Chromium complexes hydroxy-bridged

The vanadium(iii) ion [V(H20)6] (9.9) exhibits this behaviour, with a log AT of 4 associated with the formation of the hydroxy-bridged dinuclear complex 9.10. This is a general phenomenon. For example, chromium(iii) and iron(iii) form strictly... 

The coordination chemistry of chromium(III) was first seriously investigated by Pfeiffer at the turn of the century in many ways his studies parallel the work of Werner on cobalt(III). The complexes of chromium(III) are almost exclusively six-coordinate with an octahedral disposition of the ligands. Many are monomeric ((Jeff 3.6 BM), although hydroxy-bridged and other polynuclear complexes are known in which spins on neighbouring chromiums are coupled. 

An extensive, if somewhat dated, review of the coordination chemistry of aromatic TV-oxides is available.954 Most studies of the A-oxide complexes of chromium(III) involve the preparation and characterization (usually by magnetic and spectroscopic methods) of monomeric or hydroxy-bridged complexes and are summarized in Table 84. 

Picolinic acid (pyridine 2-carboxylic acid) complexes of chromium(III) have been the subject of a number of studies. Complexation by picolinic acid in water/ethanol (30% v/v) follows an ion-pairing, Eigen-Wilkins type mechanism.Activation parameters suggest an associative character for the reaction of the aqua complex. Chelated complexes of chromiuni(ni) and picolinic acid are the products of the rapid, inner-sphere reduction of [Co (pico)(NH3)5p with chromium(II). The reaction of the related 4-carboxylic acid complex of cobalt(III) with chromium(II) is also rapid in contrast, pyridine-3-carboxylic acid (nicotinic acid) complexes undergo slower reactions. A -hydroxy-bridged dimeric complex [Cr2(pico)4(OH)2] has also been prepared. A study of magnetic properties in the temperature range 16-300 K leads to J - —6 cm and g = 2, typical for such complexes. 

Ferraro, J. R., R. Driver, W. R. Walker, and W. Wozniak, 1967. Infrared spectra of several hydroxy-bridged complexes of chromium (III) and iron (III) from 650 to 80 cm" Inorg. Chem. 6 1586. 

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