Chapter 4 - Jacobs University

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<strong>Chapter</strong> 4 16-Iron Metal Center Nanocluster Figure 4.3 Front and side view of the structure of 2 emphasising the FeO 6 octahedra (brown) in polyhedral representation. Colour code: W (green), O (red), P (pink). Polyanion 2 was generated by rather different synthetic procedures with respect to the type of iron precursors and the solvents (Experimental Section). The Bremen group developed three slightly different synthesis procedures for 2 vs. two of the Bielefeld group (the last two 81
<strong>Chapter</strong> 4 16-Iron Metal Center Nanocluster mentioned below). For example, 2 can be prepared by reaction of a solution of P 8 W 48 with (i) FeCl 3 in 0.5 M LiCH 3 COO/CH 3 COOH buffer, pH 4.0 and a few drops of 30% H 2 O 2 , (ii) Fe(ClO 4 ) 3 in 0.5 M LiCH 3 COO/CH 3 COOH buffer, pH 4.0, (iii) FeSO 4 in 0.5 M LiCH 3 COO/CH 3 COOH buffer, pH 4.0 and a few drops of 30% H 2 O 2 , (iv) [Fe 3 O(CH 3 COO) 6 (H 2 O) 3 ]Cl∙H 2 O (Fe 3 Ac 6 ) in 1M NaCH 3 COO/CH 3 COOH buffer, pH 4.2 and (v) FeCl 2 in 1M NaCH 3 COO/CH 3 COOH buffer, pH 4.2 in presence of O 2 . Interestingly, the latter reaction can be considered as a model for the formation of the Fe 3+ oxide nucleus of ferritin. It became apparent that, as expected, the pH is a crucial parameter besides the acetate medium. On the other hand, it is possible to use a large variety of iron salts as educts, ranging from mononuclear Fe 2+ and Fe 3+ complexes (the former requires addition of an oxidant) to trinuclear Fe 3+ carboxylates. These observations support earlier knowledge that POM syntheses in general depend very much on the boundary conditions in the reaction vessel (e.g. pH and solvent). Polyanion 2 exhibits a highly attractive symmetrical D 4h structure (Figures 4.3 and 4.4). The large cavity (roughly 9 Å x 9 Å x 7 Å = 567 Å 3 ) of the “cyclic template/host” P 8 W 48 has been “decorated” with a cationic nanocluster built up by 16 FeO 6 octahedra, resulting in a smaller, central cavity (roughly 6 Å x 6 Å x 5 Å = 180 Å 3 ). The related “Fe 16 ring” is composed of eight pairs of structurally equivalent, edge-shared FeO 6 octahedra which are connected to each other via corners. While most of the Fe-O-Fe bridges are monoprotonated, four are diprotonated (presence of H 2 O ligands). This can be confirmed by looking at the related bond valence sums (BVS) of these oxygen atoms. 12 For example, the protonated oxygens (with the corresponding BVS values) of the polyanion in the mixed lithium-potassium salt 2a are O14F (BVS 0.69), O23F (0.71), O13F (1.08), O24F (1.11), O14G (1.17), O23G (1.27), O1FE (1.31), O2FE (1.32), 82
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Synthesis, Structure and Properties
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"The greatest book of philosophy, w
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system, space group I4/m, unit cell
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Acknowledgements The accomplishment
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teaching, and Professor Maravanji S
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2.1.2 Single crystal X-ray diffract
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5.5 Conclusion…………………
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9.1.6.1 Results and discussion…
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9.3.5 Synthesis of K 12 [Hf 4 (µ 2
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Crespo………………………
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Figure 5.4 ORTEP view of the asymme
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Figure 9.6 31 P NMR of 7a in H 2 O/
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Figure 9.34 TGA spectrum of 17a…
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Figure 9.62 FTIR spectrum of 23a…
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Table 9.6 Crystal data and structur
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Chapter 1 Introduction heteropolyan
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Chapter 7 Pt-containing Polyoxometa
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Chapter 8 Collaborative Work Chapte
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Chapter 8 Collaborative Work 8.2.1
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Chapter 9 Unpublished Results Figur
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Curriculum Vitae SIB SANKAR MAL Dep
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EDUCATION PhD Jacobs University (20
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POSTER, ORAL PRESENTATION 1. Poster
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6. “Two Iron-Containing Tungstoge
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Appendix
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Appendix
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