Analisis spektra UV-Vis senyawa kompleks

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1 Analisis spektra UV-Vis senyawa kompleks

2 Warna senyawa kompleks

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4 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)

5 Russell-Saunders (or LS) coupling
Konfigurasi elektronik atom multi-elektron  pasangan RS Russell-Saunders (or LS) coupling 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) Untuk tiap elektron 2p n = 2; l = 1 ml = -1, 0, +1 ms = ± 1/2 ML/MS menyatakan microstates L/S menyatakan states (kumpulan microstates) Group microstates dengan energi yang sama disebut terms

6 Menentukan microstates untuk p2

7 Spin multiplicity = 2S + 1

8 Menentukan harga L, ML, S, Ms untuk terms yang berbeda
2P

9 One remaining microstate
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 One remaining microstate ML is 0, L = 0 (an S term) and MS = 0 for ML = 0, 2S +1 = 1 1S 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

10 Next largest ML is +1, so L = 1 (a P term) and MS = 0, ±1 for ML = +1, 2S +1 = 3 3P Largest ML is +2, so L = 2 (a D term) and MS = 0 for ML = +2, 2S +1 = 1 (S = 0) 1D ML is 0, L = 0 2S +1 = 1 1S

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12 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

13 before we did: p2 ML & MS Microstate Table States (S, P, D)
the largest ML L spin multiplicity = Σcolumns or 2S+1, S the largest MS Microstate Table States (S, P, D) Spin multiplicity Terms 3P, 1D, 1S Ground state term 3P

14 single e- (electronic state)  multi-e- (atomic state)

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17 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…

18 Transitions between electronic terms will give rise to spectra

19 Remember what we’re after ?
Theory to explain electronic excitations/transitions observed for metal complexes

20 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

21 Breakdown of selection rules

22 Group theory analysis of term splitting

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24 Free ion term for d2 3F, 3P, 1G, 1D, 1S Real complexes

25 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

26 d2 complex: Electronic transitions and spectra
only 2 of 3 predicted transitions observed

27 TS diagrams Other dn configurations

28 Other configurations d3 The limit between high spin and low spin

29 the spectra of dn hexaaqua complexes of 1st row TMs

30 The d5 case All possible transitions forbidden
Very weak signals, faint color

31 symmetry labels

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36 Charge transfer spectra
Metal character LMCT Ligand character Ligand character MLCT Metal character Much more intense bands

37 [Cr(NH3)6]3+

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39 Determining Do from spectra
One transition allowed of energy Do

40 Determining Do from spectra
mixing Lowest energy transition = Do

41 E (T1gA2g) - E (T1gT2g) = Do
Ground state mixing E (T1gA2g) - E (T1gT2g) = Do