Some Recent Developments in the Chemistry of Transition Metal Oxocations

The range of stability of transition metal oxocations in aqueous solution is discussed. Species with a metal‐oxygen bond of order higher than unity are particularly interesting. Bond orders can sometimes be determined from bond lengths and angles, but generally only by infrared spectroscopy. – The frequency range of the metal‐oxygen stretching vibration, previously assumed as about 900–1100 cm −1 , must according to these investigations be extended at least to 780 cm −1 if all multiple bonds, particularly those in trans‐dioxo complexes, are to be included. Broad bands down to 650 cm −1 are ascribed to metal‐oxygen bridges. — The existence of cations such as ZrO 2+ and VO , or of the “well‐known” titanyl ion, TiO 2+ , has never been proved. In many cases polynuclear, oxygen‐bridged oxometal species must be assumed.