The conditions of thermal decomposition of scandium(l I I) hemimellitate, trimellitate and trimezinate in air and nitrogen atmospheres have been studied. On heating, the benzenetricarboxylates of Sc(lll) decompose in two stages. First, the hydrated complexes lose crystallization water; heating in air finally yields Sc20 3, and heating in a nitrogen atmosphere Sc20 3 and C. The dehydration of the complexes is associated with strong endothermic effects. Thedecomposition of benzenetricarboxylates in air is accompanied by an exothermic effect and in nitrogen by an endothermic effect.The activation energies of the dehydration and decomposition reactions have been calculated for the Sc(I I I) benzenetricarboxylates. (lll) have not been studied so far. As a continuation of our work on the thermal decomposition of scandium(Ill) carboxylates [5][6][7], we now report the thermal decomposition of scandium(l I I) benzenetricarboxylates in air and nitrogen atmospheres.
ExperimentalScandium(Ill) benzenetricarboxylates were prepared in double decomposition reactions by adding ammonium hemimellitate (pH 5.8), trimellitate (pH 4.6) or trimezinate (pH 5.6) to a hot solution containing Sc(lll)nitrate (0.1 M). The precipitate formed was heated in the mother liquor for 1 h, then filtered off, washed with water to remove NH~ ions and dried at 30 ~ to constant mass.
The multi-step dehydration and decomposition of trivalent lanthanum and lanthanide heptanediate polyhydrates were investigated by means of thermal analysis completed with infrared study. Further more, X-ray diffraction data for investigated heptanediate complexes of general stoichiometry Lnz(CTHt004)3.nH20 (where n = 16 in the case of La, Ce, Pr, Nd and Sm pimelates, n = 8 for Eu, Gd, Tb, Dy, Er and Tm pimelates, n = 12 for Ho, Yb and Lu pimelates) were also reported.The last discoveries of new properties and oceurence of heptanedioie acid (usually called pimelic acid) and its compounds have indicated many possibilities of their practical use [1][2][3][4][5][6][7]. It is well known that heptanedioic acid durint heating undergoes a variety of transformations such as decarboxylation, eyclization and polymerization. Its complexes play a dominant role in biochemical systems and are used for preparation of some sorts of bactericides and antibiotic substances [8,9]. The salts of heptanedioic acid show the antidiabetic activity [10]. Pimelie acid inhibits the development of saprophytic mieroflora, and for that reason is used now for biological purification of wastewater from the production of synthetic fat [11].Heptanedioic acid as bidentate ligand forms easily eomplexes with a vide variety of metals; however only few data exist in literature on lanthanide pimelates. The preparation of these complexes and their solubility in water are published by Ryabehikov [12]
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