The IR and Raman spectra and the thermal behaviour of the isomorphous compounds (NH4)3Ga(C204)a. 3H20 and (NH4)3Al(C204)3-3H~O were investigated. Detailed stoichiometries, sustained by TG, DTA and IR spectroscopic analyses, were found in both cases. Different results, associated with the different polarizing powers of the metal cations, were obtained. The first evidence was found of the formation of basic gallium carbonates.The isomorphous salts (NH4)3Ga(C204) 3 9 3H20 and (NH4)3Ai(C204) 3 9 3H20 belong to the triclinic system, space group PI and Z = 2 [1]. In these compounds the Ga and the AI atoms are coordinated by six oxygen atoms from oxalate groups, in the form of a distorted octahedron [1]. These polyhedra are linked together by hydrogen-bonding. The three oxalate groups act as bidentate ligands, and the bond lengths and bond angles are similar to the values found for other oxalato complexes [1]. A peculiarity of these structures is the non-equivalence of the water molecules. They seem to be situated at several different sites in the lattice. Consequently, the characteristics of the hydrogen-bonding are unclear. Further, the gallium and aluminium compounds are structurally different from the similar compounds of other elements of group III. The coordination number for In(Ill) in the same stoichiometry is eight, and that for Y is nine [2,3].As the polarizing powers of Ga(III) and AI(III) differ in magnitude, one might expect that their complex salts will differ in thermal behaviour.I R spectroscopy can be used to characterize the constitution of the intermediates generated during the pyrolysis process.On the other hand, fhe vibrational behaviour can contribute to a better knowledge of the properties of the M---O bonds and their effects on other bond lengths and bond strengths.
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