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

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Chapter 5 5.3.2. Stepwise analysis of the reaction scheme The postulation of the complete reaction mechanism (Scheme 5.1) was based on the following detail: The correct identification of the niobium starting material [NbCl2(OMe)3(MeOH)] was done with 93 Nb NMR. This was discussed in detail in Section 5.2.2. MeO MeO 85 Cl Nb Cl OHMe OMe Figure 5.3: Predicted niobium(V) starting reagent in solution. The formation of the final product is well-defined as indicated by the successful characterisation by means of IR, UV/Vis, X-Ray diffraction, 1 H-, 13 C- and 93 Nb NMR. Figure 5.4: The formation product, [NbCl(acac)(OMe)3], on which the kinetic study is based. Preliminary experiments indicated at least 2 consecutive reaction steps – one fast and one slow reaction, see Figure 5.5. In this experiment, the reaction between [NbCl2(OMe)3(MeOH)] and acacH in MeOH was followed at 25.0 o C. In the initial absorbance vs wavelength scans of [NbCl2(OMe)3 (MeOH)] is indicated in red. When adding acacH to this solution a fast step is observed with peak formation at 323 nm. This is indicated by the red arrow. The second, slower step (blue arrow) involved the disappearance of the peaks at 276 and 323 nm.
Chapter 5 Figure 5.5: Typical UV/Vis spectra of [NbCl2(OMe)3(MeOH)] (5 x 10 -5 M) and [acacH] (5 x 10 -4 M) in MeOH (∆t = 30 min); (a) spectrum of absorbance versus a range of wavelengths, and (b) a graph of absorbance versus time at 323 nm. T = 25.0 °C In order to verify that the observed, fast reaction involves only one reaction step, as opposed to two or more consecutive steps, the preliminary experimental data was fitted to mathematical models representing a one-step pseudo first-order (Eq. 5.1) and a two-consecutive-step pseudo first-order (Eq. 5.2) reaction, respectively (see Figure 5.6): ( ) A =A1- A1-A 0 obs ( ) ( ) 86 -k .t e obs ⎛ ⎞ ⎜ ⎟ ⎝ ⎠ (5.1) ( ) ( ) -k .t -k .t A = A -B e obs1 + B -B e obs2 +B obs 0 0 0 1 1 (5.2) with Aobs = the observed absorbance, A0 and B0 = the initial absorbance for the first and second steps, A1 and B1 = the final absorbance for the first and second steps, respectively, and kobs1/2 = the observed rate constant for each step. (a) (b)
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A solution and solid state study of
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Table of contents Abbreviations and
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3.4 Infrared Spectroscopy (IR) ....
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Abbreviations and Symbols Abbreviat
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Abstract 93 Nb NMR was successfully
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Opsomming 93 Nb KMR is met sukses g
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Chapter 1 metals. 3 Due to Wollasto
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Synopsis... 2. Literature Review of
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Chapter 2 Niobium resembles tantalu
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2.1.2 Uses Chapter 2 Niobium has a
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2.2 Separation of Nb and Ta 2.2.1 M
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Chapter 2 Buachuang et al. 16 repor
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Chapter 2 Niobium oxide surfaces ex
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2.4.6 Water absorption Chapter 2 Th
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Chapter 2 been reported in literatu
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Chapter 2 containing niobium as the
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Chapter 2 conclusions, with regard
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Chapter 2 Figure 2.5: Structure of
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2.6.3.3 [NbCl3O(ttbd) - ] Chapter 2
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Chapter 2 (a) (b) Figure 2.10: Stru
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2.7 Alkoxides Chapter 2 Specific kn
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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
Page 87 and 88: Chapter 4 Table 4.9: Hydrogen bonds
Page 89 and 90: Chapter 4 According to our knowledg
Page 91 and 92: 5.2 Experimental procedures 5.2.1 K
Page 93 and 94: Chapter 5 corresponds to one specie
Page 95: 5.3 Results and Discussion 5.3.1 Pr
Page 99 and 100: 5.3.3 Derivation of the rate law Ch
Page 101 and 102: Chapter 5 The Stopped-flow data (fa
Page 103 and 104: Chapter 5 Figure 5.9: Eyring plot,
Page 105 and 106: Chapter 5 However, more information
Page 107 and 108: Chapter 6 second reaction entailed
Page 109 and 110: 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)-
Page 115 and 116: Appendix A O(7)-C(10)-C(11) 123.6 (
Page 117 and 118: Appendix A H(18E)-C(18B)-H(18F) 109
Page 119 and 120: Appendix A H(18F) 6243 6605 575 75
Page 121 and 122: Appendix A Table 3.3: Bond angles (
Page 123 and 124: Appendix A Table 3.4: Anisotropic d
Page 125: Appendix B Appendix B B 1 Supplemen
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A solution and solid state study of niobium complexes University of ...

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