Single-source materials for metal-doped titanium oxide: Syntheses, structures, and properties of a series of heterometallic transition-metal titanium oxo cages

Titanium dioxide (TiO ) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt) with transition-metal dichlorides (M Cl , M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti O(OEt) (MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi (μ -O) structural arrangements involving ion pairing of [Ti O(OEt) ] anion units with MCl fragments. In the case of the reaction of MnCl , however, two Mn ions are incorporated into this framework, giving the hexanuclear Mn Ti (μ - O) cage [Ti O(OEt) (Mn Cl )] (6) in which the MCl fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl] unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt) with NiCl gives [Ti (OEt) (NiCl)] (7), which has a dimeric Ni(μ-Cl) Ni bridged arrangement arising from the association of [Ti (OEt) ] ions with NiCl units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials.