Homo- and heteroleptic lanthanide-iron alkoxides as precursors in materials synthesis

Bimetallic iron-lanthanide alkoxides were synthesized by reacting [Ln{N(SiMe₃)₂}₃] (Ln ?= ?Pr, Nd, Er) with [Fe₂(O^tBu)₆] in excess tert-butyl alcohol that triggered in-situ ligand exchange and Lewis acid-base interactions to form heterometallic compounds. Single crystal X-ray diffraction analyses of new compounds demonstrated that both Nd and Er containing compounds resulted in the formation of a hetero-bimetallic framework based on 1:1 Ln:Fe ratio, whereas higher Fe ratio (1:2) was observed when Pr was used as the rare earth metal, possibly due to its larger ionic radius (Pr(III): 0.99 ?Å). When the reaction was performed in the presence of chelating ligands (L: H-tfb-mea ?= ?N-(4,4,4-trifluorobut-1-en-3-on)-methoxyethyleneamine; H₂-tfb-en ?= ?N–N′-bis-(4,4,4-trifluorobut-1-en-3-on)-ethylenediamine), heteroleptic Ln-Fe derivatives were formed that were used in a representative case ([NdFe(L)(O^tBu)_m(HO^tBu)]) as efficient precursor to synthesize nanocrystalline NdFeO₃ ceramic.     

CO2 Separation by Imide/Imine Organic Cages

Two novel imide/imine-based organic cages have been prepared and studied as materials for the selective separation of CO₂ from N₂ and CH₄ under vacuum swing adsorption conditions. Gas adsorption on the new compounds showed selectivity for CO₂ over N₂ and CH₄. The cages were also tested as fillers in mixed-matrix membranes for gas separation. Dense and robust membranes were obtained by loading the cages in either Matrimid® or PEEK-WC polymers. Improved gas-transport properties and selectivity for CO₂ were achieved compared to the neat polymer membranes.     

Hydrogen Bonding and Vaporization Thermodynamics in Hexafluoroisopropanol-Acetone and -Methanol Mixtures. A Joined Cluster Analysis and Molecular Dynamic Study

Binary mixtures of hexafluoroisopropanol with either methanol or acetone are analyzed via classical molecular dynamics simulations and quantum cluster equilibrium calculations. In particular, their populations and thermodynamic properties are investigated with the binary quantum cluster equilibrium method, using our in-house code Peacemaker 2.8, upgraded with temperature-dependent parameters. A novel approach, where the final density from classical molecular dynamics, has been used to generate the necessary reference isobars. The hydrogen bond network in both type of mixtures at molar fraction of hexafluoroisopropanol of 0.2, 0.5, and 0.8 respectively is investigated via the molecular dynamics trajectories and the cluster results. In particular, the populations show that mixed clusters are preferred in both systems even at 0.2 molar fractions of hexafluoroisopropanol. Enthalpies and entropies of vaporization are calculated for the neat and mixed systems and found to be in good agreement with experimental values.     

Quantum holonomy theory and hilbert space representations

We present a new formulation of quantum holonomy theory, which is a candidate for a non‐perturbative and background independent theory of quantum gravity coupled to matter and gauge degrees of freedom. The new formulation is based on a Hilbert space representation of the algebra, which is generated by holonomy‐diffeomorphisms on a 3‐dimensional manifold and by canonical translation operators on the underlying configuration space over which the holonomy‐diffeomorphisms form a non‐commutative ‐algebra. A proof that the state that generates the representation exist is left for later publications.     

Cryogenic Permanent Magnet Undulator Development at HZB/BESSY II

The costs of a synchrotron radiation facility scales approximately linearly with the length (FEL) or the circumference (storage ring) of the machine. It is always beneficial for the reduction in overall expenses to utilize short period in-vacuum undulators (IVUs) for X-ray production. This is the reason for the success of the IVU development which was started almost 20 years ago in Japan [1 T. Hara, J. Synch. Rad., 5, 403–405 (1998).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–3 T. Tanaka, Proc. FEL Conf., Stanford, CA, 370–377 (2005). [Google Scholar]]. Today, IVUs are implemented into nearly all third-generation storage rings. Ten years ago, the concept of cryogenically cooled permanent magnet undulators (CPMUs) was proposed [4 T. Hara, Phys. Rev. ST Accel. Beams, 7, 050702-1-6 (2004).[Crossref] , [Google Scholar]]. The magnetic properties of rare earth magnets (i.e., the remanence and the coercivity) improve substantially at low temperatures. The remanence increases by about 15%, whereas the coercivity grows by a factor of three to four. Due to the performance gain and the low technical risk of CPMUs, such devices are under development all over the world. The first generation of CPMUs, with period lengths well below 20 mm, is successfully operated at ESRF [5 J. Chavanne, AIP Conf. Proc., SRI 2009, Melbourne, Australia 1234, 25–28 (2010). [Google Scholar], 6 J. Chavanne, Proc. PAC, Vancouver, BC, Canada, 2414–2416 (2009). [Google Scholar]], PSI [7 T. Tanaka et al, Phys. Rev. ST Accel. Beams, 12, 120702-1-5 (2009).[Crossref] , [Google Scholar]], DIAMOND [8 C. Ostenfeld and M. Pedersen, Proc. IPAC, Kyoto, Japan, 3093–3095 (2010). [Google Scholar]], SOLEIL [9 C. Benabderrahmane, J. Phys., Conf. Ser., SRI 2012, Lyon, France 425, 032019-1-4 (2013). [Google Scholar]], and SPring-8 [10 T. Tanaka, Private communication (2015). [Google Scholar]].     

Germanium – the superior dopant in n‐type GaN

We present an experimental study about the influence of Si and Ge doping in GaN with focus on the occurring strain levels and overall crystalline quality. Extremely high quality samples were examined by means of Raman spectroscopy, demonstrating effective, n‐type doping concentrations up to the 5 × 10¹⁹ cm^–3 regime. By studying the full width at half maximum (FWHM) of the E₂(high) Raman mode with rising doping concentration, Ge is approved as the by far superior dopant if compared to Si. Even elevated nominal Ge concentrations yield corresponding FWHM values of just 3 cm^–1, a most competitive value even for bare bulk GaN samples. At the same time, the biaxial, compressive stress that is introduced by such high Ge doping amounts to just 0.2 GPa, in clear contrast to the particular case of silicon. Here, even moderate doping levels lead to tensile stress up to 1 GPa and consequently to a serious degeneration of the overall crystal quality as approved by our Raman analysis. Additionally, the examined high doping concentrations enable the observation of longitudinal optical phonon plasmon (LPP) modes in the Raman spectra, which serve as a direct tool for the determination of the effective doping concentration. A careful analysis of the LPP coupling at cryogenic and room temperature yields within the error interval identical free carrier concentrations in all germanium doped samples, pointing towards an energetically shallow nature of the dopant. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photoinduced rearrangements in transition metal compounds

In this contribution a range of photoinduced ligand rearrangements observed for the 1st and 2nd row transition metal and organometallic compounds are discussed. The processes discussed include photoinduced ligand exchange, linkage isomerisation and changes occurring within the coordination sphere of the compounds such as cis–trans and fac–mer isomerisations. The relevance of these processes for photocatalytic cycles or their application as synthetic tools is discussed where appropriate.