2.3 Results
3.3.2 EXAFS Fitting
The least-squares EXAFS fit was produced in all three k-weights. Para- meters that were varied during the fit were the edge-shift ΔE0, the amp-
litude reduction factor S2
0, and the mean-square relative displacement of the
scattering path-length, σ2, (also referred to as the ‘Debye-Waller factor’ of
XAFS), presented in Table 3.2.
Inter-atomic distances in the first coordination sphere were fitted to crystallographic data, and are summarised in Table 3.3.
Table 3.2: Results of the first-shell fits of Ru K-edge EXAFS data. Least- squares fit of edge-shift ∆E0, amplitude reduction factor S20, expansion factor α
, and the mean-square relative displacement parameterσ2. Goodness of fit given
by χ2red R-factor. Sample χ2 χ2 red R- ΔE0 S20 α σ2 factor (eV) · 10−2 · 10−2 ˚A2 Ru0 - - - - - 4 104724 32369 0.019 2.8 ±1.7 0.8 ± 0.13 n.a.a 0.3 ±0.1 5 41188 3831 0.033 3.4 ±0.7 0.7 ± 0.07 0.2 ± 0.2 0.5 ±0.08 10 71554 17715 0.014 3.7 ±1.4 0.8 ± 0.05 n.a.a 0.07 b 13 44728 17691 0.016 3.3 ±1.7 0.8 ± 0.06 n.a.a 0.08 b 21 81317 12406 0.019 3.2 ±1.7 0.8 ± 0.05 1.7 ± 0.8 0.4 ±0.6 14 31495 4492 0.027 3.9 ±1.0 0.8 ± 0.09 1.4 ± 0.4 0.17 ± 0.08 22 47533 5756 0.027 3.9 ±1.4 0.8 ± 0.10 n.a.a 0.15 ± 0.08 30 65909 3173 0.037 4.0 ±0.9 1.1 ± 0.08 0.8 ± 0.1 0.3 ±0.09 31 12622 1956 0.010 7.9 ±1.0 0.9 ± 0.08 0.1 ± 0.3 0.5 ±0.1 30∗ 43364 5851 0.019 3.2 ±1.1 0.8 ± 0.08 -0.4 ± 0.4 0.01 ± 0.1 a not applicable, R
S was fitted as RX + ∆R. b fixed value.
∗fitted to X-ray crystallographic data of [10]. χ2 is the goodness-of-fit
parameter, scaled to the estimated uncertainty. χ2red is χ2 divided by the
number of free fit-parameters. R-factor describes the deviation between the fitted and the experimental curve.
Figure 3.6: XAS data for complexes21and30. I) Normalised XAS spectra, II) extracted EXAFS (‘k-space’), III) Fourier Transform (‘R-space’), IV) real part of FT.
the range of Δ R = Rmax − Rmin (Table 3.1) was used for the fit. The
iodido complexes 5, 14 and 22 showed a significant second-shell peak in the FT which was included into the fitting range after successfully fitting the first-shell peak.
Table 3.3 compares the calculated absorber-scatterer distances (RS) to
the crystallographically determined inter atomic distances (RX). The com-
parison between the crystallographic data that were presented in Chapter 2 (Section 2.3.4, p. 72) and the Ru K-edge XAS data obtained here aims to answer the question whether the TSCs are sulfur bound in the solid state.
The data in Table 3.3 show that the bond distances calculated by the EXAFS fit are within±0.05 ˚A of each other and also match the range of the crystallographically determined distances. In particular, the Ru-S distance
Table 3.3: Fit result for interatomic distances (˚A), fitted as separate distances (˚A)
No. X, Y, Z d Ru-N d Ru-S1 d Ru-Cl/I/S2 δ(S1/Cl)
RX N, S, Cl 2.13 2.36 2.43 0.08 10 N, S, Cl 2.08 2.32 2.41 0.09 13 N, S, Cl 2.12 2.35 2.42 0.07 21 N, S, Cl 2.11 2.35 2.41 0.05 14 N, S, I 2.12 2.36 2.73 0.37 22 N, S, I 2.12 2.36 2.73 0.37 30 N, S1, S2 2.11 2.33 2.42 0.09 (RX = 2.1027) (RX = 2.31) (RX = 2.39) -0.08 30* N, S1, S2 2.12 2.33 2.41 0.08
*fitted to X-ray crystallographic data of 10.
is very similar between all mononuclear complexes. The theoretical values are close to the crystallographic standard of 2.3519 ˚A, except for monomer 21. For 21, the fit result of 2.3214 ˚A is closer to the Ru-S distance in the dimer 30 (2.3113 ˚A). The Ru-I distances in complexes 14and 22were fitted via an arbitrary single scattering path of 2.7 ˚A length with a result of 2.7284 ˚A for 14 and 2.7249 ˚A for 22. The last column in Table 3.3 presents the difference between the fitted distance between the Ru-S bond and the Ru-Cl bond.
The EXAFS data of 30were also fitted to the X-ray crystal structure of mononuclear complex 10to show that the geometry is different and the fit result worse than when the correct structure of the dimer is used to build the model. The results show that this is the case. Although a fit with a reasonable R-factor was obtained (see Table 3.2), and the main parameters are refinable to sensible values, the half path-length for the single scattering paths in the first shell differ from the monomer model to a greater extent than from the correct structure.
It is therefore concluded that the bulk material of30is of dimeric nature, because it fits better to the X-ray crystal structure of 30 than that of monomer 10.
Os L3-edge EXAFS of complex [31]
The Os L3-edge XAS data were treated in the same way as the Ru K-
edge data. EXAFS fitting to the crystallographic data for complex 30 was achieved by exchanging the central absorber in the model for Os prior to the prediction of scattering paths with iffeffit.
Figure 3.8 shows the fit result in k-space and R-space, including the fit- ting window. The optimised parameters of the fit are included in Table 3.2. Table 3.4: Fit-results of first-shell EXAFS fit of Os L3-edge XAS of complex31
Path N S2 0 σ2 ∆E0 ΔR Ref f R ·10−3 (eV) ·10−3 ˚A ˚A ˚A N1.1 1 0.913 5.34±1.0 7.9±1.0 2.49± 2.10270 2.10520 C57.1 2 0.913 5.34±1.0 7.9±1.0 2.60± 2.18930 2.19190 C25.1 2 0.913 5.34±1.0 7.9±1.0 2.66± 2.24370 2.24636 C48.1 2 0.913 5.34±1.0 7.9±1.0 2.72± 2.29180 2.29452 S3.1 1 0.913 5.34±1.0 7.9±1.0 2.74± 2.31130 2.31404 S3.2 2 0.913 5.34±1.0 7.9±1.0 2.84± 2.39220 2.39504 C15.2 1 0.913 5.34±1.0 7.9±1.0 3.03± 2.55490 2.55793 C14.1 1 0.913 5.34±1.0 7.9±1.0 3.49± 2.94250 2.94599 C23.1 C25.1 1 0.913 5.34±1.0 7.9±1.0 3.51± 2.96210 2.96562 N2.1 1 0.913 5.34±1.0 7.9±1.0 3.67± 3.09320 3.09687 C56.2 1 0.913 5.34±1.0 7.9±1.0 4.07± 3.42770 3.43177 Os3.1 1 0.913 5.34±1.0 7.9±1.0 4.15± 3.49560 3.49975
Figure 3.7: First-shell EXAFS fit results shown in R-space to compare chlor- ido complex [21] to its iodido analogue [22]. Theoretical model for the fit was produced from X-ray crystallographic data of complex [10].
Figure 3.8: Plots demonstrating the fitting result for Os L3-edge data recorded
for Os(II) complex 31. Fit result is shown in k2-weighted k-space, and in R- spacce. Theoretical model for the fit was produced from X-ray crystallographic data of complex