http://lawrencekok.blogs pot.com Prepared by Lawrence Kok Video Tutorial on UV /visible spectroscopy, transition metals complexes and splitting of 3d orbitals.
Jun 23, 2015
http://lawrencekok.blogspot.com
Prepared by Lawrence Kok
Video Tutorial on UV /visible spectroscopy, transition metals complexes and splitting of 3d orbitals.
UV and Visible Spectroscopy
• Spectroscopy – interaction of matter with radiation
• Visible Spectroscopy – electronic transition of valence electrons to higher energy level by absorbing radiation in visible range
• UV Spectroscopy – electronic transition of valence electrons to higher energy level by absorbing radiation in UV range
UV and Visible Spectroscopy
Energy difference bet 2p and 3s is HIGHAbsorb UV range - Colourless
Energy difference bet split 3d is SMALLAbsorb Visible range - Coloured
Pic taken from: http://www.extension.org/pages/13116/electromagnetic-spectrum
UV and Visible Spectroscopy
Pic taken from:http://www.hunancreative.com/24.html
Transition metal complexes are coloured – due to splitting of 3d orbitals
* Metal ion surrounded by ligands
1
* 3d orbitals are degenerate without any ligands
2
Transition metal complexes are coloured – due to splitting of 3d orbitals
* Metal ion surrounded by ligands
1
* 3d orbitals are degenerate without any ligands
2
3d orbitals split by ligands
3Splitting
Explanation how splitting occurs due to electron repulsion
Explanation how splitting occurs due to electron repulsion
Splitting of 3d orbitals by ligands – allow electronic transition from lower to higher state
Colour formation due to splitting of 3d orbitals by ligands
Ti 3+ transmit blue/violet region BUT absorb green/orange/red
Ti 3+ violet due to absorption of green/yellow region to excite electrons to higher orbital level
Cu 2+ transmit blue/violet region BUT absorb green/orange/red
Cu 2+ blue due to absorption of green/yellow to excite electrons to higher level
Transition metal have different colours due to• splitting of 3d orbitals• presence of ligands which causes splitting• partially filled 3d orbitals
CuSO4 (anhydrous) without ligands - Colourless
Why some are colourless ?
Cu 2+ anhydrous – colourlessCu 1+ hydrous – colourlessZn 2+ hydrous – colourlessSc 3+ hydrous – colourlessCu 2+ hydrous - colour
Zn 2+ ion with ligand water - Colourless
Sc 3+ ion with ligand water - Colourless
Cu 2+ ion with ligand water – Colour Blue
Cu 1+ ion with ligand water - Colourless
Factors affecting colour of transition metal complexes are• 1. Nature of element• 2. Oxidation state• 3. Type of ligands• 4. Stereochemistry/shape
Elements - Fe2+, Mn2+ , Cu2+ , Co2+
Oxidation state ion - Fe3+ , Fe2+
Factors affecting colour of transition metal complexes are
Different ligands – H20, NH3 , CI-
Stereochemistry – octahedral , tetrahedral
Factor 3. Different ligands – different level of splitting – different colour
Ligands CI- H2O NH3
Ligands F- H2O NH3
Absorption of UV by organic molecules and chromophores
Absorption of UV radiation by C=C, C=O, N=N, N=O gps
UV Electronic transition Chromophores gps
Pic taken from: http://pubs.rsc.org/en/Content/ArticleLanding/2008/NJ/b809055f
Difference bet UV and Visible absorption by
• Coloured - Absorption in visible range• Splitting of 3d is small – falls in visible range
Transition metals Organic molecules/chromophores
• Colourless - Absorption in UV range• Electronic transition from bonding to antibonding orbital (involving pi or lone pair electron)
Pic taken from:http://www.lycocard.com/index.php/lyco_pub/health/
Absorption of UV by organic molecules and chromophores
More conjugation – more delocalization – absorption in visible range - coloured
Absorption of UV by organic molecules and chromophores
More conjugation – splitting energy less – wavelength absorption increase (visible range)
Summary
Absorption of UV by organic molecules and chromophores
• Organic molecules with extensive conjugated double bonds will be coloured• Absorb in visible range
Azo dyesFood dyes
Sun block
ß carotene
Indicators
Absorption of UV by organic molecules and chromophores
How Phenolphthalein indicator changes colour ?
Acidic Colourless
AlkalinePink
Reason for change of colour• change in conjugation• change in delocalization
Acknowledgements
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Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/
Prepared by Lawrence Kok
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