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

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Chapter 1 The proposed aims for the study can be briefly summarized as follows: 1. The synthesis of niobium(V) complexes by coordinating it to different O,O’- bidentate ligands. Two ligands are proposed, exploring symmetric and non- symmetric coordination modes: a 3 OH O Figure 1.1: Proposed O,O’-bidentate ligands for the study; (a) acetylacetone (acacH) and (b) 1-phenyl-1,3-butanedione (phacacH). 2. The characterization of new niobium complexes by utilizing their solid state and solution properties. Specific emphasis will be placed on X-Ray Crystallography as well as Infrared-, Ultraviolet/Visible- and Nuclear Magnetic Resonance Spectroscopy. 3. Determination of the nature of the niobium halido starting reagent, as solvent coordination proceeds rapidly in alcohol solutions to form the corresponding alkoxides. Different alkoxide species may form and it is essential to know which take part in the reaction, especially when studying the detailed reaction mechanism by time revealed spectroscopic kinetic studies. 93 Nb NMR will be used to identify the relevant species. 4. A mechanistic investigation of the formation of [NbCl(acac)(OMe)3]. 5. Analysis of results and comparison with the corresponding tantalum study 5 . 5 R. Koen, M.Sc Thesis, University of the Free State, 2012. b
Synopsis... 2. Literature Review of Niobium Background information on the occurrence, properties and chemistry of niobium is briefly discussed. A more detailed review on the coordination of niobium to acetylacetone and its derivatives is also included. 2.1 Introduction ooooooooooooooo Niobium and tantalum are always found associated with each other in their minerals and niobium is 10 to 12 times more abundant in the earth’s crust than tantalum. It never occurs as the free metal and is usually combined with oxygen and other metals forming a niobate. Most niobium deposits occur as carbonatites (carbon- silicate rocks). 1 Primary niobium containing minerals can be divided into two groups; the tantalo- and titano-niobates. Tantalo-niobates consist of tantalic and niobic acid salts. The general formula for this group is (Fe,Mn)M2O6 (M = Nb, Ta) and the mineral is known as niobate or tantalite, depending on which metal dominates. 2 These minerals consist of isomorphic mixtures of the four possible salts and generally contain tin, tungsten, titanium and other impurities. Titano-niobates comprise of the salts of niobic and titanic acids. The most important mineral in this group is pyrochlore. The main sources of pyrochlore are from Brazil and Canada and the general formula for the mineral varies depending on the source. The general formula for a typical Brazilian pyrochlore is (Na,Ca)2M2O6 (M = Nb, Ti) and for that of a Canadian one is (Ba, Ca)2M2O6 (M = Nb, Ti, Ce). 3 1 C. W. Balke, Ind. Eng. Chem., 27, 1166, 1935. 2 N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Butterworths/Heinemann, Oxford, 977, 1997. 3 G. L. Miller, Metallurgy of the Rarer Metals, Butterworths Scientific Publications, London, 6, 548, 1959. 4
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: Chapter 1 metals. 3 Due to Wollasto
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
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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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