Saltlike

Von Baeyer (Nobel Prize, 1905) should be credited for having recognized in 1902 the saltlike character of the compounds formed. He then suggested a correlation between the appearance of color and salt formation—the so-called halochromy. Gomberg (who had just shortly before discovered the related stable triphenylmethyl radical), as well as Walden, contributed to the evolving understanding of the structure of related cationic dyes such as malachite green. 

Bismuthides. Many intermetaUic compounds of bismuth with alkafl metals and alkaline earth metals have the expected formulas M Bi and M Bi, respectively. These compounds ate not saltlike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi . Both the alkafl and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particularly noteworthy as having extremely short bond distances between the alkafl metal atoms. 

Saltlike Carbides. Almost all carbides of Groups 1—3 of the Periodic Table are saltlike. Beryllium carbide and Al C may be considered as derivatives of methane ion) and most carbides having C2 groups, ie, ions, as derivatives of acetylene. This is supported to some extent by hydrolysis reactions ... 

The nature of a binary hydride is related to the characteristics of the element bonded to hydrogen (Fig. 14.8). Strongly electropositive metallic elements form ionic compounds with hydrogen in which the latter is present as a hydride ion, H. These ionic compounds are called saline hydrides (or saltlike hydrides). They are formed by all members of the s block, with the exception of beryllium, and are made by heating the metal in hydrogen ... 

Carbon is the only Group 14/IV element that forms both monatomic and polyatomic anions. There are three classes of carbides saline carbides (saltlike carbides), covalent carbides, and interstitial carbides. The heavier elements in Group 14/IV form polyatomic anions, such as Si44 and Sn52, in which the atoms form a tetrahedron and trigonal bipyramid, respectively. 

This event is clearly demonstrated by the behavior of 4-cyanopyridine which forms an adduct even with an excess of tribromoborane. However, 4-cyano-pyridinium chloride yields a saltlike dimeric iminoborane derivative 26> as depicted in Eq. (17). 

Saltlike carbides, 4 647, 648-650 Salt-like nitrides, 77 198-199 Salt mines, 22 799, 800 Salt-out, general separation heuristics for, 22 320... 

Surface compounds other than saltlike compounds on the surface of silica-alumina would not be expected to be very stable due to the strong surface acidity. Traces of water would decompose such compounds. 

We now return to the consideration of the other reactions in Table IV. If the parent ion radical decomposes by losing a hydrogen atom a carbonium ion remains. The main characteristic of the carbonium ion is its strongly acidic character and the formation of saltlike complexes.32 This is another extension of the isoelectronic principle, and is illustrated in reactions 4 and 5 of Table IV. The carbonium ion, CH3+, may be envisioned as forming a three-center transition complex... 

Saltlike metal catalysts without hydrophilic phosphane ligands can be used for reactions in water. For example, aqueous RuC13 and Pd(edta) are water soluble, and many other metal complexes that coordinate water as a ligand are soluble in water (60). These metal complexes have one important disadvantage when they are used as catalysts in water. It is the problem of leaching, which means that the catalyst can be extracted from the aqueous phase into the organic or product phase. The hydrophilicity of a metal salt or an ionic complex is not high, and so polar products may coordinate and transport them into the second phase. This topic is not considered in this review a summary was reported by Kalck and Monteil (2). A recent book about this subject was written by Martell and Hancock (61). 

The atoms listed in this section may combine with many metals to form binary compounds (compounds made up of two elements) that are saltlike in nature, but are not derived from acids. For purposes of naming, it is convenient to assign negative charges to these atoms. Except in the names of the oxides, the suffixes -ous and -ic are not used with metals forming compounds in this group. The names of all these compounds end in -ide. Only the metal oxides of this... 

Lower temperature favors the sublimation of ammonium chloride vapor to a white saltlike solid. 

CARBIDES. A binary solid compound of carbon and another element. The most familiar carbides are those of calcium, tungsten, silicon, boron, and iron (cemcntitc) Two factors have an important bearing on the properties of carbides (1) the difference in electronegativity between carbon and the second elemenl. and (2) whether the second element is a transition metal. Saltlike carbides of alkali metals are obtained by reaction with acetylene. Those ohlained from silver, copper, and mercury sails are explosive. See also Carbon and Iron Metals, Alloys, and Steels. 

In the next section, we review some general chemistry regarding saltlike and covalent compounds that will be of special relevance to our later discussions. 

Why is carbon so versatile in its ability to bond to very different kinds of elements The special properties of carbon can be attributed to its being a relatively small atom with four valence electrons. To form simple saltlike compounds such as sodium chloride, Na Cle, carbon would have to either lose the four valence electrons to an element such as fluorine and be converted to a quadripositive ion, C4 , or acquire four electrons from an element such as lithium and form a quadrinegative ion, C40. Gain of four electrons would be energetically very unfavorable because of mutual repulsion between the electrons. 

Lithium hydride can be regarded as a saltlike ionic compound, Li H. Electrostatic attractions between oppositely charged ions in the crystal lattice... 

The beryllium chelate of 2,4-pentanedione is another example of a stable chelate it melts at 108°, boils at 270°, and is soluble in many organic solvents. By replacing the methyl groups of 2,4-pentanedione with rert-butyl groups, a diketone is obtained which, with many metals including transition and rare-earth metals, forms complexes that often are highly soluble in nonpolar organic solvents. The interior of these chelates is saltlike but the exterior is hydrocarbonlike and nonpolar, which accounts for the substantial solubility in nonpolar solvents. 

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