The Structure of the FeNO Group in Two Metastable States (MS1 and MS2) of the Nitroprusside Anion in Na2[Fe(CN)5NO]-2H20. Infrared Spectra and Quantum Chemistry Calculations for the Normal and the 15NO and N18O Isotopic Substituted Substance

Low temperature infrared spectra of light induced metastable states MS1 and MS2 of the nitroprusside anion in Na2(Fe(CN)5NO]-2H20, isotopically normal and substituted with 15NO and N18O, are presented and discussed. As a consequence of the relatively high population of the MS2 state achieved by further irradiation with 1064 nm light of samples previously irradiated with 488.0 nm light, new bands were seen for the first time, and others, previously reported, were confirmed. The comparison of the spectral data obtained for the FeNO moiety of the isotopically normal as well as of the 15NO and N18O substituted anion with the results of quantum chemical (DFT) calculations support the assignment of the bands which appear after successive irradiations to MS1, the linear Fe(eta1-ON) linkage isomer, and to MS2, the side-bound Fe(eta-NO) isomer.