Comparative IR Study of Nitric Oxide Reactions with Sublimed Layers of Iron(II)− and Ruthenium(II)−meso-Tetraphenylporphyrinates

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Abstract
The interactions of nitric oxide gas with thin layers of FeII(TPP) and RuII(TPP), obtained by sublimation onto low-temperature substrate (77 K), has been investigated by means of IR spectroscopy (TPP = meso-tetraphenylporphyrinate). Only simple addition of NO to form Fe(TPP)(NO) is observed for the iron−porphyrin FeII(TPP), while, in contrast, RuII(TPP) promotes NO disproportionation to form the nitrosyl−nitrito complex Ru(TPP)(NO)(ONO) and N2O. Thin layers of Fe(TPP)(NO) are inert to further reaction with excess NO; however, the nitrosyl−nitro complex Fe(TPP)(NO)(NO2) is readily formed when traces of dioxygen are added to the NO atmosphere. When the NO2 concentrations in the NO/NO2 mixture are relatively high, the nitrato complex Fe(TPP)(NO3) is also formed. Spectral data are given indicating that moderate shifts in the nitrosyl stretching frequency of Fe(TPP)(NO) are due to crystal packing effects, rather than to the H-bonding of coordinated NO with protic contaminants suggested in an earlier publication. Removal of NO by exhaustive evacuation from layers containing Fe(TPP)(NO)(NO2) leads to formation of Fe(TPP)(NO) and Fe(TPP)(NO3).

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