Solid solutions adaptive compounds

FIGURE 7.23 A more complicated solid solution phase diagram. This is for the Na/K system. This phase diagram shows the existence of a stoichiometric compound, NajK. Source Adapted from T. M. Duncan andj. A. Reimer, Chemical Engineering Design and Analysis An Introduction, Cambridge University Press, 1998. 

FIGURE 6.17 Conductivity of some proton conductors as a function of 1/T. The overlapping area between BaCeOj and SrCeOj indicates solid solutions based on these compounds. (Adapted from Iwahara, H., Bull. Ceram. Soc. Jpn., 1992, 27, 112. With permission.)... 

Receiver adapters, 212t Recrystallisation, 122-125 common solvents for, 124 choice of solvent for, 125, 232 difficulties encountered in, 129, 130 exercises in, 232, 233 experimental details for, 125-127 61tration of hot solutions in, 126 less common solvents for, 124 in an atmosphere of inert gas, 135 purification of solid compounds by, 232, 233... 

Compounds containing the (hydroxy)ethyleneamino link 8 were originally prepared in solution by reduction with NaBH4 of the carbonyl in the oxomethyleneamino link 7. 141,155,156 This reaction was later adapted to solid-phase conditions. 150,159 Two diastereomers, differing in the chirality of the hydroxylated carbon, have been characterized and their absolute configuration assigned by X-ray diffraction in some cases, 149156 but their separation is usually not possible. 142 ... 

The objective of improvement schemes is to study and validate each step of different analytical procedures applied by different laboratories in a collaborative manner. Such programmes usually involve groups of 20-50 laboratories. In the best case, each critical step of the procedure should be evaluated in an adapted exercise. The individual steps may be studied with a series of different materials in a stepwise manner. In principle the strategy consists of starting from the simplest matrix, e.g. pure solutions and/or mixtures of compounds in solution, for testing the performance of the detector. The analysis of more complex matrices (e.g. raw extract, purified extract) enables the separation and/or clean-up steps to be tested, whereas solid samples are used to test the entire procedure. Spiked samples can be analysed to evaluate the extraction procedure, within the limits of this evaluation (as commented in Section 2.3.1). Such an approach is actually similar to the steps that should be followed when developing and validating a new method in a laboratory. 

We report here some results of an exploratory project on the HDN activity of [M(PC) ] where M represents a variety of metals. We have chosen first to study the model compound quinoline. The [M(PC)] catalyst were supported on high surface area inorganic oxides to produce heterogenized catalysts. The solid catalysts are convenient to study because of the ease of separation and process adaptability. Further, due to the low solubility of [M(PC)] in almost all solvents, the high surface area supported catalysts are expected to have a considerably higher effective concentration of [M(PC)] than the small portion of [M(PC)] that is in homogeneous solution or the low surface area solid [M(PC)]. 

Various fluorides may be precipitated from aqueous solution for use as constituent powders in solid state reactions. Co-precipitation offers very elegant access to intimate mixtures, but the actual products are strongly dependent on the fluoride ion activity within the solution but also on the stability constants of the respective metal complexes. Accordingly, not only anhydrous fluorides are obtained, but also hydrated fluorides or hydroxide fluorides, which may be very difficult to convert to pure fluorides. As noted already [3], reactive compounds, e.g. carbonates, acetates, oxalates, hydroxides etc., which quite easily dissolve in acidic HF solutions, are the preferred starting materials for fluoride syntheses. In contrast, many oxides which have been heated to rather high temperature are frequently unreactive and may not dissolve at all. To enhance reactivity but also improve crystallinity of the product, it has proved useful to perform reactions above the boiling point of water in adapting the hydrothermal method, which has already been shown to be useful in the recrystallisation of materials which are more or less insoluble at ambient temperatures and pressures. Up to about 240°C even PTFE vessels may be used. A number of selected examples with respective reaction conditions are listed in Table 3. 

Fipire 10 111.9 MHz solid state CP/MAS " Sn NMR spectrum of an 1,2,5-oxoniastannaboratole (adapted with permission from Ref. [26]). The expansion of the centre bands (mark by arrows) reveals a resolv pattern according to V(" n"B)=S5 10Hz which is not resolved in the " Sn NMR spectra of solutions of the same compound. The " /" Sn satellites (asterisks), corrcspondng to V(Sn,Sn) 1930 Hz, are also readily observed. Since this parameter should be sensitive even to small structural changes, it aiq)eaTS that the solid state structure differs little from the structure in solution /( n, n)=20S0Hz)... 

Fluorous chemistry integrates the characteristics of solution-phase reactions and the phase tag strategy developed for solid-phase chemistry [7-15], Perfluoroalkyl chains instead of polymer beads are used as the phase tags to facilitate the separation process. In 2001 the Curran group first reported the concept of fluorous mixture synthesis (FMS) for solution-phase library synthesis [16], FMS is able to produce individual pure compounds without the effort of deconvolution. It adapts literature procedures to synthesize complex natural products, their enantiomers and diastereomers. FMS can also be used for the development of new synthetic protocols and to make novel drug-like molecules [17, 18],... 

One of the most time-consuming steps in synthesis on solid supports is the adaptation and optimization of reaction conditions. Furthermore, the optimization process is difficult to monitor on the solid support. Magic-angle spinning NMR (MAS) or FT-IR can be used, but these are technically very demanding. A possible solution is the concept of dual linkers involving an analytical unit [200]. These can be employed not only to optimize chemical reactions on a support, but also for quality control of the compound libraries. The basic principle is outlined in Fig. 15. 

All the cited literature references to the above compounds have described solid-state syntheses at temperatures of 700-1200°. Such synthesis conditions will always lead to pyrochlore structure compounds in which all of the octa-hedrally coordinated sites are occupied by the noble metal cation, thus requiring the post-transition metal to noble metal molar ratio always to be 1.0. This paper focuses on solution medium syntheses at quite low temperatures (<75°), thereby stabilizing a new class of pyrochlore compounds in which a variable fraction of the octahedrally coordinated sites are occupied by post-transition element ca-tions.5,6 The specific example here involves the Pb2[Ru2 Pb4+]06 s series. The synthesis conditions may be simply adapted, however, to accommodate preparation of a wider range of pyrochlores which can be described by the formula A2[B2 xAx]07.3> where A is typically Pb or Bi, B is typically Ru or Ir and 0 < 1, and 0 < 1. 

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