marvellous metals nyholm lecture 2002 professor tony baker & dr linda xiao faculty of science,...

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

The Royal Australian Chemical Institute (RACI) www.chem.unsw.edu.au/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 MnO4- + 6 H+ + 5 H2O2

2 Mn2+ + 8 H2O + 5 O2

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 V2O5).

• 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 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+

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.

Other redox processes

The rusting of ironBatteriesElectrolysis to purify metalsUsing reductants to liberate

metals from ores

Photoreduction: Blueprint

• Blueprints (an early form of copying) were first made around 1840

2 [Fe(C2O4)3]3- 2 Fe2+ + 2 CO2 + 5 C2O4

2-

(K+ +) Fe2+ + [Fe(CN)6]3- Prussian Blue

• The pigment Prussian Blue has been known since 1704

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+ (max 700nm).

Probable formula: Fe(III)4[Fe(II)(CN)6]3.15H2O

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

levelsX-ray: inner shell electronsUV-Vis: outer shell electronsIR: molecular vibrationsMicrowave: rotations

Vanadium check-up

VO2+ yellow

VO2+ blue

V3+ green

V2+ violet

Emission Spectra

EmissionhνE2E1

Flame tests

LithiumSodium PotassiumCalciumStrontiumBariumCopper

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

AbsorptionhνE2E1

Absorption: demonstration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

500 550 600 650 700 750 800 850

Wavelength (nm)

Absorbance

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

LightsourceFlameDetector

hνE2E1 hνE2E1

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

AAS: application

• AAS was long considered the best technique for trace metal analysis.

• Detection Limits (ppb):Cd 1Cr 3Cu 2Pb 10V 20

Vanadium: one more time

VO2+ yellow

VO2+ blue

V3+ green

V2+ 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

OHHNaOHH+

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.

OH2NiOH2OH2OH2H2OH2O2+

Shapes of Complexes

6-coordinate: Octahedral

4-coordinate: Tetrahedral

Demonstration:[Co(H2O)6]2+ + 4 Cl-

[CoCl4]2- + 6 H2O

Changing shapes: demo

[Co(H2O)6]2+ + 4 Cl- [CoCl4]2- + 6 H2O

pink blueOH2CoOH2OH2OH2OH2OH2ClCoClClCl2-2+OCTAHEDRALTETRAHEDRAL

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).

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)

Nickel(II) Complexes: Demo

[Ni(H2O)6]2+ green

[Ni(NH3)6]2+ blue

[Ni(NH2CH2CH2NH2)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.

egt2go

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.

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.

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.

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 O2(g) Al2O3(s) -1676

Fe2O3(s) 2 Fe(s) + 3/2 O2(g) 824

2Al(s) + Fe2O3(s) Al2O3(s)+ 2Fe(s)

-852