XANES Analysis of Phthalocyanine Molecular Conductor

Abstract

The dicyano(phthalocyaninato)iron molecular conductor shows the Giant Magnetoresistance (GMR) effect. In order to investigate the effect of the molecular structure and charge on the X-ray absorption in the Fe(Pc)(CN)2 molecule, we measured the Fe K-edge X-ray Absorption Near Edge Structure (XANES) spectra in the TPP[Fe(Pc)L2]2 (L=CN, Br, and Cl), DMDP[Fe(Pc)(CN)2], and [(n-C7H15)4N][Fe(Pc)(CN)2]. In 7134-7152 eV, we found the clear difference in the XANES spectra between these Fe(Pc)(CN)2 compounds. Our multiple scattering calculations indicate that the local structure of the iron and CN ligand, which tends to be changed by the nominal charge in the Pc ring, causes the spectral change.

Ligand and Charge Dependence for Absorption Edge in XANES Spectra of TPP[Fe(Pc)L2]2 Systems

“…The cluster radius is 10 Å as displayed in Fig. 1 (b) and the cluster includes 369 atoms in the present study, while 61 atoms in the previous study [10]. The calculated result is improved especially near the absorption edge compared with the previous study.…”

“…The spectrum calculated on the basis of the cluster structure model, which is made by crystal structure [8], reproduces the experimental result well. Figure 3 (a) shows the comparison between the experimental result and the calculated results in the present and the previous studies [10] in TPP[Fe(Pc)(CN) 2 ] 2 . Here, we apply the density functional theory (DFT) calculation to the cluster models which are constructed by the crystal structures in the reference [8,9] and perform multiple scattering calculations.…”

“…However, other experimental results such as g-value and the magnetization imply that the charge of Fe does not change [9]. The XANES spectra calculated in our previous report [10] do not have the accuracy enough to discuss the contribution of the variation of Fe charge and the ligand field to absorption edge shift. In this paper, we improve the accuracy in the calculation of the electronic structure and multiple scattering.…”

“…The calculation procedure of the XANES spectra based on real space full multiple scattering theory proposed by Fujikawa et al [1][2][3][4][5] is same as the previous report [10]. Here we introduce the theory briefly.…”

“…We have previously reported the analysis of Fe K-edge XANES spectra for TPP[Fe(Pc)L 2 ] 2 systems [10]. In the previous paper, only one Fe(Pc)L 2 molecule, whose size is about 6 Å, is taken into account in the calculation of XANES spectra in various ligands.…”