Metal hydrazines

Inorganic Hydrazine Derivatives Synthesis, Properties and Applications, First Edition. Edited by K. C. Patil and Tanu Mimani Rattan. 

Common synthetic methods practiced for the preparation of metal hydrazines, and some single-crystal structures, are discussed briefly in Chapter 1. A direct method of synthesis of metal hydrazines has been developed that involves adding metal powders to hydrazine salts (preparation of salts discussed in Chapter 2). Details of the synthesis of several simple and mixed metal hydrazines by this and other methods, along with their spectral characterization and thermal reactivity, are now described. 

The synthesis of metal hydrazine complexes with thiocyanate or isothiocyanate as anions can be carried out by the following methods [8]. In the first case, stoichiometric quantities of metal(II) salts like chlorides or sulfates of Mn, Fe, Co, Ni, Zn, and Cd in an alcohol-water mixture (1 1 by volume) are added to hydrazinium thiocyanate. The latter is metathet-ically formed by the reaction of NH4SCN -I- N2H4 H2O (1 1 mole ratio) (Chapter 2)  

Alternatively, the metal salt is mixed with ammonium thiocyanate and hydrazine hydrate in 1 2 2 mole ratio  

In another method, metal powders free from an oxide film are added directly to a solution of N2H5SCN in hydrazine hydrate. Owing to the high acidic nature of hydrazinium thiocyanate formed in situ, the metal powders dissolve instantaneously with the liberation of hydrogen gas, forming metal isothiocyanate hydrazines  

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Arsenic trioxide arsenic detection, metals Hydrazine sulfate... 

Several nanocrystalhne metal oxides have been prepared by the combustion method and the topic has been reviewed by Patil et al. [5]. Combustion of metal hydrazine carboxylates, [e.g. MCjO (N H )J is generally anployed to obtain the nanoparticles of oxides such as y-Fefiy ZnO and NiO. Mixed-metal oxides like cobaltites (MCo O ), ferrites (MFe,0 ), manganites (MMn O ) and titanates (MTiOj) are prepared by the combustion of mixed-metal carboxylate hydrazinates in the temperature range of 165-345 °C [6,7]. Solution combustion synthesis has been used to prepare nanocrystalline oxides such as Al Oj, CeO, ZrO, TiO, ... 

Table 13.8 Form and color of metallic hydrazine nitrates [16]...

With bivalent metals, hydrazine nitrate forms coordination compounds that may be represented by the general formula Me[(N2H4)2 3l(N03)2 [6]. The two most often mentioned substances are nickel hydrazine nitrate (NHN) and cobalt hydrazine nitrate (CoNH). 

The description of crystal type and color of several metallic hydrazine nitrates are summarized in Table 13.8. The density of NHN is 2.07 g cm . Nickel and cobalt hydrazine nitrate are practically insoluble in common organic solvents (e.g., ethanol, acetone) and sparingly soluble in water (0.47 g 1 at 30 °C, 2.31 g 1 at 70 °C). NHN bums upon the action of 96 % sulfiuic acid, but weak acid makes it decompose more gently CoHN explodes in contact with concentrated sulfuric acid. NHN mildly reacts with a 10 % solution of sodium hydroxide and this can be used for producing a chemical decomposition. NHN is stable on exposure to sunlight and it hardly reacts at aU with common metals. Cobalt hydrazine nitrate is unstable and decomposes slowly, even in the presence of traces of moisture, changing in color from brown to greenish [16, 17]. 

Impact sensitivity and ignition temperature for several metallic hydrazine nitrates are summarized in Table 13.9. 

Table 13.9 Metallic hydrazine nitrates ignition temperatures and sensitivity to impact and friction...

Metallic hydrazine nitrates is prepared by the reaction of the relevant nitrate with hydrazine in water or alcohol [16, 21], The product is isolated from the reaction mixture as a precipitate [6]. The preparation of NHN according to the procedure of Zhu [21] gives 95 % yield and leads to fine powder shown in Fig 13.2. 

The hydrazine was chosen as appropriate reducing agent because it can be used at low temperature and it decomposes to NH3 and/or N2 after reduction takes place. The reduction with hydrazine depends on several parameters such as the nature of the metal, hydrazine concentration, pH, time of reduction and reduction temperature. In case of the noble metals such as palladium, this reaction occurred very easily at low temperature. In our case the hydrazine to palladium molar ratio was 100 (particle size is independent on hydrazine eoncentration). Under this condition the particle size should be mainly governed by the natme of solvent and surfactant. Moreover, in our study, the water to surfactant molar ratio was 6 which let us to suppose the presence of bounded and trapped water only. This is expected to result in very small size of palladium nanoparticles [4]. 

Molecule Solvated Hydrazine N2H4 Metal hydrazine complexes M(A)(N2H4)y M — meml A = anion (inoiganic/oiganic) y s 1 ... 

Various methods that have been used for the preparation of metal hydrazine complexes are listed below ... 

Metal hydrazine carboxylates [M(N2H3COO)2-(N2H4)2] are prepared from aqueous solutions of metals salts with hydrazine carboxylic acid in hydrazine hydrate ... 

The redox property of hydrazine stabilizes the lowest oxidation state of the metal in all its metal hydrazine complexes. It is not possible to prepare platinum or palladium hydrazines as they are reduced to metals [24]. 

In all these complexes the N—N bond length is found to range between 1.45 and 1.48 A, which is the same as in hydrazine or complexes containing monodentate hydrazine. Hydrazine is also present as a mono-dentate ligand in metal hydrazine carboxylate hydrazine complexes [25]. 

Table 1.5 Crystal data and N—N bond distances in metal hydrazine complexes.

Metal hydrazine carboxylate complexes can be prepared by the reaction of the respective metal ions with hydrazine hydrate, kept open to atmosphere or saturated with CO2 gas. Carbon dioxide is absorbed by hydrazine, forming the hydrazine carboxylate anion, which coordinates with the metal ions to give crystalline compounds. Chemical equations for the formation of various complexes are ... 

Table 1.6 Crystal structure data of metal hydrazine carboxylates.

Inorganic derivatives of hydrazine Hydrazine salts and metal hydrazine complexes of perchlorate, nitrate, azide, hydrazinium nitroformate, or azide Hydrazinium azide... 

Metal hydrazine carboxylates Organic derivatives of hydrazine Monomethyl hydrazine (MMH) and unsymmetrical dimethyl hydrazine (UDMH)... 

Gajapathy, D. (1983) Studies on metal-hydrazine system. Ph.D Thesis, Indian Institute of Science, Bangalore. 

Patil, K.C. and Seker, M.M.A. (1994) Synthesis, structure and reactivity of metal hydrazine carboxylates combustible precursors to fine particle oxide materials. International Journal of Self-Propagating High-Temperature Synthesis, 3, 181-196. 

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