Lecture_4_OpticalMag

Lecture_4_OpticalMag - Chem 310 Lecture Module 4 Visible/UV...

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Chem 310 Lecture Module 4 Visible/UV Spectra and Magnetism Optical and Magnetic Properties of TM Complexes
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UV/Visible Spectroscopy Complexes give rise to colorful solutions because of d-d transitions which are usually in the visible region of the spectrum due to the magnitude of Δ o . Color can also be due to metal-ligand charge transfer transitions, that arise when ectrons on predominantl metal ased MO’s are e cited to MO’s that are electrons on predominantly metal-based MO’s are excited to MO’s that are predominantly ligand-based (ie., KMnO 4 which is deep purple). Another type of transition is the ligand-to-metal charge transfer transition (similar to above, but reversed). These types of transitions also give rise to the colours of many inorganic minerals (ie Cu 2+ based such as malachite, turquoise, lapis lazuli, etc) . e see the complementary color when visible light of any wavelength is absorbed We see the complementary color when visible light of any wavelength is absorbed. In the Figure above, complementary colors are situated on opposite sides.
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UV/visible spectra for some chromium complexes Shift in energy of the three bands is due to changes in the ligand field strength Ligand field splitting can be measured spectroscopically! The fact that Cr 3+ is d 3 and that there are 3 bands is coincidence! a) [Cr(en) 3 ] 3+ ; b) [Cr(ox) 3 ] 3- ; c) [CrF 6 ] 3- . υ 1 = Δ o . (roughly)
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S Æ A 1g Splitting of energy terms due to correlation effects: Overall degeneracy conserved P Æ T 1g D Æ E g + T 2g F Æ A 2g + T 1g + T 2g E T T Spin multiplicity same as for parent term (ie, doublet ground state splits into two doublet terms G Æ A 1g + E g + T 1g + T 2g Note that electron and hole configurations are the inverse of each other - so a d 1 electron configuration is the inverse of a d 9 electron (d 1 hole configuration) and both will have the same ground state free ion term ( 2 D) - however energy order for the two split levels in d 9 metal ion is inverse of the d 1 case - hole formalism applies to all d n configurations round state terms identical for d 2 d 8 d 3 d 7 but energy terms inverse ground state terms identical for d = d ; d = d ; but energy terms inverse d 1 splitting d 2 splitting Ground-terms arising from d 1 (left) and d 2 (right).
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Splitting of energy terms due to correlation effects: Inverse relationship exists between octahedral and tetrahedral symmetries - a free ion term split into same new terms by tet and oct fields, but energy ordering will be opposite -drop “u” and “g” designation for tet. Symmetry - also note that d n and d 10-n ground state terms the same, but energy splitting is inverse portant:
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This note was uploaded on 02/28/2011 for the course CHEM 310 taught by Professor Nazar during the Fall '09 term at Waterloo.

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Lecture_4_OpticalMag - Chem 310 Lecture Module 4 Visible/UV...

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