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

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Abstract This research project focused on the investigation and identification of various niobium(V) complexes containing selected O,O’-bidentate ligands that could potentially be used for the selective separation of niobium from tantalum. Emphasis was placed on acetylacetone (acacH) type of ligands due to the ease of varying their electronic and steric properties. The crystallographic characterization of three novel complexes, (acetylacetonato-κ 2 - O,O’)chloridotrimethoxidoniobium(V) (1), the “cage”-like structure of 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) (3a) and (1-phenyl-1,3- butanedionato-κ 2 -O,O’)dichloridodimethoxidoniobium(V) (3b), is discussed and compared to literature. Complex 1 crystallized in an orthorhombic crystal system and space group Pbca, while complexes 2, 3a and 3b all crystallized in a monoclinic crystal system and a space group P21/c, for all. In general it was observed that these mono substituted β-diketonato complexes of niobium(V) crystallized in a distorted octahedral coordination polyhedron. The average O-Nb-O bite angle and Nb-O bond distance for these complexes were determined as 80.5 (1) ° and 2.108 (2) Å, respectively. A kinetic investigation was conducted to follow the formation of the (acetylacetonato- κ 2 -O,O’)chloridotrimethoxidoniobium(V) complex in methanol. The coordination mechanism is postulated for the two observed steps of acacH coordination, of which the initial coordination of the ligand takes place in the first step. The equilibrium constant, K1, was determined as 1975 (201) M -1 at 25.0 °C. The second, rate determining step is representative of the total reaction and includes the ring-closure of the acac ligand and yields K1 as 1403 (379) M -1 . Within experimental error, this value is in good agreement with that of the first step. When comparing the rate constants, k1 and k2, it is found that the first reaction is roughly six orders of magnitude (10 6 ) faster than the slower, second reaction step. VI
Abstract 93 Nb NMR was successfully used in characterising the niobium(V) products synthesised and played an important role in the kinetic study of the project. With regards to the kinetic study; solvent coordination proceeded rapidly upon solvation of the dimeric starting material, [NbCl5]2, in methanol and the niobium(V) starting reagent was correctly determined as [NbCl2(OMe)3(MeOH)] through 93 Nb NMR. VII
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: Abbreviations and Symbols Abbreviat
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 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
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3.5.1 Bragg’s law Chapter 3 Bragg
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3.5.3 ‘Phase problem’ Chapter 3
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Chapter 3 A = ∑ ε cl (3.14) In
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Chapter 3 t1/2 = 54 = . 3.7 Sy
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3.7.2.4 Synthesis of [NbCl4(acac)]:
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4. Crystallographic Synopsis... Cha
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Chapter 4 packages 2 respectively.
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Chapter 4 4.3 Crystal Structure of
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Chapter 4 longer bonds (C1-C2, C2-C
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Chapter 4 Figure 4.5: Packing of [N
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Chapter 4 Figure 4.7: Molecular str
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Chapter 4 Table 4.5: Selected bond
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Chapter 4 Figure 4.11: Molecular st
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Chapter 4 Figure 4.12: The phacac p
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Chapter 4 Table 4.9: Hydrogen bonds
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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
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Chapter 5 Figure 5.5: Typical UV/Vi
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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,
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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 (
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Appendix A A 2 Supplementary Data f
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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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A solution and solid state study of niobium complexes University of ...

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