Thermochimica Acta, Vol.274, 139-148, 1996
Preparation and Thermal Reactivity of Hydrazinium Uranyl Carboxylates
Hydrazinium uranyl carboxylates with the formula N2H5[UO(2)L(3)]. nH(2)O, where for L = salicylate, n = 4; for L = benzoate and p-hydroxybenzoate, n = 2; for L = hydrazinecarboxylate, n = 1; for L = acetate, propionate and thioglycolate, n = 0, and dihydrazinium uranyl phthalate (N2H5)(2)[UO2(o-C(6)H4(COO)(2))(2)] have been prepared in aqueous media. The electronic spectra of the complexes confirm the presence of the uranyl cation in the molecules. The infrared spectra of the complexes show the N-N stretching frequency of N2H5+ in the range of 970-980 cm(-1) confirming its ionic nature. The small separation (Delta v < 150 cm(-1)) between the asymmetric and symmetric stretching vibrations of the carboxylate groups in all the complexes except hydrazinecarboxylate and phthalate compounds, reveals the bidentate chelate coordination of the carboxylate groups. The hydrazinecarboxylate group is coordinated through O and N atoms as a bidentate chelate. IR frequencies also show that one of the carboxylates in the phthalate complex is a monodentate and the other is bidentate chelate. Thus the phthalate ligand bridges in both uni- and bidentate fashion. Simultaneous TG-DTA shows that the aromatic carboxylate complexes, including hydrazinium uranyl hydrazinecarboxylate monohydrate, decompose exothermically whereas the aliphatic counterparts decompose both endo- and exothermically. Except for N2H5[UO2(N2H3COO)(3)). H2O all other complexes decompose via uranyl carboxylate intermediate to give U3O8 as the final product. The water molecules are lost endothermically at low temperature (around 100 degrees C) indicating the presence of water molecules as water of crystallisation.