The First Photocrystallographic Evidence for Light-Induced Metastable Linkage Isomers of Ruthenium Sulfur Dioxide Complexes

Light-induced metastable linkage isomers of trans-[Ru(NH3)4Cl(SO2)]Cl and trans-[Ru(NH3)4(H2O)(SO2)](C6H5SO3)2 have been identified for the first time using photocrystallographic methods. In both
linkage isomers the SO2 ligand is side bound, but the Ru−O and Ru−S distances are considerably longer
and almost equal in the trans-H2O isomer. DFT calculations confirm that both isomers correspond to minima
on the ground-state potential energy surface and also predict the existence of a second oxygen-bound
isomer for both compounds. The decay of the light-induced species has been studied by both DSC and IR.
Activation energies for the thermal back-reaction, as derived from the temperature-dependent disappearance
of light-induced IR bands, are 50.0 and 58.4 kJ/mol for the two isomers, which is larger than the
corresponding numbers for photoinduced side-bound nitrosyl linkage isomers.