Antithermal pathway

Photosubstitution reactions and quantum yields of aq Rh(III) and Ir(IlI) complexes are summarized " in Tables 1 and 2. Each of these complexes has a ligand-field (LF) state as the lowest-energy excited state in HjO, and ligand labilization occurs with moderate to high quantum yields. In several cases, the antithermal pathways dominate, e.g., LF photolysis of the halopentaammines gives both the normal thermal reaction, i.e., halide aquation, and an antithermal pathway, ammine aquation ... 

If a Co "(NH3)jX complex is photolysed by irradiation into the d-d bands (wavelength 450 nm), then photoaquation is observed with low quantum yields in the range of 1x10" to 1x10". These reactions show a significant antithermal pathway in which NH, is released to yield Co(NH3)4(OH2)X mainly as the trans isomer. Some examples of quantum yields for the two paths are given in Table 7.2. 

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