Analisis spektra UV-Vis
senyawa kompleks
Warna senyawa kompleks
Konfigurasi elektronik atom multi-elektron
Apakah makna konfigurasi 2p2 ?
n = 2; l = 1; ml = -1, 0, +1; ms = ± 1/2
Penataan elektron yang sesuai
microstates
beda energi karena tolakan antar elektron (inter-electronic repulsions)
Konfigurasi elektronik atom multi-elektron  pasangan RS
Russell-Saunders (or LS) coupling
Untuk tiap elektron 2p
n = 2; l = 1
ml = -1, 0, +1
ms = ± 1/2
Untuk tiap atom multi-elektron
L = total orbital angular momentum quantum number
S = total spin angular momentum quantum number
Spin multiplicity = 2S+1
ML = ∑ml (-L,…0,…+L)
MS = ∑ms (S, S-1, …,0,…-S)
• ML/MS menyatakan microstates
• L/S menyatakan states (kumpulan
microstates)
• Group microstates dengan energi yang
sama disebut terms
Menentukan microstates untuk p2
Spin multiplicity = 2S + 1
Menentukan harga L, ML, S, Ms untuk terms yang berbeda
1S
2P
Mengklasifikasikan microstates p2
Largest ML is +2,
so L = 2 (a D term)
and MS = 0 for ML = +2,
2S +1 = 1 (S = 0)
1D
Next largest ML is +1,
so L = 1 (a P term)
and MS = 0, ±1 for ML = +1,
2S +1 = 3
3P
Spin multiplicity = # columns of microstates
One remaining microstate
ML is 0, L = 0 (an S term)
and MS = 0 for ML = 0,
2S +1 = 1
1S
Largest ML is +2,
so L = 2 (a D term)
and MS = 0 for ML = +2,
2S +1 = 1 (S = 0)
1D
Next largest ML is +1,
so L = 1 (a P term)
and MS = 0, ±1 for ML = +1,
2S +1 = 3
3P
ML is 0, L = 0
2S +1 = 1
1S
Energy of terms (Hund’s rules)
Lowest energy (ground term)
Highest spin multiplicity
3P term for p2 case
3P
has S = 1, L = 1
If two states have
the same maximum spin multiplicity
Ground term is that of highest L
before we did:
p2
ML & MS
Microstate
Table
the largest ML L
spin multiplicity = Σcolumns
or 2S+1, S the largest MS
States (S, P, D)
Spin multiplicity
Terms
3P, 1D, 1S
Ground state term
3P
single e- (electronic state)  multi-e- (atomic state)
For metal complexes we need to consider
d1-d10
d2
3F, 3P, 1G, 1D, 1S
For 3 or more electrons, this is a long tedious process
But luckily this has been tabulated before…
Transitions between electronic terms will give rise to spectra
Remember what we’re after ?
Theory to explain electronic
excitations/transitions observed for metal
complexes
Selection rules
(determine intensities)
Laporte rule
g  g forbidden (that is, d-d forbidden)
but g  u allowed (that is, d-p allowed)
Spin rule
Transitions between states of different multiplicities forbidden
Transitions between states of same multiplicities allowed
These rules are relaxed by molecular vibrations, and spin-orbit coupling
Breakdown of selection rules
Group theory analysis of term splitting
Free ion
term for
d2
3F, 3P, 1G, 1D, 1S
Real complexes
Tanabe-Sugano diagrams
• show correlation of
spectroscopic transitions
observed for ideal Oh
complexes with electronic
states
• energy axes are
parameterized in terms of Δo
and the Racah parameter (B)
which measures repulsion
between terms of the same
multiplicity
d2
d2 complex: Electronic transitions and spectra
only 2 of 3 predicted transitions
observed
TS diagrams Other dn configurations
d3
d9
d1
d2
d8
Other configurations
d3
The limit between
high spin and low spin
the spectra of dn hexaaqua complexes of 1st row TMs
The d5 case
All possible transitions forbidden
Very weak signals, faint color
symmetry labels
Charge transfer spectra
Metal character
LMCT
Ligand character
Ligand character
MLCT
Metal character
Much more intense bands
[Cr(NH3)6]3+
Determining Do from spectra
d1
d9
One transition allowed of energy Do
Determining Do from spectra
mixing
mixing
Lowest energy transition = Do
Ground state mixing
E (T1gA2g) - E (T1gT2g) = Do