Low-temperature solid-state

Low-temperature solid-state synthesis is preferred in most cases, where appropriate, for obvious reasons such as energy and cost economy and process safety or for critical concerns regarding the accessibility of compounds that are stable only at low temperatures or non-equilibrium phases, i.e., compounds thermodynamically unstable with respect to the obtained phase (e.g., a ternary instead of binary phase). The use of low-temperature eutectics as solvents for the reactants, hydrothermal growth... 

Stereochemistry. - There has been a far infra-red spectroscopic study of ethyl phosphine,130 and in combination with X-ray fluorescence, further work completed on the conformational analysis of dialkylphenyl phosphines.131 The influence of water on the conformational equilibria of trimethyl phosphate has received attention.132 There has been a low temperature solid state and matrix isolation study of methyl phosphorodichi oridate,133 and a conformational study of polymorphic modifications of diphenyl-phosphinyl acetic acid hydrazide. 34... 

A. S. Lipton, R. W. Heck, J. A. Sears and P. D. Ellis, Low temperature solid-state NMR experiments of half-integer quadrupolar nuclides caveats and data analysis. /. Magn. Reson., 2004,168, 66-74. 

P. D. Ellis and A. S. Lipton, Low-temperature solid-state NMR spectroscopy a strategy for the direct observation of quadrupolar nuclides of biological interest. Annu. Rep. NMR Spectrosc., 2006, 60,1-38. 

Simultaneous evaporation of metal with organic and inorganic substances followed by vapor deposition on a substrate allows the production of composite films containing M nanoparticles stabilized in various dielectric matrices [2, 28]. The use of monomer molecules in this process polymerizing during deposition or as a result of the subsequent reactions yields polymeric nanocomposite films with metal inclusions [2, 3, 28, 37]. The new low-temperature synthesis of polymeric nanocomposite films has been elaborated recently. This synthesis is based on the deposition of M/SC and monomers vapors at temperature 80 K followed by low-temperature solid-state polymerization of obtained films in conditions of frozen thermal movement of molecules (cryochemical synthesis) [2], This synthesis has important features, which will be considered further. 

As mentioned above, the new method of cryochemical synthesis of polymer nanocomposite films has been developed based on co-deposition of M/ SC and monomer vapors at temperature 80K and subsequent low-temperature solid-state polymerization of monomer matrix ([2] and works cited herein). It has been established that a number of monomers (acrylonitrile, formaldehyde, /i-xylylene and its derivatives) polymerize in solid state in absence of thermal movement of molecules owing to own specific supra-molecular structure. When reaction is initiated by y- or UV-radiation the formation of a polymer matrix occurs even at the temperatures close to temperature of liquid helium [66-69]. 

As shown by experiments, the approach employed has proved its value, the initial premises have been found to be right, and the study has led to the discovery of highly active autowave regimes of low-temperature solid-state conversion, which became the subject of the entire series of studies. 

I. M. Barkalov, V. V. Barelko, V. I. Goldanskii, D. P. Kiryukhin. and A. M. Zanin, Threshold Phenomena and Autowave Processes in Low-Temperature Solid-State Chemical Reactions , preprint, Inst. Chem. Physics AN SSSR, Chernogolovka (1983) (in Russian). 

B1U Aig) systems, observed under low resolution in the vapor phase, are displayed in Fig. 2 19>. It is apparent that, despite the low spectral resolution, bandwidths in the latter system are very considerably greater. This relative characteristic is not lost in the low-temperature solid-state spectra where in the crystal at 4 K linewidths as small as 1 cm-1 are obtained for the first singlet system 2°), compared to greater than 100 cm-1 for the second system 21,22). jn a krypton matrix linewidths of 10—35, 300 and 350 cm-1 are recorded for the first three Tin systems, respectively 23>. 

Another interesting aspect one may encounter in low-temperature solid-state photolysis is the phenomenon of pairwise trapping of two identical radicals formed by the photodecomposition of a single molecule. For example, photolysis of solid azobisisobutyronitrile at 77°K leads to pairwise trapping of two radicals separated... 

Development of the Notions about the Mechanism of Low-Temperature Solid-State Reactions... 

The current status of the models of fluctuational and deformational preparation of the chemical reaction barrier is discussed in the Section 3. Section 4 is dedicated to the quantitative description of H-atom transfer reactions. Section 5 describes heavy-particle transfer models for solids, conceptually linked with developing notions about the mechanism of low-temperature solid-state chemical reactions. Section 6 is dedicated to the macrokinetic peculiarities of solid-state reactions in the region of the rate constant low-temperature plateau, in particular to the emergence of non-thermal critical effects determined by the development of energetic chains. 

DEVELOPMENT OF THE NOTIONS ABOUT THE MECHANISM OF LOW-TEMPERATURE SOLID-STATE REACTIONS... 

The evaluation made in the preceding section shows the possibility of a natural explanation of the regulation of low-temperature solid-state reactions in a model accounting for barrier parameter oscillations resulting from intermolecular vibrations. A consistent analysis of such a model is required. A mathematical body used for this purpose is, conceptually, close to the common theory of nonradiative transitions, but unlike the latter it enables us to exceed the limits of the one-dimensional Franck-Condon approximation which is inapplicable in treatment of heavy-particle transfer. 

As we have seen, the expressions for the rate constant obtained for different models describing the lattice vibrations of a solid are considerably different. At the same time in a real situation the reaction rate is affected by different vibration types. In low-temperature solid-state chemical reactions one of the reactants, as a rule, differs significantly from the molecules of the medium in mass and in the value of interaction with the medium. Consequently, an active particle involved in reaction behaves as a point defect (in terms of its effect on the spectrum and vibration dynamics of a crystal lattice). Such a situation occurs, for instance, in irradiated molecular crystals where radicals (defects) are formed due to irradiation. Since a defect is one of the reactants and thus lattice regularity breakdown is within the reaction zone, the defect of a solid should be accounted for even in cases where the total number of radiation (or other) defects is small. 

These results further demonstrate the ability of very low temperature solid-state NMR methods to differentiate rapidly equrtibrating classical ion systems from nonclassical bridged systems, even when the equilibration barrier involved is much less than 3 kcal mol... 

Solid state chemistry plays an important role in the catalysis by Transition Metal Sulfides however, it is a role that is somewhat different than the role usually assigned to solid state chemistry in catalysis. In catalysis, by sulfides, the chemistry of ternary phases is not now important and thus, the usual role of solid state chemistry in preparing ternary phases and systematically studying the effect on catalytic properties through variation of the composition of these ternary phases is absent. Nevertheless, preparation of the Transition Metal Sulfides is crucial in controlling the properties of the catalysts. Low temperature solid state preparations are the key to obtaining good catalysts in reasonable surface area for catalytic measurements. 

Here x and x are column vectors of the components x (t) and x (t), respectively, and A(t) is now a physical reaction matrix containing time-dependent elements. Fluorescence of kinetic transients, e. g., the relaxation profiles of monomer- or excimer fluorescence are, therefore, strictly nonexponential for which closed form, analytical solutions can be found in few cases, only. A convincing manifestation of nonexponential trapping in low-temperature, solid state p-N-VCz is a recent analysis by Bassler et al. (4, ). With the use of rate function in Equation 2, the transient ps-rise profile of the low-energy excimer E2 has been satisfactorily fitted to the numerical solution of Equation 3 with a single-fit dispersion parameter a between 0.2 and 0.8 depending on the temperature of the system. 

Complexes [ZnX(Tp,Bu,Me)] (X = Br, Cl, and OH) have been investigated by low-temperature solid-state 67Zn NMR spectroscopy. The value of the quadrupole coupling constant Cq for the zinc increased monotonically with the electronegativity of X, e.g. Br < Cl OH.102... 

Ammonium halides have been used as versatile reagents in low-temperature solid-state redox and acid-base reactions. For example, direct reaction with the appropriate metal at 270-300° yields the ammonium salts of ZnClq , LaCls ", YCl6 , YBre, CuCb , etc., whereas Y2O3 yields either (NH4)3YBr6 or YOBr depending on the stoichiometric ratio of the reagents. Solid-state reactions of ammonium sulfate, nitrate, phosphates and carbonate have also been studied. 

Gas-phase infrared and low-temperature solid-state infrared and Raman spectra were obtained for Np(BHt+)i+ and Np(BDi+)i+ from 2.5 to 50y. Assignments were made of the observed bands and the fundamental frequencies were fitted to calculated values in a normal coordinate analysis (10). 

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