% and 30.2%, respectively.

Characterization of Nonanuclear Europium and Gadolinium Complexes by Gas-Phase Luminescence Spectroscopy

Gas-phase measurements using mass-spectrometric techniques allow determination of the luminescence properties of selected molecular systems with knowledge of their exact composition. Furthermore, isolated luminophores are unaffected by matrix effects like solvent interactions or crystal packing. As a result, the system complexity is reduced relative to the condensed phase and a direct comparison with theory is facilitated. Herein, we report the intrinsic luminescence properties of nonanuclear europium(III) and gadolinium(III) 9-hydroxyphenalen-1-one (HPLN)-hydroxo complexes. Luminescence spectra of [Eu9(PLN)16(OH)10](+) ions reveal an europium-centered emission dominated by a 4-fold split Eu(III) hypersensitive transition. The corresponding Gd(III) complex, [Gd9(PLN)16(OH)10](+), shows a broad emission from a ligand based triplet state with an onset of about 1000 wavenumbers in excess of the europium emission. As supported by photoluminescence lifetime measurements for both complexes, we deduce an efficient europium sensitization via PLN-based triplet states. The luminescence spectra of the complexes are discussed in terms of a square antiprismatic europium/gadolinium core structure as suggested by density functional computations.

Optimizing contrast agents with respect to reducing beam hardening in nonmedical X-ray computed tomography experiments

Iodine is commonly used as a contrast agent in nonmedical science and engineering, for example, to visualize Darcy flow in porous geological media using X-ray computed tomography (CT). Undesirable beam hardening artifacts occur when a polychromatic X-ray source is used, which makes the quantitative analysis of CT images difficult. To optimize the chemistry of a contrast agent in terms of the beam hardening reduction, we performed computer simulations and generated synthetic CT images of a homogeneous cylindrical sand-pack (diameter, 28 or 56 mm; porosity, 39 vol.% saturated with aqueous suspensions of heavy elements assuming the use of a polychromatic medical CT scanner. The degree of cupping derived from the beam hardening was assessed using the reconstructed CT images to find the chemistry of the suspension that induced the least cupping. The results showed that (i) the degree of cupping depended on the position of the K absorption edge of the heavy element relative to peak of the polychromatic incident X-ray spectrum, (ii) (53)I was not an ideal contrast agent because it causes marked cupping, and (iii) a single element much heavier than (53)I ((64)Gd to (79)Au) reduced the cupping artifact significantly, and a four-heavy-element mixture of elements from (64)Gd to (79)Au reduced the artifact most significantly.

A multimineral natural product from red marine algae reduces colon polyp formation in C57BL/6 mice

The goal of this study was to determine if a multimineral natural product derived from red marine algae could reduce colon polyp formation in mice on a high-fat diet. C57BL/6 mice were maintained for up to 18 mo either on a high-fat "Western-style" diet or on a low-fat diet (AIN 76A), with or without the multimineral-supplement. To summarize, colon polyps were detected in 22 of 70 mice (31%) on the high-fat diet but in only 2 of 70 mice (3%) receiving the mineral-supplemented high-fat diet (P < 0.0001). Colon polyps were detected in 16 of 70 mice (23%) in the low-fat group; not significantly different from high-fat group but significantly higher than the high-fat-supplemented group (P = 0.0006). This was in spite of the fact that the calcium level in the low-fat diet was comparable to the level of calcium in the high-fat diet containing the multimineral-product. Supplementation of the low-fat diet reduced the incidence to 8 of 70 mice (11% incidence). Taken together, these findings demonstrate that a multimineral natural product can protect mice on a high-fat diet against adenomatous polyp formation in the colon. These data suggest that increased calcium alone is insufficient to explain the lower incidence of colon polyps.