A solution and solid state study of niobium complexes University of ...

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Chapter 2 metal ions, usually forming a six-membered chelate ring [Fig 2.2]. Acetylacetone is also capable of keto-enol tautomerism; the tautomers exist in equilibrium with each other and structurally they occupy a syn conformation and a cis configuration [Fig 2.1]. 55 Figure 2.2: Metal complexation by an acetylacetonate anion. Although acetylacetonate complexes of many metal ions are well known, relatively few compounds have been reported for niobium, especially in the plus five oxidation state. 56 2.6.1 Tetrakis(β-diketonate) niobium(IV) complexes: 2.6.1.1 [Nb(thd)4] The first niobium(IV) tetrakis β-diketonate complex to be characterized by X- ray crystallography, was published in 1975 by Pinnavaia et al. 57 The aim of the study was to fully characterize the coordination geometry of a tetrakis coordinated tetramethylheptanedionate (thd) complex of niobium. The final 55 D. J. Otway, W. S. Rees Jnr, Coordination Chemistry Reviews, 210, 281, 2000 56 F. H. Allen, Acta Cryst., B58, 380, 2002. 57 T. J. Pinnavaia, B. L. Barnett, G. Podolsky, A. Tulinsky, J. Am. Chem. Soc., 97, 2712, 1975. 21
Chapter 2 conclusions, with regard to the completed characterization, defined the square antiprismatic properties of the coordination sphere. The average Nb-O(thd) bond distance was determined as 2.13 Å. This set the field for niobium β- diketonate research for the future. Comparisons were made with a similar zirconium complex and were found to be not isomorphous. 2.6.1.2 [Nb(hfacac)4] Figure 2.3: Structure of [Nb(thd)4]. In 1998 Calderazzo et al. 58 published a structure for the 4-coordinated 1,1,1,5,5,5-hexafluoroacetylacetonato (hfacac) niobium complex. The study involved characterization by means of X-ray crystallography and an investigation into the electronic structure by means of electron paramagnetic resonance (EPR) spectroscopy. Comparison was made between the two similar compounds of niobium and zirconium (M(hfacac)4, M = Nb, Zr). X-ray crystallography revealed that both compounds had a square antiprismatic coordination at the metal with an average M-O(hfacac) bond distance of 2.12 Å for Nb and 2.18 Å for Zr. The EPR investigation obtained the point of symmetry at the paramagnetic centre for both complexes. 58 F. Calderazzo, U. Englert, C. Maichle-Mossmer, F. Marchetti, G. Pampaloni, D. Petroni, C. Pinzino, J. Strahle, G. Tripepi, Inorg. Chim. Acta., 270, 177, 1998. 22
Page 1 and 2: A solution and solid state study of
Page 3 and 4: Table of contents Abbreviations and
Page 5 and 6: 3.4 Infrared Spectroscopy (IR) ....
Page 7 and 8: Abbreviations and Symbols Abbreviat
Page 9 and 10: Abstract 93 Nb NMR was successfully
Page 11 and 12: Opsomming 93 Nb KMR is met sukses g
Page 13 and 14: Chapter 1 metals. 3 Due to Wollasto
Page 15 and 16: Synopsis... 2. Literature Review of
Page 17 and 18: Chapter 2 Niobium resembles tantalu
Page 19 and 20: 2.1.2 Uses Chapter 2 Niobium has a
Page 21 and 22: 2.2 Separation of Nb and Ta 2.2.1 M
Page 23 and 24: Chapter 2 Buachuang et al. 16 repor
Page 25 and 26: Chapter 2 Niobium oxide surfaces ex
Page 27 and 28: 2.4.6 Water absorption Chapter 2 Th
Page 29 and 30: Chapter 2 been reported in literatu
Page 31: Chapter 2 containing niobium as the
Page 35 and 36: Chapter 2 Figure 2.5: Structure of
Page 37 and 38: 2.6.3.3 [NbCl3O(ttbd) - ] Chapter 2
Page 39 and 40: Chapter 2 (a) (b) Figure 2.10: Stru
Page 41 and 42: 2.7 Alkoxides Chapter 2 Specific kn
Page 43 and 44: Chapter 2 Reactions of dialkylamid
Page 45 and 46: Chapter 2 other NbCl5-x(OMe)x produ
Page 47 and 48: Chapter 2 In 1991 Lee et al. 83 pub
Page 49 and 50: EtO EtO EtO EtO Cl Nb Cl Cl Nb Cl R
Page 51 and 52: Chapter 2 The hemicarbonate formed
Page 53 and 54: Synopsis... 3. Synthesis and Charac
Page 55 and 56: Chapter 3 with γ = magnetogyric ra
Page 57 and 58: Chapter 3 electromagnetic spectrum
Page 59 and 60: 3.5.1 Bragg’s law Chapter 3 Bragg
Page 61 and 62: 3.5.3 ‘Phase problem’ Chapter 3
Page 63 and 64: Chapter 3 A = ∑ ε cl (3.14) In
Page 65 and 66: Chapter 3 t1/2 = 54 = . 3.7 Sy
Page 67 and 68: 3.7.2.4 Synthesis of [NbCl4(acac)]:
Page 69 and 70: 4. Crystallographic Synopsis... Cha
Page 71 and 72: Chapter 4 packages 2 respectively.
Page 73 and 74: Chapter 4 4.3 Crystal Structure of
Page 75 and 76: Chapter 4 longer bonds (C1-C2, C2-C
Page 77 and 78: Chapter 4 Figure 4.5: Packing of [N
Page 79 and 80: Chapter 4 Figure 4.7: Molecular str
Page 81 and 82: Chapter 4 Table 4.5: Selected bond
Page 83 and 84:
Chapter 4 Figure 4.11: Molecular st
Page 85 and 86:
Chapter 4 Figure 4.12: The phacac p
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Chapter 4 Table 4.9: Hydrogen bonds
Page 89 and 90:
Chapter 4 According to our knowledg
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5.2 Experimental procedures 5.2.1 K
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Chapter 5 corresponds to one specie
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5.3 Results and Discussion 5.3.1 Pr
Page 97 and 98:
Chapter 5 Figure 5.5: Typical UV/Vi
Page 99 and 100:
5.3.3 Derivation of the rate law Ch
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Chapter 5 The Stopped-flow data (fa
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Chapter 5 Figure 5.9: Eyring plot,
Page 105 and 106:
Chapter 5 However, more information
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Chapter 6 second reaction entailed
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Appendix A Table 1.3: Bond angles (
Page 111 and 112:
Appendix A A 2 Supplementary Data f
Page 113 and 114:
Appendix A C(16)-H(16B) 0.96 C(16)-
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Appendix A O(7)-C(10)-C(11) 123.6 (
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Appendix A H(18E)-C(18B)-H(18F) 109
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Appendix A H(18F) 6243 6605 575 75
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Appendix A Table 3.3: Bond angles (
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Appendix A Table 3.4: Anisotropic d
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Appendix B Appendix B B 1 Supplemen
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