Thermal,Magnetic, Electronic,and Superconducting Properties of Rare‐Earth Metal Pentagermanides REGe5 (RE = La,Nd, Sm,Gd) and Synthesis of TbGe5

A series of isotypic rare‐earth metal pentagermanides including the new compound TbGe₅ were prepared by high‐pressure synthesis. They crystallize in the orthorhombic space group Immm [No. 71; a = 395.70(9) pm; b = 611.1(2) pm, and c = 983.6(3) pm for TbGe₅]. The crystal structure is isotypic to LaGe₅ and consists of puckered germanium slabs, which sandwich a second germanium species and the rare‐earth metal atoms. At ambient pressure, the thermal decomposition of the phases REGe₅ (RE = La, Nd, Sm, Gd, and Tb) proceeds via discrete intermediate steps into Ge(cF8) and thermodynamically stable germanium‐poorer phases. The investigated compounds REGe₅ are paramagnetic metallic conductors, which order antiferromagnetically at low temperatures. Specific heat measurements reveal that the superconducting state of LaGe₅ below T_c = 7.1(1) K is characterized by a critical field of μ₀H_c2 = 0.2 T and weak electron‐phonon coupling. Density‐functional based band‐structure calculations yield a very similar electronic structure for all the isotypic REGe₅ compounds. Besides a slight increase in the width of the valence band for smaller RE atoms, only minor differences are found for the two different germanium environments.     

Halogenomercury Salts of Sterically Crowded Triazenides – Convenient Starting Materials for Redox‐Transmetallation Reactions

Diaryl‐substituted triazenides Ar(Ar′)N₃HgX [Ar/Ar′ = Dmp/Mph, X = Cl ( 2a ), Br ( 3a ), I ( 4a ); Ar/Ar′ = Dmp/Tph, X = Cl ( 2b ), I ( 4b ) with Mph = 2‐MesC₆H₄, Mes = 2,4,6‐Me₃C₆H₂, Tph = 2′,4′,6′‐triisopropylbiphenyl‐2‐yl and Dmp = 2,6‐Mes₂C₆H₃] were synthesized by salt‐metathesis reactions in ethyl ether from the readily available starting materials Ar(Ar′)N₃Li and HgX₂. These compounds may be used for redox‐transmetallation reactions with rare‐earth or alkaline earth metals. Thus, reaction of 4b or 2b with magnesium or ytterbium in tetrahydrofuran afforded the triazenides Dmp(Tph)N₃MX(thf) ( 5b : M = Mg, X = I; 6b : M = Yb, X = Cl) in good yield. All new compounds were characterized by melting point, ¹H and ¹³C NMR spectroscopy and for selected species by IR spectroscopy or mass spectrometry. In addition, the solid‐state structures of triazenides 2a , 2b , 3a , 4b , 5b and 6b were investigated by single‐crystal X‐ray diffraction.     

Reaktionen des metalloiden Clusteranions {Ge9[Si(SiMe3)3]3}– in der Gasphase. Oxidations‐ und Reduktionsschritte geben Einblicke in den Bereich zwischen metalloiden Clustern und Zintl‐Ionen

The cluster anion {Ge₉[Si(SiMe₃)₃]₃}^– ( 1 ) is transferred intact into the gas phase via the electro spray method. Subsequently the fragmentation of 1 after resonant excitation as well as the oxidation reaction with O₂ and Cl₂ are investigated in an FT‐ICR mass spectrometer (Fourier Transform Ion Cyclotron Resonance). Unlike former results with off‐resonant excitation the fragmentation leads mainly to the end‐product Ge₉^–. Moreover, applying an on‐resonant excitation the dissociation experiment can be quantified; 2.0 ± 0.15 eV (193 ± 15kJ · mol^–1) for the elimination of the first two ligands and 2.7 ± 0.15 eV (261 ± 15 kJ · mol^–1) for all ligands, respectively. Particular attention is turned on the first step, where sterically encumbered Si₂(SiMe₃)₆ molecules are formed in a concerted reaction. This result, which is also important for elemental reactions on metal surfaces in catalyses, is based on experimentally determined threshold energies, DFT calculations and calculations on the lifetime of the involved species., In contrast to the high reactivity of crystalline 1 ·Li(THF)₄, gaseous 1 is inert against oxygen. The analogy to recently published spin forbidden reactions of Al₁₃^– with O₂ hints to a general importance of spin conversion during gas phase reactions of larger cluster molecules. The oxidation of 1 with Cl₂ proceeds through different reaction channels. DFT calculations give a first insight on the complex primary oxidation steps. These calculations also reveal that the delocalized bonding situation in the Ge₉ core is distorted upon oxidation. This result together with the dissociation experiments shed more light on differences and similarities between metalloid clusters and Zintl ions.     

Light-controlled directional liquid drop movement on TiO2 nanorods-based nanocomposite photopatterns

Patterned polymeric coatings enriched with colloidal TiO(2) nanorods and prepared by photopolymerization are found to exhibit a remarkable increase in their water wettability when irradiated with UV laser light. The effect can be completely reversed using successive storage in vacuum and dark ambient environment. By exploiting the enhancement of the nanocomposites hydrophilicity upon UV irradiation, we prepare wettability gradients along the surfaces by irradiating adjacent surface areas with increasing time. The gradients are carefully designed to achieve directional movement of water drops along them, taking into account the hysteresis effect that opposes the movement as well as the change in the shape of the drop during its motion. The accomplishment of surface paths for liquid flow, along which the hydrophilicity gradually increases, opens the way to a vast number of potential applications in microfluidics.     

Synthesis, properties and perspectives of hybrid nanocrystal structures

Current efforts and success of nanoscale science and technology are related to the fabrication of functional materials and devices in which the individual units and their spatial arrangement are engineered down to the nanometer level. One promising way of achieving this goal is by assembling colloidal inorganic nanocrystals as the novel building blocks of matter. This trend has been stimulated by significant advances in the wet-chemical syntheses of robust and easily processable nanocrystals in a wide range of sizes and shapes. The increase in the degree of structural complexity of solution-grown nanostructures appears to be one of the natural directions towards which nanoscience will increasingly orient. Recently, several groups have indeed devised innovative syntheses of nanocrystals through which they have been able to group inorganic materials with different properties in the same particle. These approaches are paving the way to the development of nanosized objects able to perform multiple technological tasks. In this critical review (165 references), we will summarize the recent advances in the synthesis of colloidal nanocrystals, with emphasis on the strategies followed for the fabrication of nano-heterostructures, as well as on their properties and the perspectives in this field.     

Hydrothermal Synthesis and Crystal Structure of Novel Alkali Trimolybdates

Novel alkali trimolybdates of the triclinic (M, M′)₂Mo₃O₁₀ (M = Rb; M′ = K, Cs) type were obtained through a systematic hydrothermal approach based on the reaction of MoO₃ with alkali halide solutions at 180 °C. The crystal structures were determined from X‐ray single crystal data. The alkali trimolybdates extend the family of known alkali trimolybdates in an unexpected fashion, because they contain a distorted variation of [Mo₃O₁₀]^2? chains as a key structural motif that has only been found in a single compound before, namely ethylenediammonium trimolybdate, (C₂H₁₀N₂)[Mo₃O₁₀]. The applied hydrothermal strategy is discussed in the general context of systematic pathways to polyoxomolybdates. Furthermore, the templating role of the alkali cations and their interaction with the polyoxomolybdate surroundings is compared to (C₂H₁₀N₂)[Mo₃O₁₀] in terms of electrostatic calculations.     

Low-temperature synthesis of soluble and processable organic-capped anatase TiO2 nanorods

We demonstrate the controlled growth of high aspect ratio anatase TiO2 nanorods by hydrolysis of titanium tetraisopropoxide (TTIP) in oleic acid (OLEA) as surfactant at a temperature as low as 80 degrees C. Chemical modification of TTIP by OLEA is proven to be a rational strategy to tune the reactivity of the precursor toward water. The most influential factors in shape control of the nanoparticles are investigated by simply manipulating their growth kinetics. The presence of tertiary amines or quaternary ammonium hydroxides as catalysts is essential to promote fast crystallization under mild conditions. The novelty of the present approach relies on the large-scale production of organic-capped TiO2 nanocrystals to which standard processing of colloidal nanocrystals, such as surface ligand exchange, can be applied for the first time. Concentrated colloidal titania dispersions can be prepared for a number of fundamental studies in homogeneous solutions and represent a new source of easily processable oxide material for many technological applications.     

Structural Investigations and Thermal Behaviour of Mercury(II) Sulfito Complexes

The crystal structures of (NH₄)[HgSO₃Cl] ( 1 ) and of (NH₄)₂[Hg(SO₃)₂] ( 2 ) were determined from single crystal diffractometer data sets. 1 : 22 °C, Pnma, Z = 4, a = 15.430(3), b = 5.525(1), c = 6.679(1) Å, R(F) = 0.0256, R_w(F²) = 0.0642 (all 1056 unique reflections). 2 : ?108 °C, P2₁2₁2₁, Z = 4, a = 6.2240(4), b = 9.3908(6), c = 13.6110(8) Å, R(F) = 0.0179, R_w(F²) = 0.0493 (all 2699 unique reflections). The structure of 1 contains bent Cl‐Hg‐SO₃ entities (site symmetry m; d(Hg‐Cl) = 2.3403(13) Å, d(Hg‐S) = 2.3636(12) Å, ∠(Cl‐Hg‐S) = 164.51(5)°, d(S‐O) 2×1.458(3) Å, 1.468(4) Å, = 1.461Å) linked to undulated ribbons parallel to the b ‐axis by intermolecular secondary bonds SO···Hg (d(O···Hg) = 2×2.595(3) Å). These ribbons in turn aggregate to layers around the bc ‐plane. The layers are stacked along the a ‐axis with interlayer distances of a /2. The structure of 2 is made up of O₃S‐Hg‐SO₃ moieties (d(Hg‐S) = 2.3935(7), 2.3935(8) Å; ∠(Hg‐S‐Hg) = 174.41(3)°; = 1.474Å), that are linked to ribbons parallel to the a axis by coordination of Hg to three remote O atoms (2.801(4) < d(Hg‐O) < 2.844(3) Å). Adjacent ribbons are joined together by an additional Hg‐O contact of 2.733(3) Å, leading to a three‐dimensional anionic framework. Both crystal structures are stabilised by disordered NH₄⁺ cations, placed between the anionic layers or in the vacancies of the framework, via moderate hydrogen bonding interactions N‐H···O with donor‐acceptor distances ranging from 2.8 to 3.2Å. 1 and 2 were further characterised by thermal analysis (TG, DSC). They start to decompose at temperatures above 130 °C.     

Control of the water adhesion on hydrophobic micropillars by spray coating technique

We present an alternative approach for controlling the water adhesion on solid superhydrophobic surfaces by varying their coverage with a spray coating technique. In particular, micro-, submicro-, and nanorough surfaces were developed starting from photolithographically tailored SU-8 micropillars that were used as substrates for spraying first poly(tetrafluoroethylene) submicrometer particles and subsequently iron oxide nanoparticles. The sprayed particles serve to induce surface submicrometer and nanoscale roughness, rendering the SU-8 patterns superhydrophobic (apparent contact angle values of more than 150°), and also to tune the water adhesion between extreme states, turning the surfaces from “non-sticky” to “sticky” while preserving their superhydrophobicity. The influence of the chemical properties and of the geometrical characteristics of the functionalized surfaces on the wetting properties is discussed within the frame of the theory. This simple method can find various applications in the fabrication of microfluidic devices, smart surfaces, and biotechnological and antifouling materials.