Photochemical aquation chromium complexes

The major contributions falling within the scope of this section are those of Frankel, Langford, King and others,who have concentrated on the thermal and photochemical reactions of chromium(III) complexes. Additional interesting results relevant to cobalt(III) aquation reactions have been produced by Barraclough and McTigue " while a recent review by Amis on the solvation of a range of main block elements is relevant. 

Mixed-ligand complexes of chromium(III) also undergo photoaquation reactions. In general, two or more photoreactions occur simultaneously, and the predominant product from the photochemical reaction may be different from the product that is obtained under thermal conditions. An example of such difference in regioselectivity is observed with the halo complexes CrX(NH3)s. Under thermal conditions, aquation of the halide ion (X") is the preferred pathway ... 

Several examples are known of the effectiveness of organic compounds sensitizing photochemical reactions of cobalt(m) and of chromium(m) complexes, and biacetyl is known to photosensitize the aquation of [PtCU] ". Now the first example of photosensitization of substitution at platinum(n) by an inorganic species has been reported [Ru(bipy)3] + sensitizes photoaquation of the [PtCl4] anion. ... 

Solvation.— The dependence of the reactivity of a complex on the composition of its solvation shell can only rarely be satisfactorily probed. In the case of chromium(m) complexes n.m.r. (and occasionally u.v.-visible) spectroscopy can often reveal the composition of the solvation shell, so that this can be correlated with reaction rates. This treatment was first fully developed for the solvolysis, both thermal and photochemical, of the [Cr(NCS)6] anion in aqueous acetonitrile, as described at some length in Volume 1 of this Report. The approach has subsequently been found useful and informative in investigations of aquation and of isomerization of the [Cr(ox)3] anion in aqueous... 

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