Synthesis and Structural Characterization of ... - Jacobs University

Chapter 4
Unpublished Results
Figure 4.5. Side view of ball-and-stick representation of the Fe 16 cluster emphasizing the
coordination of the four lanthanide ions. The color code is as follows: Fe (yellow); Ln (blue);
H 2 O (pink); O (red).
Bond valence sum (BVS) calculations for 24 and 25 are consistent with all tungsten atoms
being in the +6 oxidation state, and all lanthanide and iron ions being in the +3 oxidation
state. 16 In addition, 23 mono- and nine di-protonated oxygen atoms were identified in Fe 16 oxo
cluster (see Figure 4.3). The ranges of BVS for mono- and di-protonated oxygen atoms are
respectively 1.02 – 1.28 and 0.40 – 0.56. The six terminal oxygens of Fe1, Fe2, Fe15 and
Fe16 are diprotonated and correspond to terminal water molecules (pink color in Figure 4.3).
Furthermore, 20 of the 28 bridging Fe–O–Fe oxygens are monoprotonated (gray color in
Figure 4.3). This leaves eight other bridging oxo atoms. The six bridging Fe3–Fe5, Fe4–Fe6,
Fe7–Fe9, Fe8–Fe10, Fe11–Fe13 and Fe12–Fe14 (turquoise color in Figure 4.3) show a BVS
range of 0.59 – 0.67, which is between mono- and diprotonation and led us to believe that we
are looking at three water and three hydroxo ligand disordered over these six sites. This type
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