Salt-inclusion solids

Another novel strategy for synthesising and designing NCS materials has been described by Hwu et He has focused on salt-inclusion solids 

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Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

The new phases were discovered by the combination of exploratory synthesis and a phase compatibility study. As commonly practised, the new studies were initially made through the chemical modification of a known phase. Inclusion of salt in some cases is incidental, and the formation of mixed-framework structures can be considered a result of phase segregation (for the lack of a better term) between chemically dissimilar covalent oxide lattices and space-filling, charge-compensating salts. Limited-phase compatibility studies were performed around the region where thermodynamically stable phases were discovered. Thus far, we have enjoyed much success in isolating new salt-inclusion solids via exploratory synthesis. 

Over the last few years, we have made a number of novel discoveries using reactive salt fluxes in the crystal growth experiment of mixed-metal oxides. The most important outcome that these salt-inclusion solids have demonstrated is the propensity for structure- directing effects of the employed salt. These hybrid solids have revealed fascinating solid-state structures ranging from nanoclusters to three-dimensional open frameworks of current interest. Solids featuring mag-... 

Based on the concept of mixed-framework lattices, we have reported a novel class of hybrid solids that were discovered via salt-inclusion synthesis [4—7]. These new compounds exhibit composite frameworks of covalent and ionic lattices made of transition-metal oxides and alkali and alkaline-earth metal halides, respectively [4]. It has been demonstrated that the covalent frameworks can be tailored by changing the size and concentration of the incorporated salt. The interaction at the interface of these two chemically dissimilar lattices varies depending upon the relative strength of covalent vs. ionic interaction of the corresponding components. In some cases, the weak interaction facilitates an easy... 

To demonstrate the utilities of salt inclusion, we review the selected zeoUte-like transition-metal-containing open frameworks (TMCOFs) and then describe the structures of non-centrosymmetric solids (NCSs) and, finally, report crystalline solids containing a periodic array of transition metal nanostructures. In particular, we will address the issues concerning the role that molten salt has in... 

It is obvious from the preceding discussion that salt and solid form selection are intertwined. The propensity of a compound, either neutral or a salt, to exist in different crystal forms is considered as part of the salt selection process. However, once selected for inclusion in drug product, the solid-state properties of a given compound must be evaluated in detail. The following section describes the solid-form selection process as it is carried out with a single chemical entity. 

In contrast to 1, the related pure host 7 may be obtained in crystalline form 68). The crystal structure of 7 is built via helical chains of alternating intra- and inter-molecular H-bonding through the carboxyl functions. This structure supplies the information that the carboxyl groups are therefore already positioned in an appropriate way to facilitate analogous H-bonding in the known inclusions of 7. As discussed later (Sect. 4.2.2), these are exclusively salt-type associates and as such, intimately interact with the carboxyl groups. Hence one may infer that displacement of the carboxyl functions from position 2 in 1 to position 8 in 7 reduces the ability of inclusion formation. Similar reasons such as the solid-solubility differences observed in the classical naphthalene/chloronaphthalene systems (alpha- vs. beta-substituted derivatives, cf. Ref. 28 may also be applied here. 

Figure 9 shows a relationship between JTl and JTsc,ov for all salts. Any relationship between them is not clear on the whole. However, inversely proportional relationships are slightly observed for each group of barium salts and sodium salts. Considering such experimental result, it may be supposed that the adhesion force of remained clusters is controlled by more strong factors, such as a crack of the surface of nucleation agent occurred by the solid inclusion during the activation treatment. 

A number of modified reaction conditions have been developed. One involves addition of silver salts, which activate the halide toward displacement.94 Use of sodium bicarbonate or sodium carbonate in the presence of a phase-transfer catalyst permits especially mild conditions to be used for many systems.95 Tetraalkylammonium salts often accelerate reaction.96 Solid-phase catalysts in which the palladium is complexed by polymer-bound phosphine groups have also been developed.97 Aryl chlorides are not very reactive under normal Heck reaction conditions, but reaction can be achieved by inclusion of triphenylphosphonium salts with Pd(OAc)2 or PdCl2 as the catalyst.98... 

The method relies on the p and n salts having different solubilities, and they must not form solid solutions or double salts. The more insoluble salt is filtered and the purified acid recovered by adding mineral acid. This method of chiral resolution is well established, and lists of resolving agents for many classes of racemic compounds are available [22], Inclusion chemistry may be employed for the same purpose by preparing host-guest compounds with a chiral host ... 

The term semi-clathrate refers to solid inclusion compounds where, in addition to non-bonded, clathrate interactions, there is a contribution of chemical bonding. In the example used above, this chemical contribution is of ionic nature fluoride anion from the ammonium salt is incorporated into the water host framework linked via hydrogen bonds. Thus, the host has anionic character and guest-host interactions have ionic component. 

Typically, the resin (which had to be hydrophilic) was swollen and stirred in a solution containing the salt mixtures coding for a particular monomer of one of the sets. A thorough washing was done to eliminate the non-absorbed salts and to avoid cross-contamination of other beads during the mix and split operations. The mechanism by which the salts remained bound to the solid support was not determined possibilities such as complex formation or inclusion effects were mentioned, and the use of resins containing heteroatomic... 

Two calix[4](diseleno)crown ethers were synthesized by the treatment of the disodium salt of 1,3-propanediselanol with preorganized 1,3-dibromoethoxycalixarenes the 1,3-Se-bridged calixarene forms an infinite sheet aggregate by means of self-inclusion and intermolecular Se—Se interactions in the solid state <02TL131>. 

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