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
microstatesbeda 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, +1ms = ± 1/2
Untuk tiap atom multi-elektronL = total orbital angular momentum quantum numberS = 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
Spin multiplicity = # columns of microstates
Next largest ML is +1,so L = 1 (a P term)
and MS = 0, ±1 for ML = +1,2S +1 = 3
3P
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
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
If two states havethe same maximum spin multiplicity
Ground term is that of highest L
3P has S = 1, L = 1
before we did:
p2
ML & MS
MicrostateTable
States (S, P, D)Spin multiplicity
Terms3P, 1D, 1S
Ground state term3P
the largest ML Lspin multiplicity = Σcolumnsor 2S+1, S the largest MS
single e- (electronic state) multi-e- (atomic state)
For metal complexes we need to considerd1-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
d2
• 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 complex: Electronic transitions and spectra
only 2 of 3 predicted transitions observed
TS diagrams Other dn configurations
d1 d9
d3
d2 d8
d3
Other configurations
The limit betweenhigh spin and low spin
the spectra of dn hexaaqua complexes of 1st row TMs
The d5 case
All possible transitions forbiddenVery weak signals, faint color
symmetry labels
Charge transfer spectra
LMCT
MLCT
Ligand character
Metal character
Metal character
Ligand character
Much more intense bands
[Cr(NH3)6]3+
Determining o from spectra
d1d9
One transition allowed of energy o
Lowest energy transition = o
mixing
mixing
Determining o from spectra
Ground state mixing
E (T1gA2g) - E (T1gT2g) = o