Saltlike halides

I) saltlike halides according to the formulation (R +)(X )2 with typically ionic crystal structures and... 

The second example shows that such a reaction need not always lead to an uncharged system. If, instead of thiocarbene complexes, amino-carbene complexes are treated with hydrogen halides, products of saltlike character are isolable (66). One finds the halogen at the metal and the hydrogen at the removed carbene ligand, and one obtains iminium halo-genopentacarbonylmetalates ... 

All of the binary tetrahalides of carbon, silicon, germanium, and tin have been made, and many mixed halides (of the type SiCl2F2) have also been characterized. Except for SnF4 (the most saltlike of the group), all of the tetrahalides are volatile. It is interesting (and not easily explained) that aside from CF4 and SiF4, the tetrahalides of silicon boil at lower temperatures than those of carbon. 

Thus, owing to the endothermic character of the H" ion, only the most electropositive metals—the alkalis and the alkaline earths—form saline or saltlike hydrides, such as NaH and CaH2. The ionic nature of the compounds is shown by their high conductivities just below or at the melting point and by the fact that on electrolysis of solutions in molten alkali halides hydrogen is liberated at the anode. 

All of the alkaline earth metals form saltlike MX2 dihahdes (see Alkaline Earth Metals Inorganic Chemistry). Within this group, we observe stmctural effects owing to both cation sizes and properties of the halide ions. From Be to Ba, coordination numbers monotonically increase from four (tetrahedral) in Be dihalides to eight (cubic) or nine (tricapped trigonal prismatic) in the Ba systems. 

Reference has already been made in several places to the remarkable observation that halides of the same composition may occur in both a molecular and a saltlike form (98). In some cases the two forms exist side by side (e.g., PCl2Fr[PCl4][PF6]) or can be observed together (PC14F-[PC14]F). A similar phenomenon has been observed in the organic field, e.g.,... 

Michaelis and Kaehne isolated a product with saltlike properties from the reaction of triphenyl phosphite and methyl iodide. This observation has been confirmed by Arbuzov and Sazonova (30) and by Landauer and Rydon (206,284), who used this salt as a reagent for the preparation, in excellent yields, of alkyl halides, including neopentyl iodide, from the corresponding alcohols. The course of this reaction... 

The saltlike alkali metal compounds of indole react with electrophiles such as haloalkanes, acyl halides, sulfonyl halides and trimethylchlorosilane to form the corresponding 1-substituted indoles. 1-Benzylindole isomerizes to 2-benzylindole when heated in polyphosphoric acid [47]. 1-Phenyl-sulfonylindole is lithiated in the 2-position by n-butyllithium. Subsequent alkylation with haloalkanes and cleavage of the phenylsulfonyl residue with sodium hydroxide yields 2-alkylindole. 

In the reduced binary and ternary halides of the lanthanoids, the f electrons are well localized on the metal atoms. The coupling between the magnetic moments is weak in the case of insulators as can be seen from the low ordering temperatures of the saltlike trihalides whereby, for example, GdQj orders ferromagneti-cally at 2.2K. In the presence of extended M-M bonding, the conduction electrons provide a very efficient mechanism for coupling the moments via a RKKY... 

The pattern as seen in Figure 5 may be transferred to a periodic table of the rare earth elements, see Figure 6. Only elements underlaid in red form clusters. The lower I3 is, the easier it is to produce cluster complexes. Elements underlaid in blue form stable divalent compounds, for example EUCI2 the divalent state with the electronic configuration 4f 5d° (with n =7, 14, 6, 13 for R = Eu, Yb, Sm, Tm) has the highest stability and, thus, is the easiest to achieve when the third ionization potential is the highest. The divalent chemistry of these elements is alkaline-earth and saltlike this is described in The Divalent State in Solid Rare Earth Metal Halides. 

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