Thermogravimetric study of the scandium nitrate hexahydrate thermolysis and computer modeling of intermediate oxynitrates

The thermal decomposition of scandium nitrate is a complex process, which begins with the simultaneous condensation of 4 mol of the initial monomer Sc(NO 3 ) 3 ·6H 2 O. The resulting cyclic tetramer Sc 4 O 4 (NO 3 ) 4 ·2H 2 O gradually loses azeotrope H 2 O–HNO 3 , and an intermediate oxynitrate Sc 4 O 5 (NO 3 ) 2 is formed. At higher temperature, this oxynitrate is destroyed leaving behind unstable dimer Sc 4 O 6 which is transformed into scandium oxide. The molecular mechanics method used for comparison of the potential energies of consecutive products of thermal decomposition permits an evaluation of their stability and a proper interpretation of experimental data. The structural modeling was aimed to provide detailed information about the bond lengths and bond angles, filling the gap in what we know about amorphous oxynitrates. The models represent a reasonably good approximation to the real structures.