Physics of Polymorphic Transitions in CeRuSn

We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of X-ray diffraction experiments conducted at 300, 275 and 120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present X-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (290 K) and than to a triple CeCoAl superstructure at 225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of the transition in elementary Cerium, suggesting that similar physics, i.e., a Kondo influenced transition and strong lattice vibrations might be the driving forces

Norleucine, a natural occurrence in a novel ergot alkaloid γ-ergokryptinine

A novel natural peptide ergot alkaloid γ-ergokryptinine containing norleucine has been isolated from ergot sclerotia of the field-growing parasitic fungus Claviceps purpurea CCM 8059. Its structure was deduced from the NMR and mass spectral data. The final structural proof was provided by the crystal structure determination, which is the first X-ray structure of a natural Nle-containing secondary metabolite. The conformations of three ergopeptinines: γ-ergokryptinine, ergoladinine, and α-ergokryptinine were compared. © Springer-Verlag 2005

Neočekávaná reakce derivátů closo-thiadodekaboranu s fenylmagnesium bromidem

Derivatives of closo-thiadodecaborane, closo-SB11H11, undergo an unexpected hydrogen substitution under reaction with phenylmagnesium bromide

CZECHIA. Critical junctures in the media transformation process.

There are several critical junctures that arise from the context of the social, political, economic, and technological developments within the media in Czechia between 2000 and 2020. We identify these seven: (1) the consequences of the social transformation after 1989, which lasted until the beginning of the 21st century; (2) the emergence of new media, whose production and user development occurred mainly after the year 2000; (3) the economic crisis in 2008; (4) the emergence of new political movements after 2011; (5) the refugee crisis in 2015; (6) the polarisation of society; and (7) the pandemic of Covid-19 as a complex phenomenon after 2019. With focus on the agency of different actors in propelling certain risks and opportunities at the outlined critical junctures, these are the groups with either specific knowledge of the Czech media development or with a long professional history: (1) media industry representatives (e.g., media owners, media managers, journalists, journalists’ professional unions); (2) communication researchers and lecturers; (3) media analysts and analytical companies; and (4) NGOs. As shown by our analysis of the Czech media system between 2000 and 2020, the critical junctures, risks, and opportunities, have not contributed to the development of deliberative communication and democracy in Czechia. On the contrary, we conclude that the changes just after 2000 led to an illiberal turn that stems from the social, political, economic, and technological development of both society and the media system

Magnetic Properties of a Novel CeCo0.715Si2.285CeCo_{0.715}Si_{2.285} Compound

We report on the basic physical properties of a novel $CeCo_{0.715}Si_{2.285}$ compound, mainly its rich magnetic phase diagram. The compound crystallizes in the I-4m2 space group structure with extremely elongated unit cell (a = 4.12 Å, c = 32.84 Å). In a zero magnetic field it orders antiferromagnetically at $T_{N}$ = 10.5 K with another order-to-order transition at 9.5 K. Under application of a magnetic field along the c-axis it manifests numerous magnetic transitions in small fields (B < 500 mT), resembling the so-called "devil's staircase" systems. Above 1 T the magnetization is almost constant up to 14 T (maximum magnetic field applied within our study) but considerably reduced (0.3 $μ_B$/Ce) with respect to the free $Ce^{3+}$ ion. After removing the applied field, however, the high field state remains unchanged to be removed in negative fields. The compound also exhibits strong hysteresis of magnetization with respect to varying temperature or magnetic field. For fields applied along the a-axis typical behavior for the hard axis in the material with uniaxial anisotropy is observed

Structure and Magnetic Properties of Three-Dimensional Gadolinium-Based Hybrid Framework

In the present work we have focused on the preparation and magnetic study of coordination polymer formed by Gd(III) cations as nodes and formate (HCOO¯; FOR) anions as charge compensating linkers. The prepared complex with formula ${[Gd(μ_{3}-FOR)_{3}]}_{n}$ was characterized by single-crystal X-ray diffraction, and high-energy powder X-ray diffraction. The structural study showed that complex is formed by 3D polymeric network with the shortest Gd-Gd, distances of 3.998 Å. The magnetic properties of the complex were studied by magnetic susceptibility $χ_{M}(T)$ and magnetization M(H) measurements. The results show on the weak antiferromagnetic coupling at low temperatures represented by the Weiss constant θ=-0.468 K. The value of effective magnetic moment $μ_{eff}=7.57μ_{B}$, which was estimated from the experimental data is close to the theoretical value for systems with S=7/2. Correlation between crystal structure of complexes and magnetic properties is presented

Redox-switchable α-diimine palladium catalysts for control of polyethylene topology

A series of palladium complexes bearing ferrocene substituted α-diimine ligands was synthesized and investigated for ethene polymerization at different conditions to modulate the extent of “chain-walking” mechanism and regulate branching and topology of resulting polyethylenes. All ferrocene substituted complexes catalyzed living/controlled ethene polymerization. The ability of ferrocene substituted palladium complexes to provide polyethylenes with dendritic topology was proved by measuring their Mark-Houwink plots. In-situ chemical oxidation of ferrocene moieties via silver triflate was used to affect the catalyst electronic structure and support the “chain-walking” mechanism. Oxidation of palladium catalyst led to its destabilization while the catalytic activity of newly formed sites was substantially increased. It was demonstrated that catalyst oxidation is a powerful tool to regulate the topology of resulting polyethylenes

Mechanical vs Electronic Strain: Oval-Shaped Alkynyl-Pt(II)-Phosphine Macrocycles

Pyridine-terminated molecular rods and either (i) the cis-(dppp)(I)Pt(CC-triptycene-CC)Pt(I)(dppp) rod or (ii) the trans-(PEt3)2(I)Pt(CC-biphenyl-CC)Pt(I)(PEt3)2 rod assemble into macrocycles, characterized by NMR, ESI-IMS, and in two cases also single-crystal X-ray diffraction. The former form rectangles with bidentate phosphine-containing cis-coordinated Pt(II)-alkyne corners. In the latter, the preference of the Pt centers for a trans configuration overrules the preference of the triple bonds for linearity and NMR shows that they have oval structures with alternating bent rod and bent trans (CC)Pt(PEt3)2(CC) components, in agreement with density functional theory calculations

Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy

This paper reports results of a study aimed at understanding the precipitation processes occurring during the annealing of two Al-Sc-Zr-based alloys with and without Mn prepared by powder metallurgy with subsequent hot extrusion at 350°C. Samples were isochronally annealed up to ≈ 570°C. Precipitation behaviour was studied by electrical resistometry and differential scanning calorimetry. Mechanical properties were monitored by microhardness HV1 measurements. Transmission electron microscopy examinations and X-ray diffraction of specimens quenched from temperatures of significant resistivity changes helped to identify the microstructural processes responsible for these changes. Fine (sub)grain structure develops and fine coherent $Al_3Sc$ and/or $Al_3(Sc,Zr)$ particles precipitate during extrusion in both alloys. The distinct changes in resistivity (at temperatures above ≈ 330°C) of the Al-Mn-Sc-Zr alloy are mainly caused by precipitation of Mn-containing particles. The easier diffusion of Mn atoms along the (sub)grain boundaries is responsible for the precipitation of the $Al_6Mn$ and/or $Al_6(Mn,Fe)$ particles at relatively lower temperatures compared to the temperature range of precipitation of these particles in the classical mould-cast Al-Mn-Sc-Zr alloys The apparent activation energy for precipitation of the $Al_3Sc$ and $Al_6Mn$ particles in the Al-Mn-Sc-Zr alloy was determined as (106 ± 10) kJ $mol^{-1}$ and (152 ± 33) kJ $mol^{-1}$, respectively

Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy

This paper reports results of a study aimed at understanding the precipitation processes occurring during the annealing of two Al-Sc-Zr-based alloys with and without Mn prepared by powder metallurgy with subsequent hot extrusion at 350°C. Samples were isochronally annealed up to ≈ 570°C. Precipitation behaviour was studied by electrical resistometry and differential scanning calorimetry. Mechanical properties were monitored by microhardness HV1 measurements. Transmission electron microscopy examinations and X-ray diffraction of specimens quenched from temperatures of significant resistivity changes helped to identify the microstructural processes responsible for these changes. Fine (sub)grain structure develops and fine coherent $Al_3Sc$ and/or $Al_3(Sc,Zr)$ particles precipitate during extrusion in both alloys. The distinct changes in resistivity (at temperatures above ≈ 330°C) of the Al-Mn-Sc-Zr alloy are mainly caused by precipitation of Mn-containing particles. The easier diffusion of Mn atoms along the (sub)grain boundaries is responsible for the precipitation of the $Al_6Mn$ and/or $Al_6(Mn,Fe)$ particles at relatively lower temperatures compared to the temperature range of precipitation of these particles in the classical mould-cast Al-Mn-Sc-Zr alloys The apparent activation energy for precipitation of the $Al_3Sc$ and $Al_6Mn$ particles in the Al-Mn-Sc-Zr alloy was determined as (106 ± 10) kJ $mol^{-1}$ and (152 ± 33) kJ $mol^{-1}$, respectively