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Marvellous Metals

Marvellous Metals. Nyholm Lecture 2002 Professor Tony Baker & Dr Linda Xiao Faculty of Science, UTS. Sir Ronald Nyholm 1917-1971. Coordination Chemist Inspiring Chemical Educator Leader of the Profession. Sponsorship.

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Marvellous Metals

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  1. Marvellous Metals • Nyholm Lecture 2002 • Professor Tony Baker & • Dr Linda Xiao • Faculty of Science, UTS

  2. Sir Ronald Nyholm 1917-1971 • Coordination Chemist • Inspiring Chemical Educator • Leader of the Profession

  3. Sponsorship • The Royal Australian Chemical Institute (RACI) www.chem.unsw.edu.au/raci • Crown Scientific • APS

  4. Marvellous Metals: the Lecture • Redox Chemistry • Spectra and Spectroscopy • Coordination Chemistry

  5. Redox Chemistry • Many reactions can be classified as redox reactions. • These are reactions in which the oxidation numbers of the elements involved change

  6. Example: Redox Chemistry • An acidified solution of permanganate ions reacts with hydrogen peroxide to give dioxygen gas: • 2 MnO4- + 6 H+ + 5 H2O2 • 2Mn2+ + 8 H2O + 5 O2 • Mn +7  +2; O (in peroxide) –1  0

  7. Vanadium • Vanadium is a transition element that displays a maximum oxidation state of +5 (eg in the oxide V2O5). • Named after Vanadis, the Norse goddess of beauty because of the beautiful colours in solution • Used in high strength steels

  8. Vanadium reduction: demo • Initial: solid NH4VO3 • Acidification: • VO3- + 2 H+ VO2+ + H2O • Reduction (Zn as reductant): • VO2+ + 2 H+ + e- VO2+ + H2O • VO2+ + 2 H+ + e- V3+ + H2O • V3+ + e- V2+

  9. Vanadium Application • Sulfuric Acid Manufacture: • SO2 (g) + ½ O2 (g) SO3 (g) • Vanadium(V) oxide catalysts are used in this process. • Sulfuric acid: 150 million tonnes produced each year.

  10. Other redox processes • The rusting of iron • Batteries • Electrolysis to purify metals • Using reductants to liberate metals from ores

  11. Photoreduction: Blueprint • Blueprints (an early form of copying) were first made around 1840 • 2 [Fe(C2O4)3]3- 2 Fe2+ + 2 CO2 + 5 C2O42- • (K+ +) Fe2+ + [Fe(CN)6]3- Prussian Blue • The pigment Prussian Blue has been known since 1704

  12. More on Prussian Blue • Fe3+ + [Fe(CN)6]4- Prussian Blue • Fe2+ + [Fe(CN)6]3- Turnbull’s Blue • Found to have same spectra / XRD. • Colour arises from charge transfer: • Fe3+ + e  Fe2+ (lmax 700nm). • Probable formula: Fe(III)4[Fe(II)(CN)6]3.15H2O

  13. Spectra and Spectroscopy • Spectrum: solar spectrum, rainbow • Plot of radiation intensity vs. wavelength / frequency • May be absorption or emission

  14. Uses of Spectroscopy • Identification • Quantification • Study bonding / energy levels • X-ray: inner shell electrons • UV-Vis: outer shell electrons • IR: molecular vibrations • Microwave: rotations

  15. Vanadium check-up • VO2+ yellow • VO2+ blue • V3+ green • V2+ violet

  16. Emission Spectra

  17. Flame tests • Lithium • Sodium • Potassium • Calcium • Strontium • Barium • Copper

  18. Flame tests • The thermal energy is enough to shift electrons to higher energy levels (excited state). • The electron returns to a lower energy level with emission of visible radiation.

  19. Absorption spectra

  20. Absorption: demonstration

  21. Absorption and colour • The copper solution appears blue and absorbs red light. • Under white light illumination some wavelengths are absorbed and some are reflected / transmitted. • The object / solution has the complementary colour to the radiation absorbed.

  22. Atomic absorption • Atoms in the ground state will absorb radiation that promotes electrons to an excited state. • The amount of radiation absorbed is proportional to the the number of atoms present. • This concept is the basis of Atomic Absorption Spectroscopy (AAS).

  23. AAS: schematic diagram

  24. AAS: Australia’s contribution • Alan Walsh had worked on emission spectra and molecular spectroscopy. • Demonstrated possibility of AAS in early 1952. • Developed commercially by CSIRO and Australian instrument manufacturers

  25. AAS: application • AAS was long considered the best technique for trace metal analysis. • Detection Limits (ppb): • Cd 1 • Cr 3 • Cu 2 • Pb 10 • V 20

  26. Vanadium: one more time • VO2+ yellow • VO2+ blue • V3+ green • V2+ violet

  27. Coordination Chemistry • ….it is correct to say that modern inorganic chemistry is, especially in solution, the study of complex compounds. • Nyholm, The Renaissance of Inorganic Chemistry, 1956

  28. Dissolution of a salt • Water binds to ions at edges of lattice • When bonds to water are stronger than bonds to ions, the ion enters solution

  29. Examples • Nickel(II) ions in solution: Ni2+(aq). • Species in solution is [Ni(H2O)6]2+. • Other examples would include [Cu(H2O)6]2+, [Fe(H2O)6]3+, etc.

  30. Shapes of Complexes • 6-coordinate: Octahedral • 4-coordinate: Tetrahedral • Demonstration: • [Co(H2O)6]2+ + 4 Cl- • [CoCl4]2- + 6 H2O

  31. Changing shapes: demo • [Co(H2O)6]2+ + 4 Cl- [CoCl4]2- + 6 H2O • pink blue

  32. Coordinate Bond • Many molecules and ions have lone pairs of electrons (eg NH3) and can act as electron pair donors (Lewis bases). • Transition metal ions can have vacant orbitals and can accept electron pairs (Lewis acids).

  33. Ligands • The molecules or ions that bind to a metal ion are known as ligands. • Many ligands are known ranging from monoatomic ions such as chloride to huge protein molecules. • Examples include NH3, H2O, NH2CH2CH2NH2 (diaminoethane, a chelating ligand), SCN- (thiocyanate)

  34. Nickel(II) Complexes: Demo • [Ni(H2O)6]2+ green • [Ni(NH3)6]2+ blue • [Ni(NH2CH2CH2NH2)3]2+ blue-purple • [Ni(dmg)2] red

  35. Colours of Metals Complexes • In an octahedral complex, the d orbitals are split into two energy levels separated by a gap Do. • The size of Do depends on the nature of the ligand.

  36. Differing interactions • Different metals react in different ways with the same ligand. • One example is the difference in interaction of Ni2+ and Co2+ with SCN-. • In the case of cobalt a stable complex ion is formed [Co(SCN)4]2- which is soluble in some organic solvents.

  37. Demonstration • A mixture of Ni2+ and Co2+ is treated with excess SCN-. • 2-Butanone (CH3COCH2CH3) is used to extract the reaction mixture. • Nickel ions remain in the aqueous phase and cobalt ions (as [Co(SCN)4]2-) are extracted into the organic phase.

  38. Application • Many extractive metallurgical processes depend on different metals interacting in different ways with ligands. • Copper can be purified through a solvent extraction technique. • Treatment of 107 tonnes per year of low grade tailings (1%) recovers a further 105 tonnes of copper.

  39. Thermite: Return to Redox • The thermite reaction can be used for such applications as welding in remote locations and depends on the activity of aluminium. • Aluminium powder and iron oxide are mixed together and the reaction is started with burning Mg ribbon. • Highly exothermic reaction!

  40. Thermite Thermodynamics

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