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1 CHAPTER 1 INTRODUCTION 1.1 HYDRAZINE Hydrazine is the simplest diamine in its class of compounds and may be thought of as derived from ammonia by replacement of a hydrogen atom by the – NH2 group. The hydrated hydrazine, N2H4.H2O was first prepared by Curtius in 1887. The anhydrous hydrazine as a water free base was prepared by De Bruyn for the first time. Preparation of hydrazine by the oxidation of NH3 with hypochlorite – a process that became the chief commercial method of manufacture was first demonstrated by Raschig. For many years hydrazine was considered as a special chemical available only in aqueous solution and in the formation of few salts. It remained as a laboratory curiosity for over 50 years. During the Second World War, Germany discovered the interesting property of hydrazine as a rocket fuel. Now it is one of the most powerful liquid fuels among current rocket propellants. However, the chemical uses of hydrazine now far surpass its use as a fuel. The bibliographic works on hydrazine (Bottomley 1970, Schmidt 1984) are indispensable bibles for hydrazine chemists. The field of hydrazine chemistry and its applications are over widening. 1.1.1 Applications Anhydrous hydrazine (m.p. 2 °C, b.p.114 °C), a fuming colourless liquid, is surprisingly stable in view of its endothermic nature(∆Hf = 50.43KJ /mol) and its simple methyl and dimethyl derivatives have endothermic heats of formation and 2 high heats of combustion. They have nitrogen in -2 valence state. Nitrogen's natural tendency, however, is towards zero valency (N ≡ N), which gives off nearly six times as much as energy as the N-N bond. Thus tremendous amount of energy is released not only during decomposition of N2H4 to N2 but also at the time of the mixing with the oxidizer. Hence they are used as fuels in rocket and spacecraft powered engines. As a strong reducing agent, hydrazine is used for corrosion control in boilers and hot water heating systems, for metal plating, and for reducing noble metal catalysts and unsaturated bonds in organic compounds. It is also an oxidizing agent under suitable conditions with two active nucleophilic nitrogens and four replaceable hydrogens. It is the starting material for many derivatives; among which, foaming agents for plastics, antioxidants, polymers, polymer cross linking and chain extending agents, as well as biologically active pesticides, herbicides, plant growth regulators and pharmaceuticals are important. As it is a good complexing ligand, numerous complexes have been studied (Bottomley 1970 and Schmidt 1984). Many heterocyclics are based on hydrazine, with rings containing from 1 to 5 nitrogen atoms as well as other hetero atoms. The many advantageous properties of hydrazine are exploited in the field of photographic chemicals and dyes. New uses for hydrazine derivatives are discovered daily. 1.1.2 Basicity and Salt Forming Ability As an Arrhenius base, hydrazine is a weaker base than ammonia because the more electronegative group NH2 has the - I effect on the lone pair of electron of the neighbouring nitrogen, making it less basic for protonation. NH3 + H2O → NH4+ + OH - Kb =1.8 X 10-5 (1.1) N2H4 + H2O → N2H5 + + OH - Kb = 8.5 X 10-7 (1.2) 3 N2H5+ + H2O → N2H62+ + OH - Kb = 8.9 X 10-16 (1.3) In principle, it can form two series of salts with monobasic acids, one having the hydrazinium (+1) cation, N2H5+ and the other, hydrazinium(+2) cation, N2H62+. The basic ionization constants of hydrazine in water suggest that N2H62+ exists only in the solid state or in conc. acid solutions. The salts containing this cation are extensively hydrolyzed in water to give highly acidic solutions containing the N2H5+ ion. N2H62+ + H2O → N2H5+ + H3O+ (1.4) The divalent cation seems to violate Pauling’s adjacent charge rule, H3N+- NH3+, but is likely that this is in equilibrium with other tautomeric forms, e.g. H3N+- NH2H+.The N2H5+ salts have been prepared with carboxylic acids and numerous examples of them have been reported (Schmidt 1984), whereas the salts of N2H62+ are limited (Starosta and Leciejewicz 2007, Starosta and Leciejewicz 2008). 1.2 TYPES OF HYDRAZINE SALTS The hydrazinium salts are inorganic derivatives, well-crystallized and colorless compounds, comparable to the corresponding ammonium salts. The reducing property and the lack of thermal stability of hydrazinium salts differentiate them from ammonium salts. Hydrazine forms not only mono- and di acid salts of the types, N2H4·HA, N2H4·2HA where HA represents a simple mono-basic acid, but also compounds of the types 2N2H4·H2B and N2H4·H2B where H2B represents a dibasic acid. The best known of these are N2H4·HA or 2N2H4·H2B [N2H5A or (N2H5)2B] and N2H4·2HA or 4 N2H4·H2B [N2H6A2 or N2H6B] and not N2H4·2H2B. The N2H5+ and N2H62+ salts are generally referred to as hydrazinium(+1) and hydrazinium(+2) salts respectively. Even though N2H62+ salts are generally formed with strong acids, double salts of this cation with ammonium ion are also formed. For example, (NH4)2N2H6(ClO4)4 and (NH4)2N2H6(SO4)2 (Frech et al 1993) salts have been prepared and characterized. Recently redetermination of hydrazinium (+2) dichloride (N2H62+.2Cl-) has been reported (Kruszynski and Trzesowska 2007). In many cases the preparation of hydrazinium salts is very easy, but in other cases, such as in the preparation of hydrazinium nitrates or perchlorates, special precautions are necessary to prevent unexpected explosions. It is interesting to note that a few hydrazine salts form hydrates: e.g. N2H5ClO4.0.5H2O, N2H6X2.2H2O, X = ClO4-, Br- and I-. It has been shown by IR, thermal and conductivity measurements that water in these compounds is partially present as oxonium ion H3O+ and involved in hydrogen bonding with N2H4 (Patil et al 1983), (N2H5)2SO3.H2O (Patil et al 1980). 1.2.1 Methods of Preparation of Simple Hydrazinium Salts 1.2.1.1 Acid -Base Neutralization Method In this method, the base is directly neutralized by the addition of the corresponding acids in the aqueous medium. The pH of the solution is an important factor to get the type of salt desired. The reactions are represented as given below: → N2H5A + H2O (1.5) N2H4. H2O + 2HA → N2H6A2 + H2O (1.6) N2H4. H2O + H2B → N2H6B + H2O (1.7) N2H4.H2O + HA 5 where HA is a monobasic acid, e.g., HCl, CH3COOH, HNO3 etc. and H2B is a dibasic acid, e.g. H2SO4, H2C2O4 etc.Acids like H2SO4 (Hudson et al 1967) and HF (Patil et al 1979) react with N2H4.H2O to form exclusively N2H62+ salts because of their strong acidic nature and the low solubility of the resulting salts. 1.2.1.2 Double Decomposition Method Hydrazinium sulphate (N2H5)2SO4, reacts with the corresponding barium salts (Jones 1975) in the aqueous medium to form the salts. For example, (N2H5)2SO4 + Ba(NO3)2 → BaSO4 + 2 N2H5NO3 1.2.1.3 (1.8) Decomposition Method of Ammonium Salts The reaction of stoichiometric quantities of N2H4.H2O and the simple ammonium salts (Soundararajan 1979) produces the hydrazinium salts with the liberation of NH3. NH4X + N2H4.H2O → N2H5X + NH3+ H2O (1.9) where x = halides, NO3-, N3-, CH3COO -, H2PO4 -, HF2-, HSO4- etc. (NH4)2Y + 2N2H4.H2O → (N2H5)2Y + 2NH3 + 2H2O (1.10) where Y = SO42-, C2O42-, HPO42-, S2O32- etc. This method is a heterogeneous reaction. The salts N2H5HF2 (Patil et al 1979) and N2H5HSO4 (Vittal 1981) which could not be prepared by other methods, can be prepared by this method. The hydrazinium (+2) salts containing one molecule of a simple binary acid are stable in solution. The diacid salts, however, exist in the solid state and undergo immediate hydrolysis when dissolved in water (Nesamani 1982). The monoacid salts N2H4.HA [N2H5 A] are usually more soluble in water than the diacid 6 salts N2H4·2HA (N2H6 A2). Again N2H5+ salts are mostly hygroscopic and even some of them are in liquid state (Patil et al 1980), while N2H62+ salts are not so, with an exception of N2H6(ClO4)2.2H2O which is highly hygroscopic. 1.2.2 Salts of Hydrazine with Different Acids 1.2.2.1 With Inorganic acids Hydrazine hydrate reacts with halogen acids to give salts of the type N2H5X and N2H6X2 under different reaction conditions (Patil et al 1979, Patil et al 1978), where X = Cl-, Br-, I- or F-. When pure hydrazine reacts with nitric acid it forms hydrazinium (+) nitrate and its crystal structure is reported (Grigoriev et al 2005). Hydrazine and nitrous acid undergo mutual destructive reaction. In neutral solution it is possible to obtain hydrazinium(+1) nitrite as colorless to yellowish hygroscopic solid. Hydrazinium (+1) hydrogensulphate, has been prepared (Patil and Vittal 1982) for the first time by the reaction of solid ammonium hydrogen sulphate with hydrazine hydrate. 2N2H6SO4 + BaCO3 → BaSO4 + (N2H5)2SO4 + H2O + CO2 (1.11) Hydrazinium (+2) dithionate, N2H6S2O6 can be prepared from hydrazinium (+2) sulphate and barium dithionate. Hydrazinium (+2) sulphamate is prepared in a similar fashion from N2H6SO4 and Ba(SO3NH2)2. When SO2 gas is passed through a 1:1 aqueous solution of hydrazine, N2H5HSO3 is formed in less concentrated solution, whereas (N2H5)2S2O5 is formed in more concentrated solution, no hydrazinium sulphate formation is observed. Earlier studies have reported the formation of dihydrazinium hydrazodisulphite, (HNSOON2H5)2 by the same reaction. Bubbling SO2 into an alcoholic solution of 7 hydrazine hydrate, precipitates (N2H5)2SO3, which can also be prepared (Patil et al 1980) by the heterogeneous reaction between solid ammonium sulphite and hydrazine hydrate. The reaction of hydrazine with a mixture of SO2 and CO2 results in dual substitution on both nitrogen atoms to give a mixed sulphinate carbazate N2H5OOSNHNHCOON2H5. On passing SO3 into an excess anhydrous hydrazine, it gives the hydrazinium salt of hydrazinosulphuric acid, N2H3SO3N2H5. The hydrazinium thiocyanate has been prepared from solid ammonium thiocyanate and hydrazine hydrate (Patil et al 1980). The latter salt also forms 1:1 adduct with phosphoric acid: N2H5H2PO4 .H3PO4. The salts N2H5H2PO4 and (N2H5)2HPO4 have been prepared by the reaction between the corresponding ammonium phosphate and hydrazine hydrate and characterized (Patil et al 1978) by chemical analysis and IR spectra(νN-N = 980 cm -1). NH4 H2PO4 (S) + N2H4.H2O → N2H5H2PO4 (S) + H2O + NH3 (1.12) (NH4)2HPO4 (S) + 2N2H4.H2O → (N2H5)2HPO4 (S) + 2H2O + 2NH3 (1.13) The crystal structures of N2H5H2PO4 and N2H6(H2PO4)2 have also been studied (Liminga 1965 and Liminga 1966). Trihydrazinium (+1) dihydrogentriphosphate, (N2H5)3H2P3O10 and tetra hydrazinium (+1) tetrametaphosphate, (N2H5)4P4O12 were prepared as anhydrous salts, whereas tetrahydrazinium(+1) pyrophosphate, (N2H5)4P2O7.H2O and octa meta phosphate, (N2H5)8P8O24 .H2O were obtained as hydrates. 8 1.2.2.2 With carboxylic acids The hydrazinium salts of a number of aliphatic mono and di carboxylic acids, and aromatic mono, di, tri and tetra carboxylic acids have been reported. Hydrazinium (+1) formate (hydrazinium monoformate), though reported (Schmidt 1984) to have been prepared from formic acid and hydrazine hydrate, has not been well characterized. The preparation of hydrazinium(+1) acetate has been reported by the decomposition of ammonium acetate by hydrazine hydrate (Patil et al 1980). The dihydrazinium(+1) oxalate, (N2H5)2C2O4, has been repeatedly studied, because it is a well crystallized solid and also forms double salts with other cations. The metathetical reaction of ammonium oxalate monohydrate with excess of N2H4.H2O gives (COON2H5)2.N2H4, which begins to lose solvated hydrazine at 90 °C and then melts at 153 °C (Patil et al 1979 and Patil et al 1978). The hydrazinium(+1) oxalate can be obtained by treating hydrazinium(+2) oxalate in aqueous solution with N2H4.H2O until the solution becomes permanently alkaline. The N2H5HC2O4 has been prepared by mixing hot aqueous solutions, whereas (N2H5)2C2O4 has been prepared in cold condition. Efforts to crystallize the latter from hot solution always resulted in the former only. Numerous salts of hydrazine with several organic acids are available in the literature. Some of the common salts are N2H5.C7H4NO3S (Banerjee et al 2006), hydrazinium propionate, butyrate(Schmidt 1984). Moreover, hydrazinium salts of a series of dicarboxylic acids like hydrazinium hydrogenmalonate, hydrogenglutarate, hydrogenadipate and dihydrazinium succinate (Sivasankar 1994), higher homologous dicarboxylic acids viz. pimelic, suberic, azelaic, alpha keto glutaric and iminodiacetic, malic, aspartic and glutamic acids (Yasodhai and Govindarajan 1999), oxydiacetic acid (Yasodhai and Govindarajan 2000), heteroaromatic acids 9 like pyridine dicarboxylic acids (Saravanan and Govindarajan 2003) and pyrazine carboxylic acids (Premkumar et al 2003) have been prepared by the acid-base neutralisation method and characterized. Hydrazine also forms salts with aromatic carboxylic acids like benzoic, salicylic, phthalic acids (Kuppusamy 1995), trimesic, trimellitic, hemimellitic and pyromellitic acids (Vairam and Govindarajan 2004), naphthoic, hydroxy naphthoic and naphthoxy acetic acids (Arunadevi 2009). Simple hydrazinium salts have numerous applications (Schmidt 1984), such as a source of anhydrous hydrazine, additives in propellants, drugs, to treat cancer and Hodgkin’s disease, explosives(Schimidt 1984) and as ligands to prepare metal hydrazine/hydrazinium complexes(Govindarjan et al 1986, Govindarajan et al 1986a and Yasodhai et al 1999) . A few of them are also used as flame retardants (Patil et al 1980 and Patil et al 1981) and proton conductors (Chandra and Singh 1983). 1.3 THERMAL PROPERTIES OF HYDRAZINE AND ITS SIMPLE SALTS Heating of hydrazine salts, in most cases causes decomposition. A very few of them are stable at their melting points. The diacid salts on heating decompose to yield the monoacid salts as intermediates. N2H4.2HA → N2H4.HA + HA (1.14) The hydrazinium salts of the type N2H5X [X = Cl-, Br-, I-, 0.5SO42-, H2PO4-] decompose exothermally in air to the corresponding ammonium salts with the evolution of ammonia and nitrogen (Patil et al 1979 and Jasim 1988). Some of the hydrazinium salts like N2H5N3 (Patil et al 1979), N2H5HF2 (Patil et al 1979) and N2H5F (Soundararajan 1979) do not decompose exothermally, but volatilize under the conditions employed. The simultaneous TG, DTA and EGA thermolysis of hydrazinium sulphate has also been studied (Jasim 1988). The hydrazine salts such 10 as hydrazinium perchlorate and nitrate are used as high energy oxidisers in propellants. Hence, thermal decomposition of these compounds has been investigated in detail (Pai Verneker et al 1976, Breisacher et al 1972 and Patil et al 1980). Thermal studies on hydrazinium sulphite hydrate (Patil et al 1980) shows that it melts before decomposition. In the same report, an interesting and quantitative conversion of hydrazinium thiocyanate to thiosemicarbazide has been discussed. The thermal decomposition of hydrazinium carboxylates is more interesting. The hydrazinium formate hemihydrate (Sivasankar and Govindarajan 1995) melts before undergoing endothermic decomposition to gaseous products. The hydrazinium acetate also follows the same pattern of thermal decomposition as already reported (Patil et al 1980). The thermal decomposition of hydrazinium hydrogen oxalate and dihydrazinium oxalate has been investigated in detail (Udupa 1982, Gajapathy et al 1983). An interesting behaviour in their thermal properties is that dihydrazinium salt is converted to monohydrazinium salt after melting and losing one N2H4 molecule. The thermal decomposition of hydrazinium dicarboxylates of malonic, succinic, glutaric, adipic acid (Yasodhai and Govindarajan 1999) and phthalic acids has been studied by TG-DTA method. All of them, except terephthalate and isophthalates, decompose to gaseous products endothermally (Sivasankar 1994). Terephthalate and isophthalate salts (Kuppusamy et al 1995) undergo exothermic and endothermic decompositions. Hemimellitate, trimellitate, trimesate and pyromellitate salts undergo strong exothermic decomposition with the formation of carbon residue as the final product (Vairam and Govindarajan 2004). 11 1.4 METAL HYDRAZINE COMPLEXES The hydrazine does not frequently act as a reducing agent in reactions with transition metals but acts as a ligand to form complexes. This broad area of hydrazine complexes has been reviewed earlier (Bottomley 1970, Dilworth 1976). 1.4.1 Hydrazine as a Ligand Hydrazine, like other polybasic ligands, offers the possibility of several different types of coordination behavior towards metal ions. It can, of course, function as a monodentate ligand but may also serve as either a bridging or chelating bidentate ligand. Although numerous examples of both monodentate and bridging hydrazine have been demonstrated crystallographically, no verified examples (with the possible exception of (i-pro)4MN2H4, M = Ti or Zr) of chelatively bound hydrazine have been reported. Monoprotonated hydrazine, hydrazinium cation (N2H5+) still retains a basic site and is capable of coordination. It is potentially a monodentate ligand and complexes containing it are known. The donor abilities of hydrazine from complexometric titration (Bisacchi and Goldwhite 1970) are shown in the order: N2H4 > CH3NHNH2 > C2H5NHNH2 > (CH3)2NNH2 (1.15) A number of complexes with substituted hydrazines have been reviewed by Heaton et al 1996. 12 1.4.2 Synthesis of Metal Hydrazine Complexes 1.4.2.1 Reactions of Hydrazine and its Salts with Metal The high dielectric constant of anhydrous hydrazine suggests that it would be a moderate solvent for many ionic compounds. It is not altogether unexpected to find that hydrazine salts when dissolved in hydrazine or hydrazine hydrate behave as acids. Thus, metals like Mg, Fe, Co, Ni, Zn, or Cd dissolved in a solution containing hydrazine hydrate and hydrazinium or ammonium salts liberate hydrogen (Patil et al 1982). M + 2N2H5X → M(N2H4)2X2+ H2 (1.16) where X = 0.5 SO42-, 0.5 C2O42-, N3-, ClO4- etc. Some mixed metal oxalate derivatives such as MFe2(C2O4)3(N2H4)x (M = Mg, Mn, Co, Ni, or Zn: x = 5 and 6 ) and MgFe2(N2O2)3(N2H4)5 (Gajapathy 1982) have been synthesized using the above procedure. The complex (N2H5)2Mg(SO4)2 has been prepared by the reaction of magnesium powder and ammonium sulphate in the presence of hydrazine hydrate (Patil et al 1981). 1.4.2.2 Reactions of Hydrazine with Metal Salts The insoluble complexes M(N2H4)2X2, (M = Mn, Co, Ni, Zn or Cd and X = Cl-, Br-, I-, 0.5SO42-, NCS-, HCOO-, CH3COO-, 0.5C2O42-, H2NCH2COO-, HOCH2COO- etc.) (Srivastava et al 1980, House and Vandenbrook 1989, House and Vandenbrook 1990, Anagnostopoulos et al 1979, Ravindranathan and Patil 1983 and 13 Mahesh and Patil 1986) are the usual products of reaction between hydrazine hydrate and first row transition metal salts. The tris-hydrazine complexes M(N2H4)3X2(X= 0.5 SO42-, 0.5SO3-, 0.5S2O3-, NO3- etc.) (Anagnostopoulos and Nicholls 1976 and Athavale and Padmamabha Iyer 1967) have been prepared by the reaction between the transition metal salts and hydrazine hydrate. The tris-hydrazine metal glycinates and glycolates M(XCH2COO)2(N2H4)3,(X = NH2- or OH- and M = Mn, Co, Ni, Zn or Cd) have been prepared (Sivasankar and Govindarajan 1994) by mixing the metal nitrate hydrates and a mixture of the acid and excess hydrazine hydrate. The copper (II) complex, however, is particularly difficult to isolate from aqueous solution because of its ease of reduction. Synthesis of bis(hydrazine) complexes, [Fe(RNHNH2)2{PPh(OEt)2}4](Albertin et al 2001) was achieved by reacting bis(nitrile)complex [Fe(CH3CN)2{PPh(OEt)2}4](BPh4)2 with an excess of hydrazine. Also, with the triethyl phosphate complex [Fe(CH3CN)2{P(OEt)3}4](BPh4)2 as a precursor, the reaction with NH2NH2 gave the new nitrile-hydrazine [Fe(NH2NH2)(CH3CN)2{P(OEt)3}3](BPh 4)2 derivative. 1.4.2.3 Reactions of Hydrazinium Salts with Metal Salts The hydrazinum salts such as N2H6BeF4, N2H6F2, N2H5F, N2H4.2HF, N2H5Cl, N2H4.HCl, N2H4.2HCl, N2H5Br, N2H6SO4, (N2H5)2SO4, (N2H5)2C2O4, (N2H5)2H2EDTA, N2H3COON2H5, N2H5NCS etc., react directly with transition metal salts to form normally hydrazinium(+1) metal complexes (Tedenac et al 1971, Satpathy and Sahoo 1970, Bukovec and Golic 1976, Kumar et al 1991, Cheng et al 1977, Reiff et al 1977, Witteveen and Reedijk 1973, Witteveen and Reedijk 1974, Nieuwpoort and Reedijk 1973, Govindarajan et al 1986, Gajapathy et al 1983, Saravanan et al 1994) or hydrazine adducts of the corresponding metal salts 14 (Sivasankar and Govindarajan 1994, Patil et al 1983 and Sivasankar and Govindarajan 1995). The hydrazinium (+2) metal complexes have also been isolated and studied (Glavic et al 1975, Slivnik et al 1968, Frlec et al 1980). The hydrazinium (+1) lanthanide metal sulphate complexes have been prepared by the reaction between the lanthanide salts and N2H6SO4 and studied systematically (Bukovec and Miliev 1987 and Govindarajan et al 1986). 1.4.2.4 Reactions of Hydrazine Hydrate and the Acid Mixture with Metal Salts Instead of hydrazinium salts, the mixture of hydrazine hydrate and the acid of the corresponding anion can be added to the metal salt solution which precipitates the complexes containing bidentate bridging hydrazine, N2H5+ or N2H62+. This method is suitable when the particular hydrazinium salts cannot be prepared in the solid form. A report describes the preparation of MX(N2H4)2 (M = Co, Ni, Zn or Cd ; X = malonate or succinate) complexes by adding a mixture of hydrazine hydrate and the acids to the metal nitrate hydrates (Sivasankar and Govindarajan 1994). The complexes of propionate, M(CH3CH2COO)2(N2H4)2 (M = Mn, Co, Ni, Zn or Cd) and M1/3Co2/3(CH3CH2COO)2(N2H4)2 (M = Mg, Mn, Ni, Zn or Cd) have been prepared by this method. The N2H62+ containing complexes like N2H6SbF5 (Ballard et al 1976), N2H6CrF5.H2O (Bukovec 1974) have been prepared by adding the mixture of 40 % HF and N2H4.H2O to CrF3 in the aqueous medium. 15 1.4.2.5 Reactions of Hydrazinium Salt with Metal Salts in the Presence of Excess Acid This method is suitable to prepare the complexes in acidic pH, so that N2H5+ or N2H62+ cation containing complexes can be obtained. For example, N2H5CuCl3, (N2H5)2CuCl4.2H2O and (N2H5)2Cu3Cl6 complexes (Brown et al 1979) have been prepared by adding 3M HCl and N2H6Cl2 mixture to the aqueous solution of CuCl2.2H2O under different conditions. Under this condition of acidic pH the reduction of Cu(II) is also prevented. The complexes of the type (N2H5)Ln(SO4)2.H2O (Ln = La, Ce, Pr, Nd, Sm) have been prepared (Govindarajan et al 1986) by this technique. The N2H6FeF5 has been synthesized from metallic Fe, HF and aqueous N2H6F2 (Hanzel et al 1977 and Hanzel et al 1974). A number of N2H62+ containing metal complexes with fluoride anion have been prepared by this method in which metal fluorides react with a mixture of HF and N2H6F2 in the aqueous medium (Slivnik 1976, Frlec et al 1981 and Chakravorti and Pandit 1974). The hydrazinium formato and acetato complexes, (N2H5)2M(XCOO)4, (X = H or CH3; M= Co, Ni or Zn) have been prepared (Sivasankar 1994 and Sivasankar and Govindarajan 1995) by the reaction of metal nitrate hydrates with the corresponding hydrazinium salts and acid mixture. 1.4.2.6 Reactions of Hydrazine Carboxylate Complexes with Acids Whenever it is not possible to prepare hydrazinium metal complexes with particular anion, the same can be prepared conveniently by decomposing hydrazinium metal hydrazine carboxylates with dilute acids of the corresponding anion. For example, (N2H5)2M(NCS)4.2H2O (M = Co or Ni) complexes have been prepared (Kumar et al 1991) by adding freshly prepared solid 16 N2H5M(N2H3COO)3.H2O to dilute thiocyanic acid in small portions while maintaining the reaction temperature around 0°C. The (N2H5)2MnF4, (N2H5)2MCl4.2H2O (M = Co or Ni) (Kumar et al 1991) and (N2H5)UO2(CH3COO)3 complexes have been prepared by the same procedure. In spite of a number of methods described for the preparation of the complexes, it is not possible to detail all the possibilities as it is still a growing field. For example, some complexes have been prepared in non-aqueous medium and (N2H5)2UF6 has been prepared by the reaction between UF6 and N2H5F in anhydrous hydrazine (Glavic and Slivnik 1970). The lanthanide hydrazine complexes with anions like halides, carbonate, nitrate, sulphate, perchlorate, acetate, oxalate (Schmidt 1984) and squarate(Vairam and Govindarajan 2006) have been prepared by the addition of hydrazine hydrate to the metal salts in an aqueous or alcoholic medium. 1.5 THERMAL REACTIVITY Thermal reactivity of the complexes varies from explosion → deflagration → decomposition depending upon the anion. Transition metal perchlorate, nitrate and azide hydrazines are primarily explosives, non-transition metal (Li+, Mg2+, Al3+) perchlorate, nitrate and azide hydrazines and transition metal oxalate, sulphite and hydrazine carboxylate hydrazine complexes deflagrate and the rest simply decompose with the loss of hydrazine. The deflagrating nature of metal hydrazines has been used in the preparation of ferrites (Gajapathy and Patil 1983) and cobaltites (Ravindranathan et al 1987). It is rather surprising that thermolysis of Mg(N3)2(N2H4)2 gave a blue coloured residue which showed a strong IR absorption at 2100 cm -1 characteristic of molecular nitrogen. The composition of the residue has been fixed as Mg(NH2)2N2 by chemical analysis and TG studies (Patil et al 1982). The tris-hydrazine complexes are considerably less stable both thermally and in air than the corresponding bis- hydrazine complexes. The complexes 17 M(XCH2COO)2(N2H4)3, (X = NH2- or OH- and M = Mn, Co, Ni, Zn or Cd) decompose violently above 200 °C in an exothermic single step to form metal powders (Sivasankar and Govindarajan 1994). Thus, thermal properties of the complexes differ depending on the composition, the metal ion, and type of the anion, the coordination mode of hydrazine and the atmosphere used in the experiments. 1.5.1 Thermal Decomposition of Metal Hydrazine Complexes Thermal decomposition of metal hydrazine complexes with a variety of anions such as halides, NCS- (Vittal 1981), NO3- and N3- (Patil et al 1982) have been studied. Depending upon the anion, the decomposition path changes dramatically (violently) giving mostly metal oxides as the final residue, whereas hydrazine complexes, M(N2H4)nX2 (Patil et al 1981, Glavic et al 1977, Glavic et al 1979 and Glavic et al 1980 ), to MX2, MOX2, MO, M2O3 or M. Thermal reactivity of MFe2(C2O4)3(N2H4)x, (Patil et al 1983), (M = Mg, Co, Ni or Zn and x = 5 or 6 ) and MFe2(N2H4)5(C2O4)3 (Gajapathy 1982) has been reported and these complexes decompose at low temperature to give ferrites as the final product. Preparation and thermal reactivity of MgC2O4(N2H4)2 (Patil et al 1982) have also been reported. Thermal decomposition of metal carboxylate hydrazines are more interesting due to their easier combustibility. For example, metal hydrazine formate (Ravidranathan and Patil 1983), acetate (Mahesh and Patil 1986), propionate, chloroacetate, glycinate and glycolate (Sivasankar 1994), oxalate (Patil et al 1982), malonate and succinate (Sivasankar and Govindarajan 1994), benzoate, salicylate (Kuppusamy 1995), trimellitate(Vairam et al 2010) and pyromellitate(Vairam et al 2010a) complexes have been studied by simultaneous DTA-TG-DTG thermoanalytical method. These complexes have been reported to decompose at lower temperatures than their non-carboxylate counterparts. Moreover, the oxalate complexes exhibit autocatalytic decomposition. This behaviour has been attributed to the simultaneous exothermic decomposition of hydrazine and metal salt (Patil et 18 al 1982). This phenomenon has been made use of in the preparation of fine particle ferrites (Gajapathy and Patil 1983) and cobaltites (Patil et al 1983) by the low temperature decomposition of M1/3Fe2/3(C2O4)(N2H4)2 (M = Mg, Mn, Co, Ni or Zn) and M1/3Co2/3(C2O4)(N2H4)2 (M = Mg or Ni), respectively. Large surface area CeO2 has been prepared by the thermal decomposition of cerium oxalate hydrazine complex. The thermal behaviour of metal maleate and fumarate hydrazine complexes have also been reported (Govindarajan et al 1995). The decomposition of nickel hydrazine glycinate complexes (Sivasankar 1994) have been reported to be violently exothermic and lead to explosion if the samples are heated in bulk. They give metal powder as the final product, even in air, unusually. Metal (Co, Ni and Zn) hydrazine phthalate complexes produce metal powder and benzoate, isophthalate and terephthalate complexes, the oxides as residue (Kuppusamy 1995). Metal hydrazine carboxylates decompose in air at a low temperature (75200°C) to yield fine particle oxide materials. Thermal M(N2H3COO)2.nH2O, (M = Ca, Mg, Mn, Fe, Co, Ni, Zn or Cu; studies on n = 0, 0.5, 1, 2, 3) are carried out extensively in air or inert atmosphere (Ravidranathan and Patil 1985, Macek and Rahten 1989, Macek and Rahten 1993, Braibanti et al 1967, Manoharan and Patil 1989). The thermal property of Nd(N2H3COO)3.3H2O in an inert atmosphere, (Macek and Rahten 1989, Macek and Rahten 1993) the synthesis of La(N2H3COO)3.2H2O and, thermal reactivity of Ln(N2H3COO)3.3H2O,(Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb or Y) and UO2(N2H3COO)2N2H4.H2O (Mahesh et al 1986) have been reported already. The decomposition is autocatalytic and accompanied by swelling due to the evolution of large amounts of gases like NH3, H2O, H2 and CO2. The preparation of γ-Fe2O3 and Co doped γ-Fe2O3 the commonly used recording material has been achieved by the thermal decomposition of iron hydrazine carboxylates in a single step. Similarly ultra fine ferrites and fine particle cobaltites have been obtained at very low temperatures by the thermal decomposition/combustion, of solid solution precursors (Ravindranathan and Patil 1987, Arunadevi et al 2009). 19 The thermal decomposition of metal sulphite hydrazine hydrates (Budkuley 1987) has been reported. The decomposition of mixed metal sulphite hydrazine occurs at low temperature due to high exothermicity of hydrazine decomposition in the complex. Iron is also known to catalyze the decomposition of hydrazine (Patil 1986). Hence these compounds undergo auto combustion once ignited. The thermal decomposition behavior of metal hydrazine sulphate was reported for the first time (Sivasankar and Govindarajan 1994). The thermal decomposition of the metal hydrazine phenyl acetate complexes have been reported (Jiji and Aravindakshan 1993). 1.5.2 Thermal Decomposition of N2H5+ and N2H62+ Metal Complexes The simultaneous TG-DTA studies of (N2H5)2M(SO4)2 ( M= Mn or Co) have been reported (Banerjee et al 1981). The complexes decompose exothermally at 275°C to MSO4 via an intermediate compound, M(N2H4)0.5HSO4(SO4)0.5. The thermal decomposition of (N2H5)2Mg(SO4)2, (N2H5)2M(SO4)2 and (N2H5)2M(SO4)2(N2H4)3 has been studied thoroughly (Patil et al 1981). The thermal properties of hydrazinium aluminium sulphate have been studied (Govindarajan and Patil 1982). Govindarajan et al, 1986 reported the thermal reactivity by TG -DTA methods of hydrazinium lanthanide sulphate hydrates, (N2H5)Ln(SO4)2.H2O. Thermal and structural studies on hydrazinium metal chlorides dihydrates were reported (Kumar et al 1991) and these complexes were found to yield metal oxide as the final residue via metal chloride. But the iron complex form FeO and the copper complex, Cu2O instead of the usual products Fe2O3 and CuO respectively. Slivink et al, 1968 and others have studied the thermal decomposition of N2H5+ and N2H62+ fluorometallates of transition metals (Frlec et al 1980, Frlec et al 1981, Slivnik et al 1966, Siftar and Bukovec 1970 and Bukovec et al 1971). The intermediate products of thermal decomposition are either hydrazinium(+1) fluorometallates, which further decompose to ammonium fluorometallates or 20 adducts of metal fluorides and hydrazine. It is observed that the formation of ammonium fluorometallates is highly exothermic. In all the cases, the final products of decomposition are metal fluorides, except in the case of copper complex, which forms the metal as the end product. Thermal behaviour of hydrazinium (+2) hexafluorogermenate has been studied (Gantar et al 1985). The thermal decomposition of some methyl hydrazine and methyl hydrazinium complexes of copper (II), copper (I) and mixed valence species has been studied by Dowling and Class, 1988. The simultaneous DTA-TG-DTG studies of hydrazinium metal formate hydrates of the formula, (N2H5)2M(HCOO)4.H2O, (M = Co, Ni or Zn) have been prepared (Sivasankar and Govindarajan 1995). The Co and Zn complexes form metal oxides and Ni complex forms metal as the final product of decomposition. Thermal behaviour of (N2H5)2M(CH3COO)4 (M = Co, Ni or Zn) has been reported (Sivasankar 1994). These complexes decompose at a lower temperature than the corresponding metal carboxylate hydrazine complexes. They have also studied the thermal behaviour of hydrazinium metal glycinates, malonate and mixed metal malonate dihydrates (M = Co, Ni or Zn). Glycinate complexes gave metal and the malonate complexes gave metal oxides as the final products of decomposition. The thermal behaviour of (N2H5)2M(C2O4)2.nH2O (M = Co, Ni or Cu and n = 3, 2 and 1 respectively) have been studied (Gajapathy et al 1983). Copper compound after melting undergoes exothermic decomposition whereas Co and Ni complexes decompose endothermally. Thermal studies of hydrazinium (+1) metal hydrazinecarboxylate hydrates, (N2H5)M(N2H3COO)3.H2O have been reported by a number of authors, at different periods, at different atmospheres viz., air, nitrogen or argon. Premkumar, 2002 who carried out the analysis in air and nitrogen atmosphere have reported the 21 formation of the metal oxides as the final products of decomposition. However, the authors (Macek and Rahten 1989 and Macek and Rahten 1993) who experimented the thermal decomposition in argon atmosphere for Fe, Co and Ni complexes have reported the metal powders as the end products, which are very reactive and sensitive to oxidation by the impurities in the argon. All of them decompose exothermally. 1.6 INFRARED SPECTRA OF HYDRAZINE, ITS SALTS AND COMPLEXES One of the best features of an infrared spectrum is that the absorption or the lack of absorption in specific frequency regions can be correlated with specific stretching and bending motions and in some cases, with the relationship of these groups to the remainder of the molecule. IR spectra of hydrazine and its derivatives are studied in the finger print region between 1300 cm-1 and 650 cm-1. They have been reported for several hydrazine derivatives (Savoie and Guay 1975, Glavic and Hadzi 1972) and metal complexes (Nieuwpoort and Reedijik 1973, Brown et al 1979, Braibanti et al 1968). Normal coordinate analysis for N2H2, N2H4, N2H5+, N2H62+ has been carried out (Mielke and Ratajczak 1973). Of special interest in the vibrational assignment of hydrazine is N-N stretching frequency, since the presence of this frequency, has been used as a criterion for determining the mode of bonding of hydrazine to metal ions as well as to distinguish it from N2H5+ and N2H62+ ions. Braibanti et al, 1968 have given a thumb rule on the basis of earlier studies. In the complexes examined by them and others, νN-N could be found at the following frequency ranges: 22 N2H4 (in solid state) 875 cm -1 N2H4 (unidendate) 930-940 cm -1 N2H4 ( bridging ) 948 - 985 cm-1 NH2NHY (Y = COO, CSS) 986-1012 cm-1 N2H5+ cation (non-coordinated) 960 - 970 cm-1 N2H5+ cation (coordinated) 990 - 1015 cm -1 N2H62+ cation 1020-1045 cm -1 Hydrazine as a unidentate ligand (Schmidt 1984), also shows N-N stretching at higher wave numbers, for example, 956 cm -1 in Мe3В.N2H4, 952 cm -1 in [Hg(N2H4)2]Cl2 or 950 cm -1 in SiF4(N2H4)2. Although the N-N stretchings for free N2H5+ and bridging N2H4 overlap, fixing the molecular formulae can identify them by analytical and other techniques. The assignment of the band at 875 cm -1 in the spectrum of hydrazine to νN-N was questioned by Durig et al (Durig et al 1966), who assigned this band to NH2 rocking vibration and the band at 1126 cm-1 to νN-N. The infrared spectra of M(N2H4)2Cl2 (M = Mn, Fe, Co, Ni or Zn) complexes were recorded (Satyanarayana and Nicholis 1978 ) and the absorption in the region 1150 -1170 cm -1 were assigned to νN-N of bridged hydrazine. Despite these reservations, the frequency of νN-N is a useful indication of the type of coordinated hydrazine. 23 1.7 STRUCTURAL STUDIES OF HYDRAZINE COMPOUNDS 1.7.1 Structure and Bonding in Hydrazine Infrared, Raman, microwave, NMR, photoelectron spectra and X-ray diffraction have been used to elucidate the structure and bonding of hydrazine (Shvo 1975 and Durig et al 1975). The high values of the melting point, boiling point and Trouton's constant of hydrazine indicate that it is extensively associated through an intermolecular H - bonding in the condensed phase, but monomeric in the gas phase. Electron diffraction data give N-N-H angle as 112° and N-N bond length as 1.45- 1.47 A° suggesting sp 3 hybridisation for the nitrogen atoms. Thus the two nitrogen atoms are joined by a σ-bond, rotation around which can give rise to one of the conformational isomers illustrated in Figure 1.1. Figure 1.1 The possible isomers of hydrazine (a) Staggered trans C2h (b) Eclipsed cis C2v (c) Semi-eclipsed half cis C2 (d) Gauche C The high value of dipole moment (Verstakov et al 1978) for hydrazine (1.83 -1.84 D) eliminates the trans (C2h) formation and the gauche form is 24 considered to be the equilibrium conformation as both the eclipsed and the semieclipsed conformations would involve coplanar repulsions. Electronic, infrared, Raman and microwave spectra show that the molecule has C2 symmetry in the vapour and liquid states (Durig et al 1975). However, X-ray and neutron diffraction investigations in the solid state show that the molecule to have either the gauche (C2) or cis (C2V) conformation. 1.7.2 Simple Hydrazine Compounds Two types of simple hydrazine compounds have been reported: (i) Simple molecular compounds of hydrazine of the formula, N2H4.nROH, where R = H, CH3 or C2H5, and n = 1 for H, 2 or 4 for CH3 and 2 for C2H5. (ii) Salts of hydrazine with HCl, HF, HBr, H2SO4, HCIO4, H3PO4, H2C2O4.2H2O, CH3COOH, 2, 3 pyrazinedicarboxylic acid, 3, 5pyrazoledicarboxylic acid etc. Extensive work has been done by Liminga and his coworkers (Liminga and Olovsson 1964, Liminga and Alex Mehlsen 1969 and Liminga 1967). The crystal structure of N2H5+C4H5O6- consists of infinite chain of tartrate anions linked by head to tail by O – H…O hydrogen bonds. Two such chains are cross-connected by O – H....O hydrogen bonds to form dimeric chains. The hydrazinium cation sits at the center of four tartrate dimers and bridges them by two center and three center N H....O hydrogen bonds. As a whole, the structure is stabilized by numerous hydrogen bonds. 25 1.7.3 Complexes Containing Hydrazine as a Unidentate Ligand The crystal structure of the Zn(N2H3COO)2(N2H4)2 and Co(N2H3COO)2(N2H4)2 are found to consist of chelates of the type as shown in Figure 1.2. NH2 H NH2 O C O NH2 N O C M N NH2 NH2 H O NH2 Figure 1.2 Structure of M(N2H 3COO)2(N2H4)2, where M= Co or Zn The hydrazine molecule, which acts as a unidentate ligand and the hydrazinecarboxylate anion, which acts as a bidentate ligand, are both coordinated in the trans position. The coordination around the metal is octahedral. Manganese and nickel form complexes isomorphous with zinc and cobalt analogues (Ravindranathan and Patil 1985). 1.7.4 Complexes Containing Hydrazine as a Bidentate Bridging Ligand Many stable complexes of metal salts with one, two or three hydrazine molecules are known, but their structures have so far received very little attention. 26 The only available crystal structures are on the complexes M(N2H4)2X2 (Ferrari et al 1963 and Ferrari et al 1965) (M= Mn, Co, Ni, Zn or Cd and X= Cl- (Ferrari et al 1963), NCS- (Ferrari et al 1965) and CH3COO- (Ferrari et al 1965). The above complexes have infinite chain structures (Figure 1.3) with cis bridging hydrazine molecules and respective anions in the trans positions. X X NH2 NH2 M M NH2 NH2 NH2 NH2 X X Figure 1.3 NH2 NH2 Structure of [M(N2H4)2X2]n where M= Mn, Co, Ni, Zn and Cd; X= Cl-, NCS– and CH3COO– It has been pointed out that chains of complexes are not held together by hydrogen bonds, thus favouring twinning which is observed in the crystals. Infrared (Sivasankar and Govindarajan 1994 and Braibanti et al 1968) and preliminary X-ray investigation of the complexes [M(N2H4)3]X2 (X= NO3-, H2NCH2COO-, HOCH2COO- and M = Mn, Fe, Co, Ni, Zn or Cd) appear to suggest a structure with three bridging hydrazine molecules linking metal ions which have an octahedral coordination. Recently, crystal structure of [Ni6(N2H4)6(SO4)4(OH)2(H2O)8](SO4)(H2O)10 has been determined. The structure of the complex is shown in Figure 1.4 27 Figure 1.4 Structure of [Ni6(N2H4)6(SO4)4(OH)2(H 2O)8](SO 4)(H2O)10 The complex cation in the compound has a remarkable structure with unusual diversity of bridging groups including hydrazine molecules, sulphate ions and hydroxo group (Gustafsson et al 2010). 1.7.5 Complexes with Bidentate Chelating (η2) Hydrazine The present crystallographically characterized complexes containing η2N2H4 are, [W(NAr)(N(NTs)2)Cl(η2 - N2H4)] (Cai and Schrock 1991) where Ar = 2,6-C6H3Pr2, N(NTs)2 = 2,6 –N(C5H3) (CH2Ts)2, [Cp*WMe3(η2-N2H4)]+(Schrock et al 1993), [Co(tripod)(η2-N2H4)]2+ (tripod = MeC(CH2PPh 2)3 and [Cp2*Sm(THF)(η2 -N2H4)]+ (Heaton et al 1996). As an example the structure of [Co(tripod)( η2N2H4)]2+ is given in Fig 1.5. 2+ CH3 P C P NH2 Co P NH2 Figure 1.5 Structure of [Co(tripod)(η2 -N2H4)]2+ 28 1.7.6 Compounds Containing N2H 5+ as a Ligand The crystal structure of iron complex, (N2H5)2FeCl4.2H2O has been studied (Kumar et al 1991). The complex consists of chloride ions and complex cation [Fe(N2H5)2(H2O)2Cl2]2+. The metal coordinated site in the molecule is a distorted octahedron made up of two nitrogen atoms (one from each N2H5+ ion), two oxygen atoms(from water molecule) and two chlorine atoms. The complex is found to be isomorphous with the corresponding Co, Ni and Cu analogues. The crystal structure of (N2H5)Nd(SO4)2.H2O has also been reported (Govindarajan et al 1986). Recently, crystal structure of {(N2H5)[Li3(C6H2N2O4)2(H2O)2].H2O}n has been reported(Starosta and Leciejewicz 2012). The structure is composed of molecular dimmers, each built up of two symmetry –related LiI ions with distorted trigonal - bipyramidal coordinations bridged by two deprotonated ligand molecules. The layers are held together by hydrogen bonds in which the hydrazinium cations coordinated and crystal water molecules act as donors and carboxylate O atoms acts as acceptors. The crystal structure of the complex (N2H5)2Co(NCS)4.2H2O has been studied (Kumar et al 1991). The crystal structure consists of discrete (N2H5)2Co(NCS)4 and H2O molecules. The cobalt ion is six coordinated by two hydrazinium and four thiocyanate ions. All the four thiocyanate groups are terminal N bonded. The structure of [Co(N2H5)2(NCS)4] is illustrated in Figure 1.6. The nickel complex is iso-structural with the cobalt complex. 29 + NH3 S S NH2 C N C N Co N NH2 C S N C NH3 + S Figure 1.6 Structure of [Co(N2H 5)2(NCS)4] The structure of the complex, (N2H5)2PtCl4.2H2O has been determined by a single crystal X-ray crystallography (Kumar et al 1991). This consists of [Pt(N2H5)2Cl2]2+ cations and water molecules. The platinum ion has a square planar coordination, bonded by two chlorine atoms and two nitrogen atoms from the N2H5+ ions through trans positions. Sivasankar and Govindarajan (Sivasankar and Govindarajan 1995 and Sivasankar 1994) have proposed an octahedral structure for [(N2H5)2MX4] (M = Co, Ni or Zn and X = HCOO-, CH3COO- and H2NCH2COO- and (N2H5)2M(OOCCH2COO)2.2H2O, (M = Co, Ni, Zn or Cd) on the basis of IR and electronic spectra, magnetic and thermal studies. Recently crystal structures of [Cr(N2H5)2(SO4)2](Parkins et al 2001), [Cd(N2H5)2(SO4)2](Srinivasan et al 2006) and [Mn(N2H5)2(SO4)2](Srinivasan et al 2007) have been determined. 30 1.7.7 Compounds Containing Non-coordinated N2H 5+ Ion Though N2H5+ ion is a potential coordinating group, in some compounds it behaves like the ammonium ion, i.e. it is outside the coordination sphere. The compounds with halides and hydrazinecarboxylate anions fall under this category. In the halide group the crystal structures of (N2H5)3CrF6 (Kojic-Prodic et al 1972), N2H5InF4.H2O (Bukovec and Golic 1976), N2H5LiBeF4 (Anderson et al 1973) and N2H5BeF3 (Anderson et al 1973a) have been determined. In these compounds N2H5+ ion is not coordinated to the metal ion. In N2H5LiSO4 also, N2H5+ is not coordinated (Anderson and Brown 1974) In the case of hydrazinium metal hydrazinecarboxylate hydrates, the crystal structure of N2H5[Ni(N2H3COO)3].H2O(Braibanti et al 1967) has been investigated. It has N2H5+ cation, complex anion and water molecules. In the complex anion, the nickel(II) is octahedrally coordinated by three bidentate hydrazine carboxylate anions. The crystals of the nickel compound, (N2H5)[Ni(N2H3COO)3].H2O are piezoelectric. The corresponding cobalt and zinc compounds are isomorphous with the nickel compound (Jesih et al 2004). A novel coordination mode for hydrazine carboxylate in a polymeric, ten-coordinate barium complex has been established crystallographically (Edwards et al 1993). The crystal structure of N2H5[Cu(C2O4)2].H2O (Gajapathy et al 1983) has revealed that the molecule contains discrete N2H5+ ions, [Cu(C2O4)2]2- ions and water molecules. It is shown in Figure 1.7. The same authors have reported the noncoordination of N2H5+ in (N2H5)2Co(C2O4)2.3H2O. 31 2O O C O O C O C Cu C O O O Figure 1.7 Structure of [Cu(C2O4)2] 2- anion Recently the crystal structure of (N2H5)2[Ln(pyzCOO)5].2H2O where Ln = La, Ce & (pyzCOO) = 2-pyrazine carboxylic acid and (N2H5)3[Ln(pyzCOO)4(H2O)].2NO3 where Ln = Pr, Nd, Sm and Dy have been synthesized(Premkumar et al 2009). The crystal structure consists of N2H5+ cations, La(pyzCOO)2- anions and water molecules. In these crystals, there are independent N2H5+ ions present in asymmetric unit and are not coordinated to the metal ion. The crystal structure of (N2H5)[Nd(C2O4)2(H2O)].4H2O and (N2H5)[Gd(C2O4)2(H2O)].4.5H2O have been synthesized(Arab et al 2005). The Nd atom is surrounded by nine oxygen atoms in which eight from four bidentate oxalate ions and one from aqua ligand. The coordination polyhedron around Nd(III) metal ion can be described as tri-capped trigonal prism. 1.7.8 Compounds Containing N2H 62+ Cation In this class of compounds N2H62+ ion exists as a cation to compensate the negative charges of the anionic complexes. Most of the compounds are known with fluoride anion and the crystal structures of (N2H6)[TiF6] (Kojic-Prodic et al 1971), N2H6SiF6 (Frlec et al 1980), N2H6[GeF6].H2O (Frlec et al 1981), N2H6[ZrF6] (KojicProdic et al 1971), (N2H6)2[TiF6]F2 (Golic et al 1980), N2H6[SnF3]2(Kaucic et al 32 1988), (N2H6)3[Zr2F13].F (Rahten et al 1990), N2H6[GaF5(H2O)](Meden et al 1996), (N2H6)[Ca(C7H2O6)2(H2O)2](Yasodha et al 2007)have been investigated. 1.7.9 Compounds Containing N2H 5+ and N2H 62+ Cations In this class of compounds two types of cations coexist in the atomic arrangement (hydrazinium(+1) ion, NH2-NH3+ and hydrazinium(+2) ion, NH3+NH3+). The crystal structure of (N2H5)2(N2H6)2P6O18 (Pouchot and Durif 1991) has been reported. 1.8 SCOPE AND OBJECTIVE The literature survey detailed so far illustrate the interaction of hydrazine hydrate with inorganic, aliphatic and aromatic carboxylic acids and metal ions leading to the formation of compounds with a variety of structures. With the view to understand the structure of metal complexes with carboxylic acids and functional group containing sulphur this work was undertaken. Moreover there is no report on sulphur containing carboxylic acids in the hydrazine system. In this work a systematic study has been carried out to find the results of interaction of hydrazine hydrate with the acids like thioglycolic, thiomalic, thiobenzoic and 5-sulphosalicylic acids in the presence of divalent metal ions like, Co2+, Ni2+, Zn2+, Cd2+, Cu2+, Hg2+ and Pb2+ and inner transition metal ions like, La3+, Pr3+, Nd3+, Sm 3+ and Gd3+ are reported. An attempt has also been made to use these complexes as precursors to prepare nano metal oxides. Single crystals are prepared using 5-sulphosalicylic acid with hydrazine and the structure has been found for the first time. For clarity the structure of acids and the different coordination modes of hydrazine are shown in Figure 1.8(a-d) and 1.9(a-c) respectively. 33 SH-CHCOOH COSH SHCH2COOH CH 2 COOH (a) Thioglycolic acid (b) Thiomalic acid (c) Thiobenzoic acid HO O HO S OH O O (d) 5-Sulphosalicylic acid Figure 1.8(a-d) Structure of the acids (a)Monodentate hydrazine (b)Bidentate hydrazine (c)Monodentate hydrazinium cation Figure 1.9(a-c) Structure of hydrazine 34 The main objectives of the present work are: To prepare hydrazinium salts of thioglycolic, thiomalic, thiobenzoic and sulphosalicylic acids and characterize them by analytical, IR spectroscopic, thermal analysis and single crystal XRD analysis To prepare metal hydrazine complexes of thioglycolic, thiomalic, thiobenzoic and 5 – sulphosalicylic acids by the reaction of hydrazine hydrate with metal nitrate hydrates, and characterize them by different physico-chemical techniques To correlate structure and thermal reactivity relationship among the complexes Hydrazine complexes are found to yield metal oxides at low temperatures in the nano scale, hence it was aimed to use the complexes to prepare nano metal oxides using them as precursors To find the conductivity of the complexes in their solid state To study the isomorphism among the complexes using powder X-ray diffraction technique To evaluate the kinetic parameters of dehydration and dehydrazination /decarboxylation of all the complexes and hydrazinium salts Based on the above objectives, this research work was performed and the results obtained are discussed in the following chapters.