In Situ Surface-Enhanced IR Absorption Spectroscopy on CO Adducts of Iron Protoporphyrin IX Self-Assembled on a Au Electrode

• Published in: The journal of physical chemistry. B Vol. 110; no. 30; pp. 14911 - 14915
• Main Authors: Ma, Min, Yan, Huo, Sheng-Juan, Xu, Qun-Jie, Cai, Wen-Bin
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 03.08.2006
• Subjects: Carbon Monoxide - chemistry; Electrodes; Gold - chemistry; Metal Nanoparticles - chemistry; Protoporphyrins - chemistry; Spectroscopy, Fourier Transform Infrared - methods
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp061962g

The surface coordination chemistry of carbon monoxide with the reduced form (FeIIPP) of iron(III) protoporphyrin IX (FeIIIPP) monolayer self-assembled on a Au electrode in 0.1 M HClO4 was studied for the first time by using in situ ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Both mono- and biscarbonyl adducts [simplified as FeII(CO)PP and FeII(CO)2PP, respectively] were detected, depending on the history of potential control. Initially, the FeII(CO)PP predominates, and the intermediate transition potential for the conversion of FeII(CO)PP to FeIIIPP and CO was spectrally determined to be ca. 0.09 V (vs SCE). The ratio of FeII(CO)2PP and FeII(CO)PP increases after a potential excursion to a sufficiently positive value. FeII(CO)2PP is much more stable against its electro-oxidation to FeIIIPP than its counterpart FeII(CO)PP with increasing potential. The observed change of coordination properties may be ascribed to an irreversible structural reorganization of the FePP adlayer caused by the potential excursion.