Transition Metals

• Transition metals have partially filled d orbitals.
• Transition metal properties:

  • Multiple oxidation states
  • Form coloured ions in solution
  • Great catalysts
  • Form complexes with ligands
• Ligand Definition

  A molecule that forms a dative bond with a transition metal (donates a pair of electrons to the central metal ion).
• Transition Metal definition

  A metal that can form one or more stable ions with an incomplete d sub-shell.
• Complex ion

  An ion with ligands attached to it.
• Coordination number 


  The number of dative bonds between a metal ion and its ligands.
• Monodentate ligands:

  • Ammonia (:NH3)
  • Chlorine (:Cl-)
  • Hydroxide ions (:OH-)
  • Cyanide ions (:CN-)
  • Water (H2O:)
• Why is water monodentate despite having two lone pairs?

  Both lone pairs occur on the same O atom so due to repulsion and rotation of the molecule so it's impossible for them to form two dative bonds.
• Bidentate ligands:

  • 1,2diaminoethane (H2N(CH2)2NH2)
  • ethanedioate ion ((COO)2)-
• The Chelate Effect


  Multidentate ligands will almost always replace monodentate ligands at a metal centre.

  This is because the substitution increases the amount of moles present in the reaction, increasing entropy and bringing Gibbs free energy change below 0.
• Multidentate ligands:

  EDTA-

  
• Shapes of complex ions:

  • L - linear
  • O - octahedral
  • S - square planar
  • T - tetrahedral
• Six Coordinate Bonds shape:

  Octahedral (90° and 90°)
• Four Coordinate Bonds shape:

  No charge = Square Planar (90°)

  Charge = Tetrahedral (109.5°)
• Two Coordinate Bonds shape:

  Linear (180°)
• Square planar complexes exhibit E-Z isomerism.
• Octahedral complexes exhibit E-Z isomerism with monodentate ligands and Optical isomerism with bidentate ligands.
• In octahedral complexes, optical isomerism occurs when 3 bidentate ligands are attached to the central metal ion. A pair of enantiomers are formed.
• Octahedral complexes with 4 ligands of one type and 2 of another exhibit E-Z isomerism.
• Cisplatin formula

  [PtCl2(NH3)2]
• Cisplatin anti-cancer activity:

  • only Z-isomer
  • Cl ligands replaced by H2O after entering cell due to low intracellular Cl conc.
  • Aquated complex forms links between DNA bases in tumour cell, halting replication and stopping tumour growth.
• Cons of Cisplatin:

  • Only helps bladder/lung cancer
  • Expensive
  • Many side effects: prevents normal cell production, hair loss, immune suppression, kidney damage, infection risk, death.
• 3d orbitals usually have the same energy, when a ligand bonds, some orbitals are given more energy and the 3d orbital is split into different energy levels
• Electrons occupy the lower orbitals (ground state) first.
• If an electron absorbs energy equal to the energy gap, it can jump to the higher orbitals (excited state). This energy is gained from visible light.
• $E =$$hv =$$hc / λ$
• • Visible lights hits ion, some frequencies are absorbed as electron jumps (these depend on the energy gap).
  • Rest of frequencies reflected and combine to make the complement of the colour absorbed.
  • In a coloured complex, the d sub-shell must be PARTIALLY filled.
  • No d electrons/subshell filled = colourless/white compound
• Factors affecting colour:

  • Changes in oxidation state
  • Changes in coordination number
  • Changes in ligand
• Colorimetry definition

  A measurement of colour intensity.
• Spectrometry definition

  A method of measuring how much light a solution absorbs in order to determine concentration.
• Spectrometry method:

  1. White light shone through a filter. Only lets wavelengths through that will be absorbed by solution.
  2. Light passes through sample to colorimeter that shows amount of light absorbed.
  3. Higher concentration of solution = more light absorbed.
• What should the axes be for a calibration curve?


  Y = relative absorbance

  X = concentration of ion
• Benefits of colorimetry:

  • easy to collect a lot of reading
  • concs can be calculated quickly
  • works well at low concs (wont use up substance, wont interfere with any reactions)
• When monodentate ligands are swapped with ones of similar size, coordination number and shape don't change.
• Discuss the role of iron as a heterogeneous catalyst in the Haber process.

  • Heterogenous catalyst - in a different state from the reactants, speeds up reaction by providing alternate pathway with lower activation energy
  • Hydrogen/Nitrogen adsorb onto surface of the iron, reaction takes place, products desorb from irons' surface
  • Large surface area (mesh/powder) increases efficiency, catalyst poisoning can cause active sites to become blocked, lowering life expectancy