Liquid Crystalline Complexes of Cu(II) and Pd(II) with Ferrocene-Containing Ligands

The new liquid crystalline heteronuclear complexes Cu(II) 1a and Pd(II) 1b with a non-mesogenic ferrocene-containing β-enaminoketone L1 of the formula C5H5FeC5H4-C6H 4-NH-C2H2-(CO)-C6H 4OC12H25, showing monotropic nematic and smectic A phases, are studied. The ortho-palladated Cl-bridged dimeric complex 3 with a non-mesogenic ferrocene-containing Schiffs base L2 of the formula C5H5FeC5H4-C6H 4-N=CH-C6H4OC10H21, forming a stable smectic A phase, has been synthesized. The novel mixed-ligand heteronuclear complexes 4-7 have been obtained by treatment of the ortho-palladated complex 3 with appropriate ligands. Some of the resulting products exhibit the rather low-melting (below 100deg;C) smectic A phases. Structures of the compounds are studied by elemental analysis, 1H and 13C NMR, and ESR spectroscopies

Conformations of 1,5-Dihydro-3,7,8-trimethyl-2,4-benzodithiepine in Various Solvents and in the Solid Phase. NMR Data

13C CP/RMA spectroscopy was used to show that solid 1,5-dihydro-3,7,8-trimethyl-2,4-benzodithiepine exists in a boat-e conformation

Direct spectroscopic observation of the atomic-scale mechanisms of clustering and homogenization of rare-earth dopant ions in vitreous silica

Structural aspects of clustering of rare earth ions in oxide glasses have been studied for the last several years in relation to their applications in photonics. However, the mechanism of homogenization of the spatial distribution of rare earth ions by codoping, typically with Al or P, is still not well understood. In this work we report direct experimental determination of the homogenization mechanism of Yb3+ ion clusters in silica glasses doped with 0.1 wt. % Yb2 O3 and codoped with Al or P, using two-dimensional HYSCORE-EPR spectroscopy. The results lead us to conclude that Yb creates its coordination environment via formation of Yb-O-Si and Yb-O-Yb bonds in a Yb-doped silica glass and even the light codoping with Al starts replacing these bonds with Yb-O-Al linkages. Heavy codoping with P replaces all Yb-O-Si Yb linkages with Yb-O-P linkages. The formation of a next-nearest neighbor shell of Al or P creates suitable structural pockets, which ultimately leads to homogenization. © 2006 The American Physical Society

Liquid-crystalline CuII and PdII complexes with nonmesogenic ferrocene-containing β-aminovinyl ketone

New liquid-crystalline heteropolynuclear complexes L2M (M = Cu2+ (2a), Pd2+ (2b)) were synthesized by the reactions of C5H5FeC5H4-C6H4NH-C2H2-(CO)-C6H4OC12H25 (1, LH) with copper(II) and palladium(II) acetates. Compound 2b was found to possess monotropic nematic and smectic phases; 2a exhibits the monotropic nematic phase and a phenomenon of "double melting." The compositions and structures of compounds 1 and 2a,b were established by elemental analysis, 1H and 13C NMR, ESR, and IR spectroscopy

Microwave resonant technique in studies of photodielectric properties of bulk, thin film and nanoparticle materials

© 2016 IOP Publishing Ltd Printed in the UK.An enhanced contactless microwave technique allows us to study the photoconductivity of materials. The transient response of the complex permittivity of matter (ϵ = ϵ1 - jϵ 2) under optical irradiation is measured with nanosecond time resolution. The main advantage of the novel methodology is the elimination of the polarization effect in evaluating photoconductivity. The potential of the methodology was demonstrated by photoconductivity measurements in Si [1 0 0] crystal, CeO2 nanocrystalline powder and Ce-doped LiYF4 single crystal. The variations of complex permittivity (δϵ1 and δϵ 2) of Si [1 0 0] crystal, CeO2 nanocrystalline powder and Ce-doped LiYF4 single crystal under optical irradiation was measured and accurate values for crystalline band gaps were extracted. Finally, quantum confinement effects were observed in nano-size crystalline powders

The Jahn-Teller effect in Cr5+-doped PbTiO3: A multi-frequency electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti4+ sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400K at 9GHz (X), 34GHz (Q) and 94GHz (W band). The Jahn-Teller effect stabilizes the vibronic ground state of the 3d1 electron of the Cr5+ ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti-or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr5+O6 12- are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200K. © 2010 IOP Publishing Ltd

EPR Evidence of Unusual Dopant Valency States in Nanocrystalline Er-doped CeO<inf>2</inf>

© 2015, Springer-Verlag Wien. The structure and oxidation state of the Er dopant cation in CeO2 single crystal and nanocrystals with size ranging from 22 to 300 nm are studied using electron paramagnetic resonance (EPR) spectroscopy at X- and at Q-band near liquid-He temperatures. Besides the expected EPR line due to Er3+ in cubic sites in the lattice, unusual EPR lines with g values around 14 and 20 are observed in nanocrystalline CeO2. The appearance of these lines suggests the formation of non-Kramers Er2+, Er4+ ions, which becomes increasing favorable with decreasing nanoparticle size. Formation of rare earth ions with such unusual oxidation states in nanoparticles can be exploited in tuning their catalytic activity and optical properties