Photochemistry of Chromium lll Ammine Compounds

One of the more classical examples of inorganic photochemistry includes the photoaquation reactions of Cr(lll) ammines. The generic reaction is shown in Equation (17.57), but a variety of N-coordinating ligands can be substituted for NH3 in this expression and sometimes another ligand other than NH3 is dissociated. 

Some selected Cr(lll) ammines, their photochemical products, and the quantum yields for product formation are listed in Table 17.17. 

Some general observations about the data in Table 17.17 follow  

Although the Cr(lll) ground state is substitutionally inert (d ), the quantum yields for the photochemical processes are rather large. 

The photochemical product differs from the thermal product in most cases and occurs I0 -I0 times faster For example, the thermal product for aquation of [Cr(NH3)rCI] + is [Cr(NH3)5(H20)] , while the photochemical product is c/s-[Cr(NH3)4(H20)CI]2+. 

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