Silver pseudohalides

The reaction of perfluorohalogenoalkanesulfenyl halides with silver pseudohalides leads to a group of compounds capable of undergoing a host of chemical changes. The first substances prepared in this way were the derivatives of trifluoromethanesulfenyl chloride (28) ... 

When reacting fiuorocarbonyl sulfenyl chloride with silver pseudohalides (66, 67), it is observed that it reacts only monofunctionally in contrast to the bifunctional chloro compound, e.g., o o... 

Diaryl tellurium chloride iodides precipitate silver chloride when treated with one equivalent of a silver pseudohalide and form diaryl tellurium iodide pseudohalides1,2. With two equivalents of silver pseudohalides, diaryl tellurium dipseudohalides are produced1-2. 

Diphenyl tellurium iodide cyanate slowly decomposes even at low temperature1. Surprisingly, when diaryl tellurium chloride iodides were stirred with equimolar amounts of silver pseudohalides in chloroform, silver chloride was surprisingly precipitated instead of the more insoluble silver iodide. The diaryl tellurium iodide pseudohalides were isolated in almost quantitative yields12. 

The following compounds were prepared similarly using the appropriate silver pseudohalide ... 

When diaryl tellurium halide pseudohalides are stirred in chloroform with silver pseudohalides, diaryl tellurium dipseudohalides with the same or different pseudohalides are formed1,3. 

Triphenyl telluronium chloride11 or methyl diphenyl telluronium iodide12 dissolved in hot water precipitated the corresponding telluronium pseudohalide when mixed with an aqueous solution of an alkali metal or silver pseudohalide. 

Only two representatives of this class of tellurium eompounds are known. They were prepared in quantitative yields from diphenyl tellurium iodide cyanide and silver pseudohalides. ... 

Dichlorosilicon phthalocyanine (XIX) is prepared from silicon tetrachloride and phthalonitrile in quinoline at 200°C 168,170). The blue-green crystals, which sublime readily at 430°C in vacuo, hydrolyze forming dihydroxysilicon phthalocyanine (XX) when refluxed with equal volumes of pyridine and aqueous ammonia (200). The corresponding difluorosilicon phthalocyanine is resistant to hydrolysis. Conversion of the chloride to the corresponding dicyanate, dithiocyanate, and diselenocyanate occurs upon reaction with the appropriate silver pseudohalide (178). The complexes are believed to involve nitrogen to silicon bonding in the case of the thiocyanate and selenocyanate. 

The greater reactivity of the P-X bond compared with the P-F bond is also evident from metathetical reactions with silver pseudohalides 105, 274) and silver salts of perfluorinated carboxylic acids 105), e.g.,... 

The most common compound of carbon and nitrogen is cyanogen, (CN)2. The cyanide ion, CN , is a pseudohalide ion, which means that it resembles a halide ion because it forms an insoluble silver compound and it can be oxidized to the X2 species. Cyanogen was first obtained by Gay-Lussac in 1815 by heating heavy-metal cyanides. 

There is an extensive chemistry associated with coordination compounds containing azide ions as a ligands. Like CN-, the azide ion is a pseudohalide ion, which means that it forms an insoluble silver salt, exists as the acid H-X, X-X is volatile, and it can combine with other pseudohalogens to give X-X. Although other pseudohalogens such as (CN)2 result from the oxidation of the CN- ion,... 

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

As shown in the introduction, the DNM anion can be regarded as a resonance stabilized, nonlinear planar pseudohalide, which forms an insoluble, highly explosive brownish silver salt upon addition of silver nitrate to an aqueous solution of 7. The DNM anion is related to the linear fulminate ion (CNO ) and can formally be regarded as the addition product of NO to fulminic acid (HCNO). Starting from CH4, NO containing nonlinear pseudohalides can be derived by successive substitution of H by NO, e.g. H3C(NO)/H2C(NO), H2C(N0)2/HC(N0)2 and HC(NO)3/C(NO)3, whereas the linear pseudohalide CNO is formally formed by replacing three H atoms by one NO unit and deprotonation. 

Table 25 Distances (pm) in some Silver Halide (or Pseudohalide) Phosphines (for Ag—X and X—X, the maximum and minimum values are given if available)...

The cyanide ion is called a pseudohalide ion because it behaves like Cl- in forming an insoluble, white silver salt, AgCN. In complex ions such as Fe(CN)63-, CN - acts as a Lewis base (Section 15.16), bonding to transition metals through the lone pair of electrons on carbon. In fact, the toxicity of HCN and other cyanides is due to the strong bonding of CN- to iron(III) in cytochrome oxidase, an important enzyme involved in the oxidation of food molecules. With CN attached to the iron, the enzyme is unable to function. Cellular energy production thus comes to a halt, and rapid death follows. 

Other coordination modes in pseudohalide complexes are comparatively rare. Amongst them, we note the structure of complex [AgLSCN] 0.25L (L = bipy), in which two silver ions are simultaneously bound with N atoms from NCS groups [166], The pseudohalide complexes with simultaneous different kinds of coordination of the NCS group are also rare. In particular, the complex compound [CuL(HL)2][Cu(L)(SCN)(p-NCS)], where LH is 2-dimethylaminoethanol, contains within its coordination sphere both kinds S-terminal (108) and -bridge (109) thiocyanate groups [178],... 

Diorganotetrapseudohalotellurates(IV) were obtained from tetrachlorotellurates(TV) or tetraiodotellurates(IV) via exchange reactions1 2. Silver cyanide was used to exchange chloride for cyanide1. Chloride and iodide were replaced by pseudohalides in reactions with potassium cyanate, potassium thiocyanate, or potassium azide. 

The azide ion is a good ligand, and it forms numerous complexes with metal ions. Chlorazide (C1N3) is an explosive compound prepared by the reaction of OCT and N3. As in the case of CN, the azide ion is a pseudohalide ion. Pseudohalogens are characterized by the formation of an insoluble silver salt, the acid H-X exists, X-X is volatile, and they combine with other... 

Halide ion Y" in the form of soluble tetraalkylammonium salts can in some cases displace halide ion X forming a mixed-halogen adduct. However, the method has met with variable success. It is successful with tetrahaloborate ions (80) and with Me3N BI3 (9). A similar reaction with insoluble silver halides or pseudohalides has also given mixed adducts (43). 

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