Photochemistry of Ruthenium II Complexes

Since saturated amine ligands lack lC orbitals, their photochemistry tends to be more straightforward to interpret because the ligand field bands are not obscured by more intense charge transfer bands. Some systems with heteroligands that have n orbitals will be considered here, but the important class of polypyridine complexes is deferred to the next section. 

The photolysis of Ru(NHj)g and Ru(en)3 was studied initially by Matsubara and Ford at pH 3 in 0.2 M NaCl. They found that aquation was the dominant process and the quantum yield of 0.25 for Ru(NHj) was constant between 313 and 405 nm. However, the quantum yield for Ru(en)3 decreased from 0.18 to 0.06 between 313 and 366 nm as yet there is no definitive explanation for this effect. More recently, Neumann and co-workers have used sensitizers and quenchers to study the Ru(NH3)g system. They concluded that the photoactive state is 17.3 0.4xl0 cm above the ground state and that it is the state. Although the spin-forbidden transition to this state has not been observed, it is predicted by theory to occur at 17.7x10 cm , i.e. 565 nm. 

For Ru (NH3)5X systems, the same pattern of photoactivity was observed for X = NCCH3, with quantum yields at 366 nm for loss of X and NH3 of 0.16 and 0.01, respectively. Loss of NH3 can yield cis and/or trans isomers, but the isomer distribution was not determined. More generally the redox 

There have been extensive studies on the family of complexes of the general type (H3N)3Ru(pyX) with a wide range of X substituents on the pyridine. The n oAital of the conjugated system in pyridine can interact with a d, orbital from Ru(II) to produce a bonding orbital and its antibonding partner The electronic transition from the ground state 

The photochemistry of (H3N)5Ru(py) has been intensively studied because it is a prototype for the polypyridine systems described in the next section, and because it has an unusual [H ] dependence. The accepted mechanism for the dominant pathway is shown in the following scheme  

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