Magnetization relaxation in the single-ion magnet DySc2N@C80: quantum tunneling, magnetic dilution, and unconventional temperature dependence.

Relaxation of magnetization in endohedral metallofullerenes DySc2N@C80 is studied at different temperatures, in different magnetic fields, and in different molecular arrangements. Magnetization behavior and relaxation are analyzed for powder sample, and for DySc2N@C80 diluted in non-magnetic fullerene Lu3N@C80, adsorbed in voids of a metal-organic framework, and dispersed in a polymer. The magnetic field dependence and zero-field relaxation are also studied for single-crystals of DySc2N@C80 co-crystallized with Ni(ii) octaethylporphyrin, as well as for the single crystal diluted with Lu3N@C80. Landau-Zener theory is applied to analyze quantum tunneling of magnetization in the crystals. The field dependence of relaxation rates revealed a dramatic dependence of the zero-field tunneling resonance width on the dilution and is explained with the help of an analysis of dipolar field distributions. AC magnetometry is used then to get access to the relaxation of magnetization in a broader temperature range, from 2 to 87 K. Finally, a theoretical framework describing the spin dynamics with dissipation is proposed to study magnetization relaxation phenomena in single molecule magnets.

Flexible metal-organic frameworks.

Advances in flexible and functional metal-organic frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009-2013 with reference to the early pertinent work since the late 1990s. Flexible MOFs combine the crystalline order of the underlying coordination network with cooperative structural transformability. These materials can respond to physical and chemical stimuli of various kinds in a tunable fashion by molecular design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host-guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallographic phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theoretical approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chemistry with the linker molecules controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-solution concept are included, and as well examples of possible applications of flexible metal-organic frameworks for separation, catalysis, sensing, and biomedicine.

Highly transparent Bi2MoO6- and Bi2WO6-polymer nanocomposites.

A combined method of precipitation, phase transfer into organic solvent, solvothermal treatment and subsequent in situ polymerization was used to integrate nanocrystalline Bi2MoO6- and Bi2WO6-particles into a polymer matrix of poly-laurylacrylate. The presented method offers a new and gentle way to produce highly transparent bulk nanocomposites containing evenly distributed Bi2MoO6- and Bi2WO6-nanoparticles. Characterization results of DLS-, XRD-, REM- and TEM-measurements are presented as well as solid state UV/VIS-measurements of the particles. The transparent nanocomposites were characterized using UV/VIS-spectroscopy and ellipsometry. All composites show a good transmission in the range from 800-400 nm. The particle content of the nanocomposites was measured with TG-measurements.

Adaptive response of a metal-organic framework through reversible disorder-disorder transitions.

The ultrahigh porosity and varied functionalities of porous metal-organic frameworks make them excellent candidates for applications that range widely from gas storage and separation to catalysis and sensing. An interesting feature of some frameworks is the ability to open their pores to a specific guest, enabling highly selective separation. A prerequisite for this is bistability of the host structure, which enables the framework to breathe, that is, to switch between two stability minima in response to its environment. Here we describe a porous framework DUT-8(Ni)-which consists of nickel paddle wheel clusters and carboxylate linkers-that adopts a configurationally degenerate family of disordered states in the presence of specific guests. This disorder originates from the nonlinear linkers arranging the clusters in closed loops of different local symmetries that in turn propagate as complex tilings. Solvent exchange stimulates the formation of distinct disordered frameworks, as demonstrated by high-resolution transmission electron microscopy and diffraction techniques. Guest exchange was shown to stimulate repeatable switching transitions between distinct disorder states.

Structure and mechanical properties of transparent ZnO/PBDMA nanocomposites.

The structural, optical and mechanical characterization of ZnO/PBDMA (poly(butanediolmonoacrylate)) nanocomposites is presented. ZnO nanoparticles are homogenously dispersed in the polymer matrix in transmission electron microscopy (TEM) images of ultramicrotomed sections. The size of the ZnO nanoparticles can be controlled during synthesis in a range of 6-10 nm as determined by dynamic light scattering (DLS). TEM and small-angle X-ray scattering (SAXS) investigations show a homogeneous dispersion for the 6 nm sized particles in the resulting nanocomposites. Due to the low scattering of small, well dispersed particles, the transparency for visible light of the nanocomposites is very high (transmittance > 91% for lambda = 600 nm), while the haze is below 1%. ZnO nanoparticles act as a strong UV-absorber, causing a transmittance below 0.05% for wavelengths smaller than 350 nm in the nanocomposites. For the composite containing 6 nm sized particles, a green luminescence band, centered at 538 nm, is observed using fluorescence spectroscopy, while the excitation of the fluorescence has a maximum at 357 nm. Both, excitation and emission maxima, depend on the size of the particles and are shifted to higher wavelength when larger particles were used. Furthermore, the nanoparticles strongly influence the mechanical properties and the glass transition temperature of the nanocomposites. The addition of 4.5 wt% ZnO to PBDMA leads to an increase in modulus from 70.8 MPa to 139.1 MPa (increase 10 nearly 200%) and in tensile strength from 5.2 MPa to 9.5 MPa (increase to 180%) retaining the elongation at break nearly unchanged (decrease from 13.4% to 10.1%). The sample is much stiffer and exhibits a higher work of fracture due to the nanofiller addition. As compared to the unmodified materials, the glass transition temperature is enhanced by 5 K in the case of the nanocomposite sample.

Surface functionalization of ZrO2 nanocrystallites for the integration into acrylate nanocomposite films.

Surface functionalized zirconia nanoparticles were prepared by covalent grafting of a methacrylate functionalized silane (methacryloxypropyltrimethoxysilane, MPTS) onto the surface of the zirconia nanoparticles (tetragonal and mixed monoclinic/tetragonal phase) obtained by hydrothermal treatment of zirconyl chloride octahydrate. The particles are 70 nm aggregates of nanometric primary grains (4-12 nm) with inter particle porosity. BET measurements show that the specific surface area of the particles after activation at 100 degrees C is between 85 and 204 m2/g depending on the mineralizer used (Sr2+, Ca2+, Mg2+). IR-measurements show that the surface of the particles can be covered with functional groups bound through a variable number of ZrOSi bonds to render them organocompatible. The surface modified particles were dispersed in monomer solution (butanediol monoacrylate, BDMA) and polymerized to form films by adding a cross linking agent (trimethylolpropane triacrylate, Laromer TMPTA) and an UV initiator (2,4,6-trimethylbenzoyldiphenylphosphine oxide, Lucirin TPO). The received films were characterized with thermogravimetry and UV-vis spectroscopy.

Bioinspired carbide-derived carbons with hierarchical pore structure for the adsorptive removal of mercury from aqueous solution.

Biosilica of the diatom species Thalassiosira pseudonana is used as hard template for the synthesis of silicon carbide-derived carbons. The typical species-specific macroporous structure is retained during the nanocasting-chlorine treatment process and the resulting materials exhibit very high specific surface areas up to 2300 m2 g-1. Bioinspired carbons show very high capacities in mercury adsorption from aqueous solution compared to reference materials.

CFA-4 - a fluorinated metal-organic framework with exchangeable interchannel cations.

The syntheses and crystal structures of the fluorinated linker 1,4-bis(3,5-bis(trifluoromethyl)-1H-pyrazole-4-yl)benzene (H2-tfpb; 1) and the novel metal-organic framework family M[CFA-4] (Coordination Framework Augsburg University-4), M[Cu5(tfpb)3] (M = Cu(i), K, Cs, Ca(0.5)), are described. The ligand 1 is fully characterized by single crystal X-ray diffraction, photoluminescence-, NMR-, IR spectroscopy, and mass spectrometry. The copper(i)-containing MOF crystallizes in the hexagonal crystal system within the chiral space group P6322 (no. 182) and the unit cell parameters are as follows: a = 23.630(5) Å, c = 41.390(5) Å, V = 20 015(6) Å3. M[CFA-4] features a porous 3-D structure constructed from pentanuclear copper(i) secondary building units {Cu(pz)6}- (pz = pyrazolate). Cu(I)[CFA-4] is fully characterized by synchrotron single crystal X-ray diffraction, thermogravimetric analysis, variable temperature powder X-ray diffraction, IR spectroscopy, photoluminescence and gas sorption measurements. Moreover, thermal stability and gas sorption properties of K[CFA-4] and Cu(I)[CFA-4] are compared.

Influence of precursor porosity on sodium and sulfur promoted iron/carbon Fischer-Tropsch catalysts derived from metal-organic frameworks.

Iron-based metal-organic frameworks (MOFs) with varying porosity are converted by pyrolysis into iron/carbon catalysts with predetermined composition and tailored pore structural features for the Fischer-Tropsch synthesis of lower C2-C4 olefins. Significantly higher activity arises for catalysts with higher porosity and decreased iron particle size derived from hierarchical MOF xerogel/aerogel precursors as compared to a purely microporous MOF. Post-synthetic functionalization using sodium and sulfur promoters further enhances the catalytic properties.

Integration of zinc oxide nanoparticles into transparent poly(butanediolmonoacrylate) via photopolymerisation.

A new method for the preparation of transparent ZnO/PBDMA nanocomposites (PBDMA = poly(butanediolmonoacrylate)) is reported. Zinc oxide nanocrystals (4-10 nm) were synthesized in ethanol and then transferred into butanediolmonoacrylate (BDMA) to obtain a transparent and stable colloidal suspension. No further growth or aggregation of the particles could be observed, after dispersing the particles in the monomer. Effective size control in the range of 6-10 nm and concentrations up to 10 wt% zinc oxide were demonstrated for these systems. The particles and suspensions were characterized by transmission electron microscopy, X-ray diffraction, UV-VIS spectroscopy and dynamic light scattering. The addition of trimethylolpropane triacrylate (TMPTA) and a photoinitiator to the ZnO/BDMA suspension lead to a UV-curable liquid. Photoinduced polymerization was used to produce transparent nanocomposites containing the nanoparticles. The material exhibits a strong UV absorption below 360 nm, a high transmission (90%) in the visible spectral range and a green photoluminescence.

Microemulsion flame pyrolysis for hopcalite nanoparticle synthesis: a new concept for catalyst preparation.

A new route to highly active hopcalite catalysts via flame spray pyrolysis of an inverse microemulsion precursor is reported. The nitrate derived nanoparticles are around 15 nm in diameter and show excellent conversion of CO under ambient conditions, outperforming commercial reference hopcalite materials produced by co-precipitation.

[Erbium:YAG laser vitrectomy. Initial clinical results]. / Erbium: YAG-Laser-Vitrektomie. Erste klinische Ergebnisse.

BACKGROUND: Much interest has been expressed in recent years in the use of erbium:YAG lasers in ophthalmology, particularly for vitrectomy and phacoemulsification. PATIENTS AND METHODS: We performed 54 operations (49 primary, 5 secondary) for pars plana vitrectomy on 53 eyes of 53 patients using the Phacolase erbium:YAG laser at a frequency of 10-100 Hz single-pulse energy of 5-50 mJ. RESULTS: The operation was successful in 51 cases,while in three we had to resort to mechanical vitrectomy due to initial technical problems. CONCLUSION: Erbium:YAG laser vitrectomy was generally fast and caused little mechanical stress to the retina. Complications were only those known from mechanical vitrectomy.The handpiece showed good properties for removing vitreous but not for cutting membranes, although new handpieces specifically for the cutting of membranes are under development.

[Phacoemulsification and vitrectomy with the erbium:YAG laser and phacoemulsification with the neodymium:YAG laser]. / Phakoemulsifikation und Vitrektomie mit dem Erbium:YAG-Laser sowie Phakoemulsifikation mit dem Neodymium:YAG-Laser.

There are an increasing number of possible applications for the use of Erbium:YAG and Neodymium:YAG lasers in ophthalmology. Laser-phacoemulsification as well as Erbium-laser vitrectomy is of major interest. We report on the underlying technology and more than 1-year-experience using the PHACOLASE (Asclepion-Meditec, Jena, Germany, 10-100 Hz frequency, 5-50 mJ single pulse energy) for phacoemulsification and pars plana vitrectomy and the Lyla-Dodick laser photolysis (A.R.C. Laser, Eckental-Forth, Germany, 1-20 Hz, up to 8 mJ single pulse energy). The Erbium:YAG-laser as well as the Neodymium:YAG-laser enabled us to extract lenses with up to medium hard nuclei. Moreover, the Erbium laser enabled fast vitrectomy with little mechanical traction. In many of our initial surgical operations we had to change to mechanical vitrectomy due to initial technical problems. No new complications occurred intra- or postoperatively. The handpiece worked well in removing vitreous bodies, but was not feasible for cutting membranes. Modified handpieces for this purpose are under development.

Shuttle suppression in room temperature sodium-sulfur batteries using ion selective polymer membranes.

A sodiated Nafion-coating on a porous polypropylene backbone was used as a cation selective separator for room temperature sodium-sulfur batteries. The capacity of the cells after 20 cycles could be enhanced by 75% to 350 mA h g(sulfur)(-1) using the new separator.

Functional inorganic nanofillers for transparent polymers.

The integration of inorganic nanoparticles into polymers has been used for the functionalization of polymer materials with great success. Whereas in traditional polymer composites, micron sized particles or agglomerates typically cause significant light scattering hampering optical applications, in nanocomposites the particle dimensions are small enough for the production of highly transparent composites. A challenge for the generation of such materials is to develop an integrated synthesis strategy adapting particle generation, surface modification and integration inside the polymer. Surface grafting using polymerizable surfactants or capping agents allows for linking the particles to the polymer. Novel techniques such as in situ polymerization and in situ particle processing are beneficial to avoid aggregation of inorganic particles inside the polymer matrix. The functions associated with inorganic fillers are widespread. Layered silicates and related materials are nowadays commercially available for improving mechanical and barrier properties in packaging. With the availability of highly transparent materials, the focus has shifted towards optical functions such as luminescence and UV-protection in transparent polymers. IR-active fillers are used in laser-holography for transparent poly(methyl methacrylate) (PMMA) nanocomposites. Refractive index modulation and ultrahigh refractive index films were developed based on inorganic materials such as PbS. The integration of magnetic nanoparticles has a great potential for applications such as electromagnetic interference shielding and magneto-optical storage. This tutorial review will summarize functions associated with the integration of inorganic nanofillers in polymers with a focus on optical properties.

Polymerization of w/o microemulsions for the preparation of transparent SiO2/PMMA nanocomposites.

Reverse w/o microemulsions composed of methyl methacrylate (MMA) forming the oil phase, nonionic surfactants, and water are used for the synthesis of transparent SiO2/PMMA nanocomposites. An inorganic precursor, tetraethoxysilane (Si(OEt)(4), TEOS), is hydrolyzed in the reverse micelles containing aqueous ammonia. During the hydrolysis of TEOS, polymerization of the continuous MMA phase is initiated using AIBN (azobisisobutyronitrile), and after thermal polymerization at 333 K for 12 h, solid blocks of PMMA are obtained in which nanometer-sized silica particles are trapped in the solid polymer matrix. According to small-angle X-ray and dynamic light scattering experiments, the water droplets in MMA microemulsions are 12 nm (R(W) = 13) in diameter, whereas after polymerization of the microemulsion, the SiO2 particles in the transparent SiO2/PMMA composites are 26 nm in diameter. Transmission electron micrographs demonstrate a low degree of agglomeration in the composites. In comparison with materials generated from micelle-free solutions, the particle size distribution is narrow. The reverse micelle-mediated approach produces composites of high transparency comparable with that of pure PMMA.

Synthesis, structure, and bonding of A5Cd2Tl11, A = Cs, Rb. Naked pentagonal antiprismatic columns centered by cadmium.

A new anionic thallium cluster chain 1 infinity[Cd2Tl11(5-)] has been discovered in the A-Cd-Tl systems for A = Cs, Rb. The compounds are synthesized by direct fusion of the elements at 700 degrees C and equilibration of the quenched product at 200 degrees C for 1 month. The thallides crystallize in the orthorhombic space group Amm2, Z = 2, a = 56107(7) and 55999(6) A, b = 18090(3) and 17603(3) A, c = 13203(3) and 12896(2) A for A = Cs and Rb, respectively, and contain chains of face-sharing pentagonal Tl10 antiprisms embedded in a matrix of alkali metal cations. Cadmium atoms occupy the center of the antiprisms and donate electrons to the anionic chain. Additional four-bonded Tl atoms on one side of the chain make the structure acentric. The compounds are diamagnetic (chi 296 = -08, -40 (x 10(-4) emu/mol, respectively) and metallic (10-20 mu omega cm at 275 K), and the indirect band gap energy of both compounds is close to zero according to extended Hückel calculations on the isolated chain.

Synthesis and structure of K10Tl7: the first binary trielide containing naked pentagonal bipyramidal Tl7 clusters.

The title compound is synthesized by direct fusion of the elements at 400 degrees C followed by annealing at 330 degrees C, quenching to room temperature, and subsequent annealing at 120 and 100 degrees C for days to weeks. The compound crystallizes in the monoclinic space group P21/c (No. 14), with Z = 4, a = 10.132(1) A, b = 22.323(2) A, c = 13.376(1) A, and beta = 93.14(1)degrees, and consists of Tl7(7-) clusters embedded in a matrix of potassium ions. The cluster is an axially compressed pentagonal bipyramid close to D5h symmetry. The apex-apex bond distance (3.462(1) A) is little longer than the bonds in the pentagonal waist (3.183(1)-3.247(1) A). Structurally the compound is not electron-precise: K10Tl7 has three extra electrons per Tl7 cluster and is Pauli paramagnetic (chi300 = 2.25 x 10(-4) emu/mol).