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.     

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.     

Compressible or incompressible blend of interacting monodisperse linear polymers near a surface

We consider a lattice model of a mixture of repulsive, attractive, or neutral monodisperse linear polymers of two species, A and B, with a third monomeric species C, which may be taken to represent free volume. The mixture is confined between two hard, parallel plates of variable separation whose interactions with A and C may be attractive, repulsive, or neutral, and may be different from each other. The interactions with A and C are all that are required to completely specify the effect of each surface on all three components. We numerically study various density profiles as we move away from the surface, by using the recursive method of Gujrati and Chhajer [J. Chem. Phys. 106, 5599 (1997)] that has already been previously applied to study polydisperse solutions and blends next to surfaces. The resulting density profiles show the oscillations that are seen in Monte Carlo simulations and the enrichment of the smaller species at a neutral surface. The method is computationally ultrafast and can be carried out on a personal computer (PC), even in the incompressible case, when Monte Carlo simulations are not feasible. The calculations of density profiles usually take less than 20 min on a PC.     

Molecular and Spectroscopic Characterization of Green and Red Cyanine Fluorophores from the Alexa Fluor and AF Series**

The use of fluorescence techniques has an enormous impact on various research fields including imaging, biochemical assays, DNA-sequencing and medical technologies. This has been facilitated by the development of numerous commercial dyes with optimized photophysical and chemical properties. Often, however, information about the chemical structures of dyes and the attached linkers used for bioconjugation remain a well-kept secret. This can lead to problems for research applications where knowledge of the dye structure is necessary to predict or understand (unwanted) dye-target interactions, or to establish structural models of the dye-target complex. Using a combination of optical spectroscopy, mass spectrometry, NMR spectroscopy and molecular dynamics simulations, we here investigate the molecular structures and spectroscopic properties of dyes from the Alexa Fluor (Alexa Fluor 555 and 647) and AF series (AF555, AF647, AFD647). Based on available data and published structures of the AF and Cy dyes, we propose a structure for Alexa Fluor 555 and refine that of AF555. We also resolve conflicting reports on the linker composition of Alexa Fluor 647 maleimide. We also conducted a comprehensive comparison between Alexa Fluor and AF dyes by continuous-wave absorption and emission spectroscopy, quantum yield determination, fluorescence lifetime and anisotropy spectroscopy of free and protein-attached dyes. All these data support the idea that Alexa Fluor and AF dyes have a cyanine core and are a derivative of Cy3 and Cy5. In addition, we compared Alexa Fluor 555 and Alexa Fluor 647 to their structural homologs AF555 and AF(D)647 in single-molecule FRET applications. Both pairs showed excellent performance in solution-based smFRET experiments using alternating laser excitation. Minor differences in apparent dye-protein interactions were investigated by molecular dynamics simulations. Our findings clearly demonstrate that the AF-fluorophores are an attractive alternative to Alexa- and Cy-dyes in smFRET studies or other fluorescence applications.     

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.     

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.     

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.     

Thermodynamic Comparison and the Ideal Glass Transition of Antiferromagnetic Ising Model on Multi-branched Husimi and Cubic Recursive Lattice with the Identical Coordination Number

Two types of recursive lattices with the identical coordination number but different unit cells (2-D square and 3-D cube) are constructed and the antiferromagnetic Ising model is solved exactly on them to study the stable and metastable states. A multi-branched structure of the 2-D plaquette model, which we introduced in this work, makes it possible to be an analog to the cubic lattice. Two solutions of each model can be found to exhibit the crystallization of liquid, and the ideal glass transition of supercooled liquid respectively. Based on the solutions, the thermodynamics on both lattices, e.g. the free energy, energy density, and entropy of the supercooled liquid, crystal, and liquid state of the model are calculated and compared with each other. Interactions between particles farther away than the nearest neighbor distance and multi-spins interactions are taken into consideration, and their effects on the thermal behavior are examined. The two lattices show comparable properties on the thermodynamics, which proves that both of them are practical to describe the regular 3-D case, especially to locate the ideal glass transition, while the 2-D multi-branched plaquette model is less accurate with the advantage of simpler formulation and less computation time consumption.