Pentachloro- and pentabromo-titanate(IV) ions

Abstract

The reactions between titanium(IV) chloride and tetra-alkylammonium chlorides and between titanium(IV) bromide and tetra-alkylammonium bromides, in solution in dichloromethane, have been studied by Raman and i.r. spectroscopy. The five-co-ordinate ions [TiCl₅]^– and [TiBr₅]^– have been clearly identified for the first time. These ions and the other singly charged species [Ti₂Cl₉]^– and [Ti₂Br₉]^– are the only anions detected by Raman spectroscopy in the dichloromethane solutions. The preparations of the tetrabutylammonium salts [Bu₄N][TiCl₅] and [Bu₄N][TiBr₅] and of tetraphenylarsonium pentachlorotitanate are described, but the corresponding salts of the smaller tetraethyl- and tetrapropyl-ammonium cations are shown to be [Et₄N]₂[Ti₂Cl₁₀], [Et₄N]₂[Ti₂Br₁₀], and [Pr₄N]₂[Ti₂Cl₁₀] with binuclear halogen-bridged anions.