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. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Coordination Compounds What is their main characteristic property?

3. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License A clue…

4. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Nearly all coordination compounds are COLOURED

5. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Breathalyzers

6. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Presumptive tests for drugs e.g. the Duquenois test for marijuana

7. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Remember! Coordination compounds are the compounds of the transition metals (d block elements) Why are TM compounds coloured?

8. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License We need to look at the electronic configuration of the transition metals, to answer this question

9. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License [Ar] 4s 2 3d n

10. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License There are 5 d-orbitals d yz d xy d xz dz2dz2 d x 2 y 2 Note change of axis

11. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Energy 1s1s 2s2s 3s3s 2p2p 3p3p 3d3d N = 1 N = 2 N = 3 Each orbital will hold 2 electrons d-orbitals can hold from 1 – 10 electrons

12. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License We get a clue as to how their colour arises, by considering zinc Zn = d 10 (completely FULL d-orbitals)

13. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Zinc (d 10 ) compounds are WHITE (not coloured!) When d-orbitals are FULL there is no colour

14. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License COLOUR must have something to do with partially filled d-orbitals

15. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Crystal Field Theory This theory explains why TM compounds are coloured

16. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Crystal Field theory says… “In the ELEMENT, the d-orbitals are DEGENERATE (of the same energy) Each orbital will hold 2 electrons Energy 3d3d

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” 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. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License How does this help us to explain COLOUR?

19. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Consider the Fe 2+ ion (d 6 ) If this ion makes an octahedral complex, its 6 d-electrons will sit in the split d-orbitals, as shown: Energy

20. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License If we shine light on the Fe 2+ complex…  An electron could absorb enough energy (=  ) to move from the bottom orbitals to the top orbitals: Energy

21. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Note: we haven’t changed the number of PAIRED electrons

22. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License ONE pair of electrons Energy

23. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License When an electron is promoted from a low energy level to a higher energy level, the process is called an ELECTRONIC TRANSITION

24. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License How do electronic transitions make compounds COLOURED?

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. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Electronic Spectrum – Visible light LOW HIGH Energy

27. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Whatever energy is absorbed, the remainder is TRANSMITTED It is the TRANSMITTED light that gives the compound its colour

28. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License For Example  TRANSMITTED LIGHT COLOUR of compound would be a mixture of these ABSORBED LIGHT

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  

30. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License So, why are Zinc compounds white? Because the orbitals are completely filled, there is no room for electronic transitions to take place NO COLOUR (WHITE) Energy

31. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License  What happens if  is so big, that electrons prefer to pair up in the lower level, and not jump up to the higher level?

32. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 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 Energy 

33. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Consider the Fe 2+ octahedral complex, again SMALL  VERY LARGE  Energy  

34. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License How does this affect the COLOUR?

35. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Extended Electronic Spectrum ULTRA VIOLET INFRAR ED 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. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License What other characteristic properties do the TM compounds display?

37. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Look again at the Fe 2+ octahedral complex The MAGNETIC properties of these two Fe 2+ compounds are very different Energy  

38. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License PARAMAGNETIC DIAMAGNETIC Energy  

39. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License This dual magnetic behaviour is another characteristic property of coordination compounds

40. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License SUMMARY

41. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License What you need to know… Two characteristic properties of coordination compounds are: –Colour –Dual magnetic behaviour E.g. Some iron(II) compounds are paramagnetic, whilst others are diamagnetic

42. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Crystal Field Theory In a coordination compound the d-orbitals are not all the same energy Colour arises from electronic transitions within the d- orbitals Dual magnetic behaviour arises due to different values of  There are two reasons for coordination compounds to be white: Electronic transitions cannot occur (e.g. if the d-orbitals are full)  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

43. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Acknowledgements JISC HEA Centre for Educational Research and Development School of natural and applied sciences School of Journalism SirenFM http://tango.freedesktop.org