J. A. Paixão

Triple-q Octupolar Ordering in NpO2.

We report the results of resonant x-ray scattering experiments performed at the Np M(4,5) edges in NpO2. Below T(0)=25 K, the development of long-range order of Np electric quadrupoles is revealed by the growth of superlattice Bragg peaks. The polarization and azimuthal dependence of the intensity of the resonant peaks are well reproduced assuming anisotropic tensor susceptibility scattering from a triple-q(-->) longitudinal antiferroquadrupolar structure. Electric-quadrupole order in NpO2 could be driven by the ordering at T0 of magnetic octupoles of Gamma(5) symmetry, splitting the Np ground state quartet and leading to a singlet ground state with zero dipole-magnetic moment.

One-step synthesis of dipyrromethanes in water

In this communication we describe the first results of an efficient synthesis of β-free-dipyrromethanes in water. This new method affords very pure products in moderate to high yields, using a cheap, non-toxic, environment friendly solvent, in a one-step procedure from pyrrole and carbonyl compounds, needing little or no work up procedures.

Rhombohedral-to-orthorhombic transition and multiferroic properties of Dy-substituted BiFeO3

Investigation of crystal structure, ferroelectric, and magnetic properties of polycrystalline Bi1−xDyxFeO3 (0.1≤x≤0.2) samples was carried out. X-ray diffraction study revealed composition-driven rhombohedral-to-orthorhombic R3c→Pnma phase transition at x∼0.15. Both structural phases were found to coexist in a broad concentration range. Piezoresponse force microscopy found suppression of the parent ferroelectric phase upon dysprosium substitution. Magnetometric study confirmed that the A-site doping induces appearance of a weak ferromagnetic behavior. Both the ferroelectric and magnetic properties were shown to correlate with a structural evolution.

Structural and magnetic phase transitions in Bi1−x Pr x FeO3 perovskites

Crystal structure and physical properties of materials demonstrating simultaneous spin and electric dipole ordering have recently attracted much attention [1, 2]. The interest is explained by promising possibilities of exploitation of the intrinsic cross-coupling effects (induction of magnetization by an electric field or of electric polarization by a magnetic field) in practical applications. Most of the principal mechanisms underlying the combined ferroelectromagnetism in a single-phase compound [1] can be realized in complex oxides with the perovskite-like (ABO3) structure to make this class of materials one of the most popular from the viewpoint of multiferroic research. Among multiferroic perovskites, BiFeO3 is distinguished by its extremely high magnetic and ferroelectric transition temperatures (TN & 640 K, TC & 1100 K). In ferroelectric phase, the compound has a rhombohedrally distorted structure (space group R3c) [3] and possesses a large polarization PS * 100 lC/cm 2 [4] directed along the [001]h axis. Superexchange interactions between magnetically active Fe ions give rise to G-type antiferromagnetism. Due to the flexomagnetoelectric interaction [5], the antiferromagnetic structure is modulated with a long-range (*620 Å) cycloid [6]. The magnetic moments of iron ions retain their local antiferromagnetic G-type orientation and rotate along the propagation direction of the modulated wave in the plane perpendicular to the hexagonal basal plane. Such a modulation prevents the observation of weak ferromagnetism (allowed by symmetry of the space group R3c [7]) and of linear magnetoelectric effect [8]. The modulated structure can be suppressed by applying a strong magnetic field HC * 180–200 kOe to release a weak ferromagnetic moment of *0.25 emu/g [8]. Alternative effective way to suppress the spatial spin modulation is a lanthanide (Ln) A-site substitution [9]. Recognition of the possibility to tune and control multiferroic properties of bismuth ferrite via the ‘‘chemical pressure’’ motivated numerous investigations of Bi1-xLnxFeO3 solid solutions [10–13]. However, many early conclusions related to the structural phase evolution in these systems need to be carefully checked. A tendency to the structural phase separation characteristic of the materials [14] can hamper structural identification and can strongly influence the properties of the compounds under study. For instance, presence of a minor amount of the parent R3c phase can be a possible reason for the observation of ferroelectric-like behavior in the intrinsically nonferroelectric strongly-doped Bi1-xLnxFeO3 compounds [10]. These circumstances seem to underlie the scattering of the structural and ferroelectric data reported for BiFeO3-based compounds, so substituted BiFeO3 is still an area of fruitful research. Among Bi1-xLnxFeO3 series, praseodymium-containing system remains less well studied. Existing articles describe properties of Bi1-xPrxFeO3 multiferroics in a rather limited compositional range [15], reported data not always being consistent with some general trends observed in Bi1-xLnxFeO3 series [16]. To contribute to deeper understanding of the effect of Pr substitution on crystal structure V. A. Khomchenko (&) J. A. Paixão CEMDRX/Department of Physics, Faculty of Sciences and Technology, University of Coimbra, 3004-516 Coimbra, Portugal e-mail: uladzimir@fis.uc.pt

Magnetization Density in URhAl - Evidence For Hybridization Effects

URhAl is one of a large class of uranium compounds with the hexagonal ZrNiAl structure. It becomes ferromagnetic at 27 K and the ordered moment is found to be 0.94 mu B per formula unit. The authors have performed experiments with polarized neutrons in order to measure the magnetization density in the unit cell. A crystallographic study gives atomic positions in agreement with previous work, but they find that the crystals, which were grown by a Czochralski method, are highly perfect and exhibit a large amount of extinction. Corrections for these effects are discussed. The magnetization density shows that the total moment as measured by magnetization is made up of four contributions. The moments (in mu B) on uranium, RhI, RhII, and from the conduction electrons are, respectively 0.94(3), 0.28(2), 0.03(2), and -0.11(3). The observation of a large moment at the RhI site, which lies in the (001) plane with the U atoms shows that strong anisotropic hybridization occurs between the U and RhI. This is the cause of the very large bulk anisotropy. At the uranium site they have analysed the contributions from the spin and orbital moments and find - mu L/ mu S=1.81(7). The free ion 5f3 value for this ratio if 2.6. The reduction gives one a quantitative measure of hybridization in the system. The results are compared with those calculated from density functional theory.

Chiral 6,7-bis(hydroxymethyl)-1H,3H-pyrrolo[1,2-c]thiazoles with anti-breast cancer properties.

The synthesis and biological evaluation of 6,7-bis(hydroxymethyl)-1H,3H-pyrrolo[1,2-c]thiazoles as anticancer agents against MCF7 breast cancer cell lines is reported. The design of the new compounds has been guided considering (3R)-6,7-bis(hydroxymethyl)-5-methyl-3-phenyl-1H,3H-pyrrolo[1,2-c]thiazole as the lead compound due to its good performance against MCF7 breast cancer cell lines (IC(50) = 1.0 μM). The structural changes included the removal of the phenyl group at C-3, the replacement of this group by a 3,4,5-trimethoxyphenyl group, the removal of the methyl group at C-5 from the lead scaffold and the replacement of this group by a phenyl substituent. Overall, these studies showed that the combined presence of a phenyl group at C-3 and a methyl group at C-5 in the 1H,3H-pyrrolo[1,2-c]thiazole ring system is essential to ensure high cytotoxicty against MCF7 breast cancer cell lines. To probe whether the absolute configuration of the lead compound might affect the anticancer activity, its enantiomer was prepared and the activity against MCF7 cells was evaluated. (3S)-6,7-Bis(hydroxymethyl)-5-methyl-3-phenyl-1H,3H-pyrrolo[1,2-c]thiazole proved to be the most active compound so far studied, with IC(50) value of 0.5 μM.

Pyrrolidine-based amino alcohols: novel ligands for the enantioselective alkylation of benzaldehyde

A series of easily obtained pyrrolidine-based -amino alcohols derived from tartaric acid and primary amines was synthesized and used as chiral ligands in the enantioselective alkylation of benzaldehyde. Using diethylzinc, 1-phenyl-1-propanol was obtained with enantiomeric excesses of up to 80% when (3S,4S)-N-(1-naphthylmethyl)-3,4-dihydroxypyrrolidine was used. The nature of the N-substituent on the ligand, as well as the reaction temperature proved to significantly influence reaction product distribution as well as the enantiomeric excess of the chiral alcohol.

Composition- and temperature-driven structural transitions in Bi1−xCaxFeO3 multiferroics: a neutron diffraction study

Neutron powder diffraction and magnetization measurements of the Bi(1-x)Ca(x)FeO3 (0.05 ≤ x ≤ 0.14) compounds were carried out to follow the effect of the heterovalent A-site doping on the long-range structure and magnetic properties of the BiFeO3 multiferroic. Ca substitution induces the appearance of weak ferromagnetism in the initial ferroelectric R3c phase, but modifies the picture of polar displacements, so the average PbZrO3-like antiferroelectric structure is stabilized at x = 0.11. Further increase of the Ca content leads to transformation of the antipolar ionic shifts to give rise to the Pbam → Imma transition near x = 0.14. A structural study performed for the x = 0.05 compound at high temperature revealed the R3c → Pnma phase transition at 950 K. For x = 0.1 samples, an intermediate heating-induced structure separating the R3c and Pnma phases was found.

Novel erbium(III) complexes with 2,6-dimethyl-3,5-heptanedione and different N,N-donor ligands for ormosil and PMMA matrices doping

Three novel complexes, [Er(dmh)3(bipy)], [Er(dmh)3bath] and [Er(dmh)3(5NO2phen)], with 2,6-dimethyl-3,5-heptanedione (Hdmh) as the main sensitizer and either 2,2′-bipyridine (bipy), bathophenanthroline (bath) or 5-nitro-1,10-phenanthroline (5NO2phen) as synergistic ligands were synthesized. Upon excitation at the maximum absorption of the ligands, the complexes show the characteristic near-infrared (NIR) luminescence of the Er3+ ions, due to efficient energy transfer from the ligands to the central Er3+ ion via the antenna effect. Single crystals were grown and their structures were determined showing different Er–N distances. The compound with shorter Er–N distances, [Er(dmh)3(5NO2phen)], was found to be the best light harvester and the best for transferring the energy to the lanthanide among the three studied compounds. Finally, the novel complexes have been assessed for their application in sol–gel and polymer-based waveguides and optical amplifiers through their inclusion into ormosil and polymethylmethacrylate matrices. The dispersion was successful in the bipy and 5NO2phen cases, with the properties of the hybrid materials mimicking those of the pure complexes.

Substitution-driven structural and magnetic phase transitions in Bi0.86(La, Sm)0.14FeO3 system

Solid-state synthesis and investigation of crystal structure and magnetic properties of Bi0.86La0.14−xSmxFeO3 (0 ≤ x ≤ 0.14) ceramics were performed. It was found that a rhombohedral to orthorhombic phase transition took place in the series with decreasing average ionic radius of the substituting elements occupying the A-site of the ABO3 perovskite. Magnetic properties of the compounds were shown to correlate with evolution of their structural state. Pure rhombohedral samples 0 ≤ x ≤ 0.06 were obtained in a mixed antiferromagnetic/weak ferromagnetic state. A small residual magnetization characteristic of the compounds was found to weakly depend on change of the chemical composition. Progressive increase of the residual magnetization was observed upon the rhombohedral-to-orthorhombic transition. Reasons for the appearance of the weak ferromagnetism in orthorhombic and rhombohedral phases of the Bi0.86(La, Sm)0.14FeO3 compounds were analysed.