Example crystallization sodium salt

Heating peralkylated derivatives 56a in BBr3 leads selectively to the 6-bromo derivatives 56b via Br/alkyl exchange [74], Among other transformations, the reaction of 56b with the sodium salt of a thioazadiiron cluster is an example of combining main group and transition metal clusters in one molecule (56c), which provided crystals for structural characterization (Scheme 3.2-29) [75]. 

Several examples of carbenoid ion-radicals are discussed within this book. A silylene anion-radical preparation and properties is exemplified here. Scheme 2.5 shows the path to this species. Tetrakis(di-tert-butytmethylsilyl)disilylene was reduced by lithium or sodium salt of naphthalene anion-radical in THF at 78°C and then 12-crown-4 was added to the resulting reaction mixture. The silylene anion-radical was obtained as the corresponding alkali salt. Red crystals of the salt were isolated and characterized by ESR spectroscopy and x-ray crystallography (Inoue et al. 2007). 

A question which may sometimes be asked is this If an enantio-morphous crystal- -that is, one possessing neither planes, nor inversion axes, nor a centre of symmetry—is dissolved in a solvent, does the solution necessarily rotate the plane of polarization of light The answer to this question is, Not necessarily . If the molecules or ions of which the crystal is composed are themselves enantiomorphous, then the solution will be optically active. But it must be remembered that enantiomorphous crystals may be built from non-centrosymmetric molecules which in isolation possess planes of symmetry—these planes of symmetry being ignored in the crystal structure such molecules in solution would not rotate the plane of polarization of light. (A molecule of this type, in isolation, may rotate the plane of polarization of light (see p. 91), but the mass of randomly oriented molecules in a solution would show no net rotation.) An example is sodium chlorate NaC103 the crystals are enantiomorphous and optically active, but the solution of the salt is inactive because the pyramidal chlorate ions (see Fig. 131) possess planes of symmetry. 

An ionic compound typically contains a multitude of ions grouped together in a highly ordered three-dimensional array. In sodium chloride, for example, each sodium ion is surrounded by six chloride ions and each chloride ion is surrounded by six sodium ions (Figure 6.11). Overall there is one sodium ion for each chloride ion, but there are no identifiable sodium-chloride pairs. Such an orderly array of ions is known as an ionic crystal. On the atomic level, the crystalline structure of sodium chloride is cubic, which is why macroscopic crystals of table salt are also cubic. Smash a large cubic sodium chloride crystal with a hammer, and what do you get Smaller cubic sodium chloride crystals Similarly, the crystalline structures of other ionic compounds, such as calcium fluoride and aluminum oxide, are a consequence of how the ions pack together. 

Matter is composed of spherical-like atoms. No two atomic cores—the nuclei plus inner shell electrons—can occupy the same volume of space, and it is impossible for spheres to fill all space completely. Consequently, spherical atoms coalesce into a solid with void spaces called interstices. A mathematical construct known as a space lattice may be envisioned, which is comprised of equidistant lattice points representing the geometric centers of structural motifs. The lattice points are equidistant since a lattice possesses translational invariance. A motif may be a single atom, a collection of atoms, an entire molecule, some fraction of a molecule, or an assembly of molecules. The motif is also referred to as the basis or, sometimes, the asymmetric unit, since it has no symmetry of its own. For example, in rock salt a sodium and chloride ion pair constitutes the asymmetric unit. This ion pair is repeated systematically, using point symmetry and translational symmetry operations, to form the space lattice of the crystal. 

For example, when sodium sulfate crystallizes from aqueous solution below 40°C the crystals that form are anhydrous Na2S04, while above 40°C each molecule of Na2S04 that crystallizes has 10 molecules of water associated with it. The hydrated salt, Na2SO4T0H2O(s), is called sodium sulfate decahydrate. The change from the anhydrous to the hydrated form of the solid at 40°C is responsible for the discontinuity in the plot of Figure 6.5-1. Another solute that forms hydrated salts is magnesium sulfate, which can exist in five different forms in different temperature ranges. (See Table 6.5-1.)... 

Analysis of many different salts show that the salts all have ordered packing arrangements, such as those described earlier for NaCl and CaF2. Another example is the salt cesium chloride, where the ratio of cations to anions is 1 1 just as it is in sodium chloride. However, the size of a cesium cation is larger than that of a sodium cation. As a result, the structure of the crystal lattice is different. In sodium chloride, a sodium cation is surrounded by six chloride anions. In cesium chloride, a cesium cation is surrounded by eight chloride anions. The bigger cation has more room around it, so more anions can cluster around it. 

Most salts crystallize as ionic solids with ions occupying the unit cell. Sodium chloride (Figure 13-28) is an example. Many other salts crystallize in the sodium chloride (face-centered cubic) arrangement. Examples are the halides of Li+, K+, and Rb+, and M2+X2 oxides and sulfides such as MgO, CaO, CaS, and MnO. Two other common ionic structures are those of cesium chloride, CsCl (simple cubic lattice), and zincblende, ZnS (face-centered cubic lattice), shown in Figure 13-29. Salts that are isomorphous with the CsCl structure include CsBr, Csl, NH4CI, TlCl, TlBr, and TIL The sulfides of Be2+, Cd2+, and Hg2+, together with CuBr, Cul, Agl, and ZnO, are isomorphous with the zincblende structure (Figure 13-29c). 

EXAMPLE 8-2 Crystallization of the Sodium Salt of a Drug Candidate... 

The fifth example is the sodium salt of a-L-guluronic acid (23). In the crystal, two cations are coordinated to each sugar molecule one to O-1,0-2, and 0-3 and another to 0-4,0-5, and one of the carboxylate oxygen atoms. However, the Na-O-2 and the Na-0-5 distances (285 and 272 pm) are larger than the others, and it is not certain that they represent coordination. 

While there are several examples of metal complexes which are amphiphilic in nature, it is in very few cases that lyotropic liquid crystals mesophases have been characterized. Although numerous and strictly classifiable as metallomesogens, in this article we exclude discussion of the amphiphiles with a simple metal ion as the cation (e. g. sodium salts of carboxylic acids), rather concentrating on amphiphiles in which the metal cation is an integral part of the amphiphile. 

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