Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

New layered cobalt oxyfluoride, Sr2CoO3F

The first Ruddlesden-Popper type layered cobalt oxyfluoride, Sr(2)CoO(3)F, has been synthesized under a pressure of 6 GPa at 1700 °C and shown to adopt a K(2)NiF(4)-type structure with distorted square pyramidal coordination around Co and with O/F disorder at the apical sites.     

Properties of novel gel particles with projections and preparations of composite particles with gold nanoparticles

Mono-dispersed gel particles with projections were prepared by dispersion polymerization with ethyleneglycol dimethacrylate and a polyethyleneglycol (PEG) block macro azo initiator in H₂O/ethanol solutions. The effects of molecular weight of PEG blocks and polymerization conditions on the morphology and some properties were examined for the gel particles. The diameters and the extent of coagulation were different with the polymerization conditions. Relatively large specific areas and large swelling ratio with H₂O were obtained, and these values were related with the polymerization conditions. By mixing the gel particles with gold nanoparticles in solutions, composite particles were formed, which were composed of gold nanoparticles adsorbed on the gel particles. Interaction between gold nanoparticles and reactive azo groups remained in the gel particles concerned for the formation of the composite particles.     

Incorporation of cationic electron donor of Ni-pyridyltetrathiafulvalene with anionic electron acceptor of polyoxometalate

A new salt-[Ni(II)(DMSO)(5)(TTFPy)](2)[α-SiW(12)O(40)] (1)-based on polyoxometalates was prepared by coordinating a cationic electron donor of pyridyltetrathiafulvalene (TTFPy) with Ni(II). Although the TTFPy molecule did not form a salt with the anionic α-[SiW(VI)(12)O(40)](4-) because of the weak charge-transfer (CT) interaction, the coordination of Ni with the pyridyl moiety permitted salt formation driven by electrostatic interaction, giving a single crystal of 1. Crystallographic analysis, UV-vis and IR spectroscopy and electrochemical characterization revealed that the fully oxidized α-[SiW(VI)(12)O(40)](4-) was crystallized with the neutral TTFPy moiety from the acetonitrile solution because of the low electron-withdrawing ability of α-[SiW(VI)(12)O(40)](4-), forming a brown-orange crystal. The crystal colour quickly turned to black by immersing in methanol, due to CT from TTF moiety to α-[SiW(VI)(12)O(40)](4-), which was caused by the solvent effect. Increase in the solvent acceptor number from 18.9 for acetonitrile to 41.3 for methanol resulted in the enhancement of the electron withdrawing ability of α-[SiW(VI)(12)O(40)](4-) by 0.317 V in methanol.     

Structural and electrical transport properties of FeH x under high pressures and low temperatures

We present the first successful in situ simultaneous measurement of the electrical resistance and X-ray diffraction of FeH _x (x～ 1) under high-pressure H₂ up to 25.5 GPa and low temperatures down to 9 K. The electrical resistivity ρ showed a sharp increase with the formation of iron-hydride FeH _x (x～ 1) at 3.5 GPa. The ?′-phase of FeH _x was found to be metallic up to 25.5 GPa. The ρ vs. T curves up to 16.5 GPa approximately follow Fermi-liquid law below 25 K. However, T ⁵ was found to be better fitting at 25.5 GPa. This change can be considered to be related to the previously reported ferromagnetism collapse at corresponding pressure.     

Experimental and theoretical evidence for pressure-induced metallization in FeO with rocksalt-type structure

Electrical conductivity of FeO was measured up to 141 GPa and 2480 K in a laser-heated diamond-anvil cell. The results show that rock-salt (B1) type structured FeO metallizes at around 70 GPa and 1900 K without any structural phase transition. We computed fully self-consistently the electronic structure and the electrical conductivity of B1 FeO as a function of pressure and temperature, and found that although insulating as expected at ambient condition, B1 FeO metallizes at high temperatures, consistent with experiments. The observed metallization is related to spin crossover.     

Synthesis and properties of novel extended BODIPYs with rigid skeletons

Novel extended BODIPYs fused with bicyclo rings were synthesized from bicyclopyrroles by combining Knoevenagel condensation, Suzuki coupling, and O-chelation. The absorption maxima of the BODIPYs ranged from the visible to near-infrared region and the compounds showed good solubility in organic solvents. The solubility of the bicycloBODIPY with 2-naphthyl groups at the α-position of the pyrrole units was particularly high. Heating converted distyrylBODIPY with bicyclo[2.2.2]octene to benzoBODIPY with absorption (748.5?nm) and fluorescence (775.0?nm) in the near-infrared region.     

Ferroelectric Behavior of a Hexamethylenetetramine‐Based Molecular Perovskite Structure

We report the development of a molecular ferroelectric material inspired by the hexamethylenetetramine (hmta) non‐centrosymmetric molecular rotator. The bromide salt of diprotonated hmta (hmtaH₂) crystalized as (hmtaH₂)(NH₄)Br₃ in a metal‐free ABX₃ perovskite‐type structure, in which the A and B sites are occupied by hmtaH₂²⁺ and ammonium cations, respectively. The compound crystallized in the Pma2 polar space group. A distorted polar perovskite structure formed owing to the distortion of {(NH₄)Br₆} octahedrons that are stabilized through the formation of NH???Br hydrogen bonds and the orientational ordering of positive charges on the non‐centrosymmetric hmtaH₂ molecules. This spontaneous polarization exhibited ferroelectric behavior with a nominally high Curie temperature (>400 K), in which the electrical switching of polarization originates from the rotation of the hmtaH₂ unit.     

Development of co-located 129Xe and 131Xe nuclear spin masers with external feedback scheme

We report on the operation of co-located ¹²⁹Xe and ¹³¹Xe nuclear spin masers with an external feedback scheme, and discuss the use of ¹³¹Xe as a comagnetometer in measurements of the ¹²⁹Xe spin precession frequency. By applying a correction based on the observed change in the ¹³¹Xe frequency, the frequency instability due to magnetic field and cell temperature drifts are eliminated by two orders of magnitude. The frequency precision of 6.2 μHz is obtained for a 10⁴ s averaging time, suggesting the possibility of future improvement to ≈ 1 nHz by improving the signal-to-noise ratio of the observation.