Synthesis and characterization of homo- and heterobimetallic niobiumv and tantalumv peroxo-polyaminocarboxylato complexes and their use as single or multiple molecular precursors for Nb–Ta mixed oxides

New water-soluble bimetallic peroxo complexes of niobiumV and/or tantalumV with high-denticity polyaminocarboxylate ligands have been prepared, characterized from the spectroscopic point of view, and used as molecular precursors for Nb–Ta mixed oxides. Four new homobimetallic complexes, (gu)3[Nb2(O2)4(dtpaO3)]·3H2O 1, (gu)3[Ta2(O2)4(dtpaO3)]·5H2O 2, (gu)3[Nb2(O2)4(HtthaO4)]·2H2O 4 and (gu)3[Ta2(O2)4(HtthaO4)]·3H2O 5 and the corresponding heterometallic complexes, (gu)3[NbTa(O2)4(dtpaO3)]·2.5H2O 3 and (gu)3[NbTa(O2)4(HtthaO4)]·2H2O 6 have been obtained. In these compounds, the in situ oxidation of the nitrogen atoms of the PAC ligands into N-oxide groups has been evidenced by IR spectroscopy and mass spectrometry. The thermal treatment of the homonuclear complexes in air at 700 or 800 °C, depending on the Ta content, provided Nb2O5 or Ta2O5 while the heteronuclear compounds led to the solid solution TaNbO5. BET and SEM measurements have been carried out and comparison of the morphology of the samples prepared from homo- and heterometallic precursors is discussed.