Halides of Titanium in Lower Oxidation States

Abstract

New investigations on the di- and trihalides of titanium, TiX₂ and TiX₃ (X = Cl, Br, I), with their 3d² and 3d¹ electronic configurations, confirm the early observations and conclusions of Klemm. At sufficiently low temperatures, Ti–Ti single bonds are formed in the one-dimensional trihalides, i.e., Ti–Ti dimers are observed. Equally, in the two-dimensional dihalides, {Ti₃} triangles occur with three single bonds. Phase transitions were detected from single-crystal or powder X-ray diffraction data, from magnetic measurements and thermal analysis. Except for the binary halides a number of ternary halides ATiX₃ (extended chains of facesharing octahedra), K₄Ti₃Br₁₂ (triples of face-sharing octahedra), Na₂Ti₃Cl₈ (triangular trimers), A₃Ti₂X₉ (dimers of face-sharing octahedra), and A₃TiX₆ (isolated octahedra) as well as the mixed-valent halides CsTi₂I₇ (tetrahedra and octahedra) and Na₅Ti₃Cl₁₂ (chains of octahedra) have been observed. Except for the triangles in titanium(II) halides, cluster compounds are rare but include K₄[{OTi₄}I₁₂] and {CTi₆}Cl₁₄.