On the photochemical behavior of the [Ru(NH3)(4)(NO)nicotinamide](3+) cation and the relative stability of light-induced metastable isonitrosyl isomers of Ru complexes

Low-temperature IR experiments on crystalline samples of trans-[Ru(NH3)(4)( NO) nicotinamide](3+) salts show a light-induced absorption band typical fo r MS 1 NO linkage isomers upon exposure to 300-500 nm light from a Xe sourc e. The formation of a metastable species is confirmed by DSC measurement on a sample irradiated at low temperature with 457 nm light from an Ar+ laser . The light-induced species decays between 250 and 260 K according to both IR and DSC results. This decay temperature (Td) is somewhat below that obse rved for other high-Td linkage isomers, even though the NO-stretching frequ ency of the of [Ru(NH3)4(NO) nicotinamide](3+) ion is above that of the oth er isomers, demonstrating a lack of precise correlation between the two phy sical properties. The 90 K crystal structure of trans-[Ru(NH3)(4)(NO)nicoti namide](SiF6)(NO3).H2O is reported. The geometry from theoretical DFT calcu lations of the ground-state structure agrees well with the experimental res ults, except for the orientation of the CONH2 substituent in the pyridine r ing, which is rotated by 180 degrees in the crystal due to packing effects. The MS1 and MS2 linkage isomers are found to correspond to local minima on the ground-state potential energy surface, and their geometries and energi es are reported.