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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 6
BKCSDE 21(6)
June 20, 2000 

 
Title
In situ Structural Investigation of Iron Phthalocyanine Monolayer Adsorbed on Electrode Surface by X-ray Absorption Fine Structure
Author
Sunghyun Kim, Toshiaki Ohta,Gwanghoon Kwag
Keywords
Abstract
Structural changes of an iron phthalocyanine (FePC) monolayer induced by adsorption and externally applied potential on high area carbon surface have been investigated in situ by iron K-edge X-ray absorption fine structure (XAFS) in 0.5 M H2S04. Fine structures shown in the X-ray absorption near edge structure (XANES) for microcrystalline FePC decreased upon adsorption and further diminished under electrochemical conditions. Fe(II)PC(-2) showed a 1s -> 4p transition as poorly resolved shoulder to the main absorption edge rather than a distinct peak and a weak 1s -> 3d transition. The absorption edge position measured at half maximum was shifted from 7121.8 eV for Fe(lI)PC(-2) to 7124.8 eV for [Fe(III)PC(-2)]+ as well as the 1s -> 3d pre-edge peak being slightly enhanced. However, essentially no absorption edge shift was observed by the 1-electron reduction of Fe(Il)PC(-2), indicating that the species formed is [Fe(II)PC(-3)]-. Structural parameters were obtained by analyzing extended X-ray absorption fine structure (EXAFS) oscillations with theoretical phases and amplitudes calculated from FEFF 6.01 using multiple-scattering theory. When applied to the powder FePC, the average iron-to-phthalocyanine nitrogen distance, d(Fe-Np) and the coordination number were found to be 1.933 Å and 3.2, respectively, and these values are the same, within experimental error, as those reported ( 1.927Å and 4). Virtually no structural changes were found upon adsorption except for the increased Debye-Wailer factor of 0.005Å from 0.003Å2. Oxidation of Fe(II)PC(-2) to [Fe(III)PC(-2)]+ yielded an increased d(Fe-Np) (1 .98Å) and Debye-Wailer factor (0.005Å2). The formation of [Fe(II)PC(-3)]-, however, produced a shorter d(Fe-Np) of 1.91Å the same as that of crystalline FePC within experimental error, and about the same DebyeWaller factor(0.006Å2).
Page
588 - 594
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