Solvent free reactions in the solid state: solid state metathesis

Transition Metal Chemistry -     

Nanotechnology – a challenge for solid state analysis

The characterisation of nanoscaled structures is an essential part of nanotechnology. Using nanoscaled Co/Cu multilayers as an example of magnetoelectronic devices, the dependence of the layer formation mechanism on the deposition method (pulsed laser deposition and sputtering) is shown. The evolution of the thermal deterioration of Co (2 nm)/Cu (2 nm) multilayers during annealing can be understood using a combination of Monte-Carlo simulations and observations of intermediate steady states. It is shown that analytical TEM, especially energy-filtered imaging, is excellently qualified for this kind of characterisation.     

A Dodecagonal Quasicrystalline Chalcogenide

Diffractograms with twelvefold rotational symmetry (depicted on the right) were obtained from the first quasicrystalline chalcogenide Ta_1.6Te. This compound was prepared on a preparative scale by the reduction of TaTe₂ with tantalum below 1870 K. This tantalum-rich telluride, which is the first stable dodecagonal phase, has enabled an in-depth investigation of this unusual state of ordering.     

Retarded solid state reactions

Reconstructive phase transitions and formation or decomposition reactions in the solid state exhibit in DTA-measurements a more or less great hysteresis between the temperatures from heating and cooling curves; at worst the reaction can be suppressed completely. By e.m.f.vs. T-measurements in appropriate galvanic cells for solid electrolytes equilibrium temperatures in the case of such kinetic hindrance can be determined and additionally the existence of metastable states can be proved.

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Zusammenfassung Rekonstruktive Phasenumwandlungen sowie Bildungs- und Zersetzungsreaktionen im festen Zustand zeigen bei DTA-Messungen eine mehr oder minder große Hysteresis zwischen den aus Aufheiz- bzw. Abkühlkurven ermittelten Temperaturen; schlimmstenfalls kann die Festkörperreaktion völlig unterdrückt sein. Mißt man in geeigneten galvanischen Zellen für Festelektrolyte EMK-gegen-T-Kurven, so erhält man auch im Falle kinetischer Hemmungen Gleichgewichtstemperaturen und kann darüber hinaus das Vorliegen metastabiler Zustände nachweisen.

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We have to thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industry for supporting our work from the outset.     

Selective solid state photooxidant

Irradiation of biphenyl encapsulated in the cavities of a NaZSM-5 zeolite framework has been reported to result in the formation of an extremely long-lived radical cation. Here, we show that such zeolite encapsulated radical cations can act as irreversible one-electron oxidants for simple alkenes and dienes, in a solid-state analogue to solution-phase cosensitization. Compared to the well-known semiconductor photooxidizers, such as titanium dioxide, the NaZSM-5 zeolite-based solid photooxidants exhibit enhanced selectivity based on oxidation potential, molecular size and shape, and Lewis base character.     

Stereoselectivity reversal of a photochemical reaction in the solid state

The stereoselectivity of Norrish type II cyclobutanol formation resulting from photolysis of α-adamantyl-p-methoxyacetophenone is altered in favor of the more hindered cis isomer as the reaction medium is changed from isotropic liquid phases (benzene or acetonitrile) to the pure crystal. Based on the reactant X-ray crystal structure, it is suggested that the intermediate 1,4-biradical in the solid state is born in, and restricted to, a conformation which is ideal for direct closure to the more hindered product. In the relatively unrestricted solution environment, however, conformational isomerism of the biradical is faster than closure, thus leading to a predominance of the less hindered trans cyclobutanol.     

Ferroelectricity in solid state chemistry

This article discusses some state-of-the-art aspects of solid state chemistry within the context of ferroelectric materials such as oxides, fluorides and oxyfluorides, whose crystalline networks include octahedra. Structural considerations make it possible to determine the origin of the ferroelectricity and to predict the existence of polar properties in new families. Crystallographic distortions of different nature lead to highly variable transition sequences. Ferroelectricity is often associated with ferroelasticity. The Curie temperature is linked to the composition and to the chemical bond. In this respect, several factors are to be considered, e.g. size, coordination and configuration of the cations, covalence of bonds, order-disorder, etc. Physical studies are very useful: first, the dielectric characteristics and their variations with temperature, frequency and electric field are typical of ferroelectrics; second, the pyroelectric, piezoelectric, electro-optical and non-linear optical properties are among the most effective. Various types of materials (single crystals, ceramics, thin films) are used nowadays in a wide range of applications. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASferroelectricity / solid state chemistry     

Atomic solid state energy scale

A plot of electron affinity (EA) and ionization potential (IP) versus energy band gap (E(G)) for 69 binary closed-shell inorganic semiconductors and insulators reveals that E(G) is centered about the hydrogen donor/acceptor ionization energy ε(+/-). Thus, ε(+/-), or equivalently the standard hydrogen electrode (SHE) energy, functions as an absolute energy reference, determining the tendency of an atom to be either a cation or anion in a compound. This empirical trend establishes the basis for defining a new solid state energy (SSE) scale. This SSE scale makes possible simple approaches for quantitatively assessing electronegativity, chemical hardness, and ionicity, while also providing new insight into the periodic trends of solids.     

Isoconversional analysis of solid state transformations

There are many mathematical methods to determine the activation energy from non-isothermal experiments. However, controversies arise over the different values obtained by these methods. We will show that the origin of these discrepancies is either inaccurate approximations of the so-called temperature integral or the occurrence of complex transformations. We will review and compare the most commonly used methods. For those methods that lack accuracy, we will introduce simple numerical modifications to make them exact. In addition, we will introduce a new method that allows easy and accurate determination of the activation energy.     

Isoconversional analysis of solid state transformations

We will analyze the discrepancies between isoconversional methods when applied to complex transformations. The practical analysis of particular transformations leads us to conclude that (a) conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy; and (b) experimental inaccuracies and noise tend to give an apparent evolution of the energy variation, so that, non-constancy of the activation energy does not necessarily mean deviations from single-step transformations with constant activation energy.     

Heat capacity of solid state proteins

In an ongoing effort to understand the thermodynamic properties of proteins, ovalbumin, lactoglobulin, lysozyme are studied by adiabatic and differential scanning calorimetry over wide temperature ranges. The heat capacities of the samples in their pure, solid states are linked to an approximate vibrational spectrum with the ATHAS analysis that makes use of known group vibrations and a set of parameters, Θ₁ and Θ₃, of the Tarasov function for the skeletal vibrations. Good agreement is found between experiment and calculation with rms errors mostly within ±3%. The analyses were also carried out with an empirical addition scheme using data from polypeptides of naturally occurring amino acids. Due to space limitation, only selected results are reported.     

Fifty years of solid state chemistry

This review article dedicated to Jean Rouxel (1935–1998), whose research on low-dimensional materials strongly influenced modern solid state chemistry, retraces some of the major steps of its pluridisciplinary development. Significant achievements are mentioned in the scope of their scientific context but often also for facing industrial requirements.     

The complex synthesis and solid state chemistry of ceria-lanthana solid solutions prepared via a hexamethylenetetramine precipitation

Mixed oxide solid solutions are becoming ever more commercially important across a range of applications. However, their synthesis can be problematical. Here, we show that ceria-lanthana solid solutions can be readily prepared via simple precipitation using hexamethylenetetramine. However, the solution chemistry can be complex, which results in the precipitated particles having a complex structure and morphology. Great care must be taken in both the synthesis and characterisation to quantify the complexity of the product. Even very high heat treatments were not able to produce highly homogeneous materials and X-ray diffractions reveals the non-equilibrium form of particles prepared in this way. Unexpected crystal structures are revealed including a new metastable cubic La₂O₃ phase.     

Supramolecular organization in the solid state of a novel soluble polydiacetylene

The synthesis of the monomer 1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne, its polymerization and the purification of the polymer, which is soluble in common organic solvents, are reported. Results from powder X-ray diffraction studies carried out on the red form of the polymer are discussed. The red polymer chains self-assemble into cylindrical shapes which produce hexagonal columnar mesophases with a transition from a more (Colho) to a less ordered (Colhd) structure around 85 C. The role played by the long alkyl chains in the formation of the supramolecular hexagonal mesophase is emphasized by comparing these results with those obtained from an analogous polymer with dodecyl substituents which exhibits only the Colhd structure over the whole range of temperature explored.     

Inorganic membranes and solid state sciences

The latest developments in inorganic membranes are closely related to recent advances in solid state science. Sol–gel processing, plasma-enhanced chemical vapor deposition and hydrothermal synthesis are methods that can be used for inorganic membrane preparation. Innovative concepts from material science (templating effect, nanophase materials, growing of continuous zeolite layers, hybrid organic–inorganic materials) have been applied by our group to the preparation of inorganic membrane materials. Sol–gel-derived nanophase ceramic membranes are presented with current applications in nanofiltration and catalytic membrane reactors. Silica membranes with an ordered porosity, due to liquid crystal phase templating effect, are described with potential application in pervaporation. Defect-free and thermally stable zeolite membranes can be obtained through an original synthesis method, in which zeolite crystals are grown inside the pores of a support. Hybrid organic–inorganic materials with permselective properties for gas separation and facilitated transport of solutes in liquid media, have been successfully adapted to membrane applications. Potential membrane developments offered by CVD deposition techniques are also illustrated through several examples related to the preparation of purely inorganic and hybrid organic–inorganic membrane materials.