Halides of Titanium in Lower Oxidation States

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.