Post on 06-Jul-2018
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Electronic Spectra of Complexes
Color is due to electronic transition b/w levels whose SPACING corresponds tothe wavelength of light available in visible region (complimentary color isobserved).
SPACING depends on:- geometry of complex- nature of ligands- oxidation state of metal
[Co(H2O)6]2+
Oh, Pink[CoCl4]
2-
T d, Blue
[Ni(H2O)6]2+
Oh, Green [Ni(NH3)6]
2+
Oh, Blue
[Cr(H2O)6]2+
Oh, Bright Blue[Cr(H2O)6]
3+
Oh, Violet
Many TM complexes show color, e.g.
3 NH
e
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Electronic Spectra: Examples
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Electronic Spectra
MO diagram of octahedralcomplex discussed so faris based on one-electronmodel
Configuration dn → add effect of e–e repulsion → add effect of Ligand Field
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Effect of e-e repulsion: Term Symbols
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Splitting of Terms in Chemical Environment
(Transformation matrix) (General Transformation matrix)
(else 2l + 1)
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Construction of Correlation Diagram
Configuration dn → add effect of e–e repulsion → add effect of Ligand Field
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Correlation Diagram for a d2 system in Oh
(a) Free ion terms
(b) Weak field terms(c) Strong field ground
and excited configuration
(d) Strong field terms
(e) Intermediate field
Total degeneracy
= (2l+1)*(2s+1)
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Splitting of d n and d 10-n Terms in O h and T d Field
d n vs d 10-n
O h vs T d
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Correlation Diagram for a d2 and d8 system
Octahedral d8 and
tetrahedral d2 on Left Octahedral d2 and
tetrahedral d8 on Right
Ot
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Correlation Diagram for a d4 system
Octahedral d10-n and tetrahedral dn on Left
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Correlation Diagram for a dn system
(a) d2 and d8 (b) d3 and d7 (c) d4 and d6 (d) d5
Octahedral d10-n and tetrahedral dn on Left
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Interpretation of Electronic Spectrum
Selection Rules:Laporte allowed transition are those with a change in parity
Spin allowed transition have same spin multiplicity
Interpretation of Electronic Spectrum:1. No. (and position) of spectral lines2. Intensity of spectral lines
3. Width of spectral band
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Molar absorptivities for various types of electronic transition
observed in complexes
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Ground & excited terms having the same spin for weak field
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Orgel Diagram
d3 system Co2+ ion
Td (right), Oh (left)
T b S Di
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Tanabe – Sugano Diagrams
T b S Di
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Tanabe – Sugano Diagrams
I f F T b S Di
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Info. From Tanabe – Sugano Diagrams d6 system
e.g. Low spin [Co(en)3]+
I f F T b S Di
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Info. From Tanabe – Sugano Diagrams
Ratio = 1.32;
corresponds to D/B = 32.8
Gives B = 657/cm and D = 21550/cm
I f f T b S Di
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Info. from Tanabe – Sugano Diagrams
d3