Sodium salt crystal structure

FIGURE7.4 The rock salt or sodium chloride crystal structure. 

The ionic hydrides are white solids with high melting points, and all of the alkali metal hydrides have the sodium chloride crystal structure. Because they resemble the salts of the alkali and alkaline earth metals, the ionic hydrides are often referred to as saline or salt-like hydrides. The properties of the alkali metal hydrides are shown in Table 6.3, and those of the alkaline earth hydrides are shown in Table 6.4. 

Two very simple descriptions of the rock salt crystal structure are also given. According to one, the sodium and chloride ions occupy positions with point-group symmetry m3m forming a checkered pattern in the Fm3m space group. According to the other description, the structure consists of two cubic sublattices in parallel orientation, one of sodium ions and the other of chloride ions. 

Perhaps the most common AX crystal structure is the sodium chloride (NaCl), or rock salt, type. The coordination number for both cations and anions is 6, and therefore the cation-anion radius ratio is between approximately 0.414 and 0.732. A unit cell for this crystal structure (Figure 12.2) is generated from an FCC arrangement of anions with one cation situated at the cube center and one at the center of each of the 12 cube edges. An equivalent crystal structure results from a face-centered arrangement of cations. Thus, the rock salt crystal structure may be thought of as two interpenetrating FCC lattices—one composed of the cations, the other of anions. Some common ceramic materials that form with this crystal structure are NaCl, MgO, MnS, LiF, and FeO. 

The crystal structure of the sodium salt of 30 (NAMI) is shown in Fig. 9, where Na(I) bridges two molecules of 30 via oxygens of S-bound DMSO and water. This complex may be readily reduced in vivo (E1/2, -0.001 V) (166), whereas the bis-imidazole complex 28 has a lower redox potential and is more difficult to reduce. The reduction potential of 28 is strongly pH dependent (AE = —118 mV/pH unit near pH 7), reduction being more favorable at acidic pH values (167). This complex hydrolyses at a similar rate to cisplatin (ty ca. 3 h at 310 K) and, like cis-platin, aquation appears to be necessary for DNA binding (168). 

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]. 

The other change that needed to be made in the synthesis of RSR 13 for in vivo administration was the method of purification. RSR 13 is used in vivo as the sodium salt. I prepared the first batch for in vivo toxicology by triturating RSR 13 sodium salt with acetone to remove any vestiges of water. However, the first industrial scale-up procedure called for crystallization of the salt from ethanol-water. The ethanol-water crystals were not as soluble as the acetone triturated method and could not be formulated at a reasonable volume. We performed the crystal structure determination of the ethanol-water crystals and found that it was a heptahydrate (Figure 17.5) [50]. The problem for large-scale production of RS R13 was solved eventually by the industrial producers of RSR 13. 

Saeo, M.K. and Abraham, D.J. Crystal Structure of Rsr 13 Sodium Salt Hepta-Hydrate. 2004, Unpublished data. 

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