Normal Azides

The moisture-sensitive compounds are made from sodium azide and the respective chlorides at moderate or low temperatures and are obtained as oily liquids of extreme sensitivity. Examples are, triphosphonitrile azide (a), cyanogen azide (b), and chromyl azide (c). Saltlike compounds with composite cations, such as ammonium and hydrazine azides, are not considered hetero azides, but normal azides. 

Azido complexes are coordination compounds with azide ions as inner-sphere ligands and may be cationic, such as azidopentaaquocobalt(III) (d) or anionic, such as hexaazidocuprate (e) or neutral, such as dipyridine diazidozinc (0- There are mixed-ligand complexes, such as (d) and (f), and all-azido 

These compounds, combining metal-to-carbon and metal-to-azide bonds, are abundant in the right-hand half of the periodic table (groups VIII to VIA). Most of them, like triethyllead(rV) azide (g), are covalent, while some, like trimethyl-arsenic(V) azide (h), form ions. Most of these compounds do not explode, indi- 

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To satisfy the bond-stabilization concept, it appears essential to reclassify the inorganic azides. Hence, five classes are identified here and are listed in Figure 1 as normal azides, mixed azides, hetero azides, azido complexes, and metalorganic azides. 

This class is composed of simple inorganic compounds in which all available valencies are bound to azide groups hence, the ionicity of the element-to-azide bonds alone determines chemical reactivity. Accordingly, normal azides of the more electropositive metals are saltlike and may be made in aqueous solution and the rest in nonaqueous media some of the covalent normal azides require handling in closed systems. The explosive character may in this class likewise be derived from formal ionicities in fact, the normal azides are the only class to which the traditional concept of stable ionic and unstable covalent azides still applies. 

Normal azides are not known in group IIIB. Curtius and Darapsky [135] attempted to make them by dissolving, for example, lanthanum hydroxide in hydrazoic acid. The solution was assumed to contain the normal azide but only basic products were precipitated upon evaporation or by adding alcohol. The precipitate was insoluble in water, had the approximate composition La(OH)(N3)2 I.5H2O, and deflagrated upon heating. The same results were found with yttrium, cerium, dysprosium, thorium, and uranium azides. Based on the infrared spectra, Rosenwasser and Bryant [136] suggested two types of basic rare earth azides. The lanthanum type (a) was found for lanthanum, neodymium. 

Chromium(III) forms the normal azide, a number of basic azides and azido complexes, and a chromium(VI) hetero azide. All these compounds reflect the properties of their respective classes (see p. 21). 

Of the five oxidation states of manganese, only Mn(II) forms azides. The normal azide, Mn(N3)2, consists of white, sandy crystals which are chemically and explosively not very stable thus, exposure to the atmosphere causes a brown discoloration (oxidation to Mn02), and the compound explodes above 218°C and is sensitive to impact and friction [54,115,143]. The azide is not easy to make, as dissolving manganous carbonate in hydrazoic acid yields basic products [62,135]. Reaction of the dry carbonate with ethereal hydrazoic acid is impractically slow, but the latter yields Mn(N3)2 when shaken with basic manganese azide for three days [54]. 

Normal azide Mixed azide Azido complex Metal- organic azide... 

The normal azide, Ni(N3)2, is a green, hygroscopic solid which dissolves readily in water upon standing or heating, hydrolyzed products are precipitated [135]. The compound is extremely sensitive to thermal or mechanical shock [54]. 

Not much is known about the normal azide Pd(N3)2 except that it is a brown, water-insoluble solid which is very sensitive to heat, friction, and impact [139,158]. It is precipitated when solutions of palladium salts and azide are combined, e.g., 0.1 M sodium azide and 0.01 M palladium perchlorate are mixed in molar ratios, but the precipitate cannot be dried without exploding [166]. This azide is occasionally obtained as an undesired intermediate to the complex paDadium azides. 

The normal azides of this group are powerful explosives, displaying various degrees of sensitivity, and two of them are of prime interest in explosives technology silver azide as an initiator for explosive devices, and copper azide as... 

Ionic character of the azide bond (%) Normal azide Mixed azide Hetero azide Azido complex Metal- organic azide... 

All copper azides explode, but the sensitivities vary widely. It is extremely high in the normal azides, Cu(N3) and Cu(N3)2. At the other end of the scale are almost insensitive azido complexes of large organic cations. In general, a copper azide is more sensitive than the respective lead azide. 

Basic copper(II) azides occur as four distinct phases (Table XI), which have been described as water-insoluble, explosive solids. They are less sensitive to thermal and mechanical shock than the normal azide the Cu(N3)2 Cu(OH)2 phase explodes at 245°C (normal azide, 202°C) and deflagrates on impact. In principle these compounds are formed by partial hydrolysis of Cu(N3)2, or by partial azidation of Cu(OH)2 ... 

The normal azides of Au(I) and Au(III) have never been described, but a complex azidoaurate has been known since 1898, when Curtius and Rissom [62] reported on Doppelsalze von Platin- und Goldaziden (double salts of platinum and gold azides). The complexes were made in aqueous media from potassium azide and, e.g., H2PtCl6, according to... 

The normal azide, Zn(N3)2, is a white, sandy powder which is hygroscopic and has a strong tendency to decompose hydrolytically. Thus, the odor of HN3 appears immediately when the solid is exposed to atmospheric moisture, and in time aqueous solutions separate voluminous precipitations of basic products. These basic salts are inherently poorly defined, and the basic zinc azides and zinc hydroxyazides of the literature may have analyses anywhere between Zn(N3)2 and Zn(OH)2. Nevertheless, two discrete phases of the composition (OH)Zn(N3) and Zn3(OH)s Zn2(N3) were determined by X-ray analysis, but the method of preparing them was not given [160]. Recently, the existence of a dihydrate, Zn(N3)2 2H2O, has been suggested, with a dehydration point at 27.5°C[211]. 

The azides of group fVA display properties which are, for the most part, symptomatic of covalent element-to-azide bonds. Evidence of ionic influence appears late in the group and remains small, for example in the ability to form an azido complex of Sn(IV). Even the azides of lead, the most electropositive IVA metal, are predominantly covalent, although the ionic bonding component is sufficiently strong to form the only divalent normal azide of the group. 

Lead forms various azides in its tetravalent state like the other IVA elements, but is the only member of the group to also form a normal azide in its lower (Pb ) oxidation state. 

Of all known normal azides including HN3, fluorine azide appears to be the most sensitive. The greenish-yellow gas was obtained in a nitrogen or argon environment at low temperatures. Slow mixing of diluted (1 200) fluorine and HN3 yielded the azide, apparently according to [334] ... 

In the previous paper (34), there were speculations about the configuration of heme a. Two compounds of heme are observed in half-reduced cytochrome c oxidase. One is a normal hydroxide, and, in the case when azide is added, there is a normal azide. This tells us that under these conditions, the heme is behaving as a normal isolated heme, and does not have a peculiar configuration in cytochrome c oxidase under these conditions. 

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