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3.7.3 Discussion Chapter 3 A limited amount of structural information of niobium(V) mono coordinated to O,O’- bidentate complexes is available. Crystals suitable for X-ray crystallography were obtained for the first three synthesis reactions at -21.0 °C ([NbCl(acac)(OMe) 3], [Nb(acac)(OEt)2(O)]4, [NbCl(phacac)(OMe)3] and [NbCl2(phacac)(OMe)2]). These reactions were also duplicated with an increase in the molar equivalents of ligand added, from two to five, but only the mono coordinated bidentate complexes were formed every time. All of the synthesized crystals decomposed quickly when exposed to air and elevated temperatures above 0 °C . Selected crystals had to be synthesized repeatedly before stable enough samples could be collected for analysis on the X-Ray diffractometer. Subsequently, elemental analysis could not be performed due to the sensitive nature of the products. This was also confirmed by 1 H NMR of the products before and after environmental exposure. The 1 H NMR results for [NbCl(phacac)(OMe)3] and [NbCl2(phacac)(OMe)2] seems confusing at first glance, however two crystal structures were obtained from the same crystal. Hence two different species were observed on the 1 H and 13 C NMR spectrums. This is an extremely rare occurrence and is discussed in more detail in Chapter 4 (Section 4.5). The last three synthesis reactions ([NbCl4(acac)], [NbCl4(hfacac)] and [NbCl(trop)(OMe)3]) either formed powders or crystals that were not suitable for analysis on the X-Ray diffractometer. Several attempts were made to recrystallize the products, but to no avail. 3.7.4 Conclusion Four new niobium(V) complexes containing O,O’-bidentate ligands have been obtained and successfully characterized with IR, as well as 1 H-, 13 C- and 93 Nb NMR. The crystallographic characterisation of these crystals are discussed in detail in the next chapter. 57
4. Crystallographic Synopsis... Characterisation of Niobium(V) β- Diketonato Complexes A detailed discussion on the crystallographic characterisation of three novel crystal structures are given. Specific emphasis is placed on the structural properties of these complexes. 4.1 Introduction ooooooooooooooo In this chapter the solid state characterisation of selected niobium(V) complexes containing O,O’-bidentate ligands is presented. The crystallographic structure determination of (acetylacetonato-κ 2 -O,O’)chloridotrimethoxidoniobium(V) (1), tetrakis(acetylacetonato-κ 2 -O,O’)octakis(etoxy)tetrakis(µ 2 -oxo)tetraniobium(V) (2) and the two structures that were obtained from the same crystal, (1-phenyl-1,3- butanedionato-κ 2 -O,O’)chloridotrimethoxidoniobium(V) and (1-phenyl-1,3-butanedionato-κ 2 -O,O’)dichloridodimethoxidoniobium(V) (3a and 3b) are presented in detail. Positional parameters and all bond distances and angles are given in the supplementary data (Appendix A). 58
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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
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 and 32: Chapter 2 containing niobium as the
Page 33 and 34: Chapter 2 conclusions, with regard
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: 3.7.2.4 Synthesis of [NbCl4(acac)]:
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 and 96: 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
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
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Appendix A H(18F) 6243 6605 575 75
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Appendix A Table 3.3: Bond angles (
Page 123 and 124:
Appendix A Table 3.4: Anisotropic d
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Appendix B Appendix B B 1 Supplemen
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