Hydroxo-bridged complexes of chromium(III), cobalt(III), rhodium(III), and iridium(III)

Publisher Summary Polynuclear complexes with hydroxide (or oxide) as bridging ligands constitute an important class of complexes. They are formed by hydrolysis of mononuclear aqua complexes of most metal ions and, therefore, constitute an important aspect of the hydrolytic chemistry of metal ions. They display a chemistry which is interesting and is also relevant in relation to applied chemistry and to biochemistry. This chapter reviews the chemistry of hydroxo-bridged chromium(III), cobalt(III) complexes, and includes studies of the related rhodium(III) and iridium(III)systems. The review focuses the chemical properties of these complexes, and special emphasis has been made on reactions that involve the cleavage or formation of a hydroxo bridge. Reactions of bridging groups other than hydroxide and reactions of nonbridging ligands are also discussed in the chapter. A large number of X-ray crystal-structure determinations have been made during the past two decades. The hydroxo-bridged chromium(III) oligomers constitute a very interesting class of complexes from a spectroscopic and magnetochemical point of view. The most important methods for obtaining structural information about solutions are probably potentiometric pH measurements and visible/ultraviolet spectroscopy, but many other techniques have been applied, including bridge-cleavage experiments, magnetic measurements, and electron spin resonance (ESR) spectroscopy.