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

Sir Ronald Nyholm Coordination Chemist Inspiring Chemical Educator Leader of the Profession

Sponsorship The Royal Australian Chemical Institute (RACI) Crown Scientific APS

Marvellous Metals: the Lecture Redox Chemistry Spectra and Spectroscopy Coordination Chemistry

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

Example: Redox Chemistry An acidified solution of permanganate ions reacts with hydrogen peroxide to give dioxygen gas: 2 MnO H H 2 O 2  2 Mn H 2 O + 5 O 2 Mn +7  +2; O (in peroxide) –1  0

Vanadium Vanadium is a transition element that displays a maximum oxidation state of +5 (eg in the oxide V 2 O 5 ). Named after Vanadis, the Norse goddess of beauty because of the beautiful colours in solution Used in high strength steels

Vanadium reduction: demo Initial: solid NH 4 VO 3 Acidification: VO H +  VO H 2 O Reduction (Zn as reductant): VO H + + e -  VO 2+ + H 2 O VO H + + e -  V 3+ + H 2 O V 3+ + e -  V 2+

Vanadium Application Sulfuric Acid Manufacture: SO 2 (g) + ½ O 2 (g)  SO 3 (g) Vanadium(V) oxide catalysts are used in this process. Sulfuric acid: 150 million tonnes produced each year.

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

Photoreduction: Blueprint Blueprints (an early form of copying) were first made around [Fe(C 2 O 4 ) 3 ] 3-  2 Fe CO C 2 O 4 2- (K + +) Fe 2+ + [Fe(CN) 6 ] 3-  Prussian Blue The pigment Prussian Blue has been known since 1704

More on Prussian Blue Fe 3+ + [Fe(CN) 6 ] 4-  Prussian Blue Fe 2+ + [Fe(CN) 6 ] 3-  Turnbull’s Blue Found to have same spectra / XRD. Colour arises from charge transfer: Fe 3+ + e  Fe 2+ ( max 700nm). Probable formula: Fe(III) 4 [Fe(II)(CN) 6 ] 3.15H 2 O

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

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

Vanadium check-up VO 2 + yellow VO 2+ blue V 3+ green V 2+ violet

Emission Spectra

Flame tests Lithium Sodium Potassium Calcium Strontium Barium Copper

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.

Absorption spectra

Absorption: demonstration

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.

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).

AAS: schematic diagram

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

AAS: application AAS was long considered the best technique for trace metal analysis. Detection Limits (ppb): Cd1 Cr3 Cu 2 Pb 10 V20

Vanadium: one more time VO 2 + yellow VO 2+ blue V 3+ green V 2+ violet

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

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

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

Shapes of Complexes 6-coordinate: Octahedral 4-coordinate: Tetrahedral Demonstration: [Co(H 2 O) 6 ] Cl -  [CoCl 4 ] H 2 O

Changing shapes: demo [Co(H 2 O) 6 ] Cl -  [CoCl 4 ] H 2 O pink blue

Coordinate Bond Many molecules and ions have lone pairs of electrons (eg NH 3 ) and can act as electron pair donors (Lewis bases). Transition metal ions can have vacant orbitals and can accept electron pairs (Lewis acids).

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 NH 3, H 2 O, NH 2 CH 2 CH 2 NH 2 (diaminoethane, a chelating ligand), SCN - (thiocyanate)

Nickel(II) Complexes: Demo [Ni(H 2 O) 6 ] 2+ green [Ni(NH 3 ) 6 ] 2+ blue [Ni(NH 2 CH 2 CH 2 NH 2 ) 3 ] 2+ blue-purple [Ni(dmg) 2 ]red

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

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

Demonstration A mixture of Ni 2+ and Co 2+ is treated with excess SCN -. 2-Butanone (CH 3 COCH 2 CH 3 ) 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.

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 10 7 tonnes per year of low grade tailings (1%) recovers a further 10 5 tonnes of copper.

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!

Thermite Thermodynamics Reaction  H (kJ mol -1 ) 2 Al (s) + 3/2 O 2(g)  Al 2 O 3(s) Fe 2 O 3(s)  2 Fe (s) + 3/2 O 2(g) 824 2Al (s) + Fe 2 O 3(s)  Al 2 O 3(s) + 2Fe (s) -852