Electron-density studies of metal-metal bonds. I. The deformation density of Ti₂O₃ at 295 K

The electron-density distribution in Ti₂O₃ at room temperature has been determined from single-crystal X-ray diffraction data. The deformation maps show maxima of 0.15 e Å^-3 between the Ti atoms sharing a common face of O-atom octahedra, and maxima of 0.18 e Å^-3 between the O atoms and their four nearest Ti neighbours. These observations support the general view concerning the bonding in Ti₂O₃ and correlate well with the results of theoretical band-structure calculations. In particular, they confirm the existence of a metal-metal bond which is directed parallel to the ternary axis and is responsible for the anomalously low c/a ratio of this compound.