Article,

Spectroelectrochemical Evidence for the Nitrosyl Redox Siblings NO+, NO., and NO- Coordinated to a Strongly Electron-Accepting FeII Porphyrin: DFT Calculations Suggest the Presence of High-Spin States after Reduction of the FeII-NO- Complex

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Chemistry - A European Journal, 17 (28): 7868-7874, S7868/1-S7868/9 (2011)
DOI: 10.1002/chem.201003516

Abstract

Exptl. and computational results for the electron-deficient porphyrin complex Fe(NO)(TFPPBr8) (1; TFPPBr8 = 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) are reported with respect to its electron-transfer behavior. Complex 1 undergoes three 1-electron processes: two reversible redns. and one irreversible oxidn. Spectroelectrochem. measurements (IR and UV/visible/NIR spectroscopy) of 14NO- and 15NO-contg. material indicate that the 1st redn. to 1- occurs largely on the NO ligand to produce nitroxyl anion (NO-) character, as evident from the considerable change in nNO from 1715 to around 1550 cm-1. The 2nd redn. to 12- does not result in a further shift of nNO to lower frequencies, but to a surprising high-energy shift to 1590 cm-1. This and the notable changes of the characteristic porphyrin vibrations as well as significant changes of the UV/visible absorptions indicate a porphyrin-centered process; DFT calcns. predict the shift of nNO to higher frequencies for the intermediate- and high-spin states of 12-. The oxidn. of 1 is irreversible on the voltammetry timescale, but chem. reversible in spectroelectrochem. expts., suggesting that the cationic form dissocs. to the corresponding ferric porphyrin and NO. DFT calcns. support the interpretation of the exptl. results. on SciFinder(R)

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