Ammonium dioxoperoxymalonato Uranate (VI) tetrahydrate was obtained by reaction of Uranyl nitrate (U O2(N O3)2) with Malonic acid (CH2(COOH)2), and then Hydrogen peroxide (H2O2) in the presence of Ammonium ion (NH4 +). The complex was subjected to chemical analysis. The chemical analysis of the complex was performed by using elemental analyzer and thermogravimetric techniques such as Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Differential Thermogravimetric Analysis (DTG). The complex and the intermediate products of its thermal decomposition were further characterized by using Infrared (IR) absorption and X-ray diffraction spectra. Based on the data from these physico-chemical investigations, the structural formula of the complex was proposed as (NH4)2[UO2(O2)(H2C3O4)].4H2O.

Uranyl ion (UO₂²⁺) forms numerous complexes with different mono and bidentate ligands such as sulphate (SO₄^2-), carbonate (CO₃^2-), oxalate (C₂O₄²) and malonate (CH₂(COO)₂^2-) ions. The present work emphasizes the synthesis and characterization of 1:1 complex species. The 1:1 Peroxyuranates have been reported in literature (Keller, 1975). Of these, the compounds with the chemical formula MIHU₂O₉.nH₂O, M₂ IU₂O₉.nH₂O and M₂UO₅.nH₂O were found to be important (DeMarco et al., 1959). These compounds were obtained either by the action of uranyl nitrate on alkaline Hydrogen peroxide (H₂O₂) or as decomposition products of alkaline solutions of triperoxy uranates. The uranyl complexes of a maleonitrile containing ligand (Helen et al., 2011) and its structural, spectroscopic and redox properties were explained. A trigonal coordination geometry was proposed for the UO₂ ²⁺ in the complex of p-tertbutylhexahomotrioxacalix[ III]arene (Pierre et al., 1999). The salophen and oxine as chromophoric ligands of uranyl complexes were also mentioned in literature (Horst and Arnd, 2002). Peroxometal compounds of uranyl ion (Van et al., 1987) and their practical use (Olah and Welch, 1978) were reported. The synthesis and characterization of urnayl complexes with a tetradentate methylterephthalamide (Chengabao et al., 2011) and with three isomeric methyl-pyridine-N-oxide ligands were also reported (Alvarenga et al., 2004). The other peroxoactinide complexes were also studied (Westland and Tarafdar, 1981; Basumatary et al., 1986; and Bhattacharjee et al., 1986). Uranyl complexes with new binucleating ligands (Gandhi and Kulkarni, 1999) and mono dentate nitrogen ligands (Olga et al., 2011) were also reported. The synthesis and characterization of uranyl complexes of aminoalcoholbis (phenolate) [O,N,O,O’] donar ligands (Hari et al., 2006) and the ternary complexes of uranyl beta-diketones with aliphatic amides (Ruikar et al., 1991) were also reported. Synthesis and characterization of dinuclear mixed ligand peroxouranium (VI) complexes (Chitra and Alok, 1997) and oxasapphyrin-uranyl complex (Jonathan and Andreas, 1998) were reported. The author has already reported the thermal decomposition behavior of barium dioxodiaquaperoxyoxalat uranate (VI) tetrahydrate (Sailaja et al., 2002).

In the present study, ammonium dioxoperoxymalonato uranate (VI) complex was prepared by the reaction of UO₂ ²⁺with Malonic acid (CH₂(COOH)₂), and then H₂O₂ in the presence of Ammonium ion (NH₄ +). The thermal decomposition mechanism is explained on the basis of Thermogravimetric (TG) analysis, Infrared (IR) spectroscopic and X-ray diffraction data of the complex.

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