Thermal behaviour of some Al(III)-Mg(II) polynuclear coordination compounds with polycarboxylic acid anions as ligands, precursors of aluminates

A TG, DTG and DTA study of three polynuclear coordination compounds, containing Al(III)-Mg(II), namely (NH4)4[Al2Mg(C4O5H4)4(OH)4]⋅2H2O, (NH4)4[MgAl2(C4H4O6)4(OH)4]⋅3H2O and (NH4)2[Al2Mg(C6O7H11)5(OH)5]⋅3H2O, has been reported together with the associated thermal decomposition mechanism rationalized in terms of intermediate products. As decomposition end-product, magnesium-aluminum spinel is obtained. The values of MgAl2O4 mean crystallite size depend on the anionic ligand contained by the precursor compound, varying in the order: malate (143 A) ligand contained by the precursor compound, varying in the order: malate (143 A)