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)

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

Menentukan microstates untuk p2

Spin multiplicity = 2S + 1

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

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

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

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 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

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

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 One transition allowed of energy Do

Determining Do from spectra mixing Lowest energy transition = Do

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