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

The isostructural hexaaquatransition-metal/titanium citrate complexes (NH 4) 2[ M(H 2O) 6][Ti(H 2cit) 3] 2·6H 2O [ M(II)=Mn 1, Fe 2, Co 3, Ni 4, Cu 5, and Zn 6] (H 4cit=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 MgTi 2O 5 that is of the pseudobrookite type; the particle size is approximately 30 nm. A 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 MTi 2O 5.