X-Ray diffraction and spectroscopic studies of the light-induced metastable state of a ethylenediamine nitrosyl ruthenium complex

Blue-laser irradiation of a single crystal of the chloride salt of a cationic complex, trans-[Ru(en)2(H2O)(NO)]3+ (en = ethylenediamine), yielded MS1 (a metastable state of end-on type) which is remarkably stable (decay temperature Td = 267 K) compared with MS1 of sodium nitroprusside Na2[Fe(CN)5(NO)] (SNP). No MS2 state (side-on type) was observed by X-ray diffraction and IR spectroscopy. Even with a low population of 8% of the metastable species, the structure was clearly determined by X-ray analysis. For the first time, we observed an elongation of the N–O bond by X-ray diffraction, corresponding to a frequency downshift of the ν(NO) stretching vibration. The remarkably long lifetime of the metastable state of trans-[Ru(en)2(H2O)(NO)]3+ compared with that of SNP is explained by a stereochemical analysis using reaction cavity diagrams.