Chemical Structure: Chemical Bonding. Properties of Coordination Compounds

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Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.

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Chemical Structure: Chemical Bonding. Properties of Coordination Compounds

  1. 1. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Properties of Coordination Compounds University of Lincoln presentation
  2. 2. Coordination Compounds What is their main characteristic property? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  3. 3. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License A clue…
  4. 4. Nearly all coordination compounds are COLOURED This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  5. 5. Breathalyzers This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  6. 6. Presumptive tests for drugs This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License e.g. the Duquenois test for marijuana
  7. 7. Remember! Coordination compounds are the compounds of the transition metals (d block elements) Why are TM compounds coloured? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  8. 8. We need to look at the electronic configuration of the transition metals, to answer this question This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  9. 9. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License [Ar] 4s 2 3d n Sc Ti V Cr Mn Fe Co Ni Cu Zn d 1 d 2 d 3 d 4 d 5 d 6 d 7 d 8 d 9 d 10 H Be Li Na K Rb Cs Fr Mg Ca Sr Ba Ra Sc Y La Ac Ti V Cr Mn Fe Co Ni Cu Zn Zr Hf Ta W Re Os Ir Pt Au Hg Tl Nb Mo Tc Ru Rh Pd Ag Cd In Sn Pb Bi Po At Rn Xe Kr Ar Ne Sb Te I Ga Al Ge Si P S Cl As Se Br Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr He B C N O F Lanthanoids Actinoids
  10. 10. There are 5 d-orbitals This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License d yz d xy d xz d z 2 d x 2 y 2 Note change of axis
  11. 11. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Energy 1 s 2 s 3 s 2 p 3 p 3 d N = 1 N = 2 N = 3 Each orbital will hold 2 electrons d-orbitals can hold from 1 – 10 electrons
  12. 12. We get a clue as to how their colour arises, by considering zinc Zn = d 10 (completely FULL d-orbitals) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  13. 13. Zinc (d 10 ) compounds are WHITE (not coloured!) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License When d-orbitals are FULL there is no colour
  14. 14. COLOUR must have something to do with partially filled d-orbitals This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  15. 15. Crystal Field Theory This theory explains why TM compounds are coloured This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  16. 16. Crystal Field theory says… This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License “ In the ELEMENT, the d-orbitals are DEGENERATE (of the same energy) Each orbital will hold 2 electrons Energy 3 d
  17. 17. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License … But, in a COORDINATION COMPOUND, NOT all of the orbitals have the same energy” For example, in an octahedral coordination compound, the d-orbitals are split as follows: Energy 
  18. 18. How does this help us to explain COLOUR ? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  19. 19. Consider the Fe 2+ ion (d 6 ) <ul><li>If this ion makes an octahedral complex, its 6 d-electrons will sit in the split d-orbitals, as shown: </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Energy
  20. 20. If we shine light on the Fe 2+ complex… <ul><li>An electron could absorb enough energy (=  ) to move from the bottom orbitals to the top orbitals: </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Energy Energy
  21. 21. Note: we haven’t changed the number of PAIRED electrons This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  22. 22. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License ONE pair of electrons ONE pair of electrons Energy Energy
  23. 23. When an electron is promoted from a low energy level to a higher energy level, the process is called an ELECTRONIC TRANSITION This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  24. 24. How do electronic transitions make compounds COLOURED ? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  25. 25. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License If the electron is going to jump from the lower level to the higher level, it has to ABSORB energy from visible light It needs to absorb an amount of energy =  Energy 
  26. 26. Electronic Spectrum – Visible light This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License LOW HIGH Energy
  27. 27. Whatever energy is absorbed, the remainder is TRANSMITTED It is the TRANSMITTED light that gives the compound its colour This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  28. 28. For Example This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License  TRANSMITTED LIGHT COLOUR of compound would be a mixture of these ABSORBED LIGHT
  29. 29. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License  is large High energy is needed to promote electron: Blue end is absorbed Red end is transmitted  is small Low energy is needed to promote electron: Red end is absorbed Blue end is transmitted Energy   Energy
  30. 30. So, why are Zinc compounds white? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Because the orbitals are completely filled, there is no room for electronic transitions to take place NO COLOUR (WHITE) Energy
  31. 31. What happens if  is so big, that electrons prefer to pair up in the lower level, and not jump up to the higher level? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  32. 32. <ul><li>There comes a point, when  is so big, that it is easier for electrons to pair up in the lower level, rather than staying unpaired, by jumping up to the higher level </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Energy 
  33. 33. Consider the Fe 2+ octahedral complex, again This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License SMALL  VERY LARGE  Energy   Energy
  34. 34. How does this affect the COLOUR ? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  35. 35. Extended Electronic Spectrum This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License ULTRA VIOLET INFRARED When  is very large, the amount of energy required to promote an electron from the lower to the higher level is outside the visible range – hence the compound will appear WHITE 
  36. 36. What other characteristic properties do the TM compounds display? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  37. 37. Look again at the Fe 2+ octahedral complex This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License The MAGNETIC properties of these two Fe 2+ compounds are very different Energy   Energy
  38. 38. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License PARAMAGNETIC DIAMAGNETIC Energy   Energy
  39. 39. This dual magnetic behaviour is another characteristic property of coordination compounds This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  40. 40. SUMMARY This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  41. 41. What you need to know… <ul><li>Two characteristic properties of coordination compounds are: </li></ul><ul><ul><li>Colour </li></ul></ul><ul><ul><li>Dual magnetic behaviour </li></ul></ul><ul><ul><ul><li>E.g. Some iron(II) compounds are paramagnetic, whilst others are diamagnetic </li></ul></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  42. 42. Crystal Field Theory <ul><li>In a coordination compound the d-orbitals are not all the same energy </li></ul><ul><li>Colour arises from electronic transitions within the d-orbitals </li></ul><ul><li>Dual magnetic behaviour arises due to different values of  </li></ul><ul><li>There are two reasons for coordination compounds to be white: </li></ul><ul><ul><ul><li>Electronic transitions cannot occur (e.g. if the d-orbitals are full) </li></ul></ul></ul><ul><ul><ul><li> is so large that the absorbed energy in an electronic transition is in the UV region and not the visible region of the electronic spectrum </li></ul></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  43. 43. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Acknowledgements <ul><li>JISC </li></ul><ul><li>HEA </li></ul><ul><li>Centre for Educational Research and Development </li></ul><ul><li>School of natural and applied sciences </li></ul><ul><li>School of Journalism </li></ul><ul><li>SirenFM </li></ul><ul><li>http://tango.freedesktop.org </li></ul>

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