Titanium-based mixed oxides from a series of titanium(IV) citrate complexes

The isostructural hexaaquatransition-metal/titanium citrate complexes (NH4)2[M(H2O)6][Ti(H2cit)3]2·6H2O [M(II)=Mn 1, Fe 2, Co 3, Ni 4, Cu 5, and Zn 6] (H4cit=citric acid), which were synthesized by reacting titanium(IV) citrate with divalent metal salts in the 1.0–3.5 pH range, adopt hydrogen-bonded chain motifs. The crystal structures feature three bidentate citrate anions that chelate to the titanium atom through their negatively charged α-alkoxy and α-carboxy oxygen atoms; the chelation is consistent with the large downfield shifts of 13C NMR for carbon atoms for complex 6. The thermal decomposition of the complexes furnishes mixed metal oxides. The main-group magnesium analog when heated at 600 °C yielded MgTi2O5 that is of the pseudobrookite type; the particle size is approximately 30 nm.

Graphical abstractA series of heterobimetallic titanium citrate complexes with novel dodecameric water clusters were isolated and used as molecular precursors in an attempt to the preparations of mixed oxides MTi2O5.Figure optionsDownload full-size imageDownload as PowerPoint slide