Analisis spektra UV-Vis senyawa kompleks

Warna senyawa kompleks

Konfigurasi elektronik atom multi-elektronApakah makna konfigurasi 2p2 ?n = 2; l = 1; ml = -1, 0, +1; ms = 1/2microstatesbeda energi karena tolakan antar elektron (inter-electronic repulsions)

Konfigurasi elektronik atom multi-elektron pasangan RS Russell-Saunders (or LS) couplingUntuk tiap elektron 2p n = 2; l = 1ml = -1, 0, +1ms = 1/2Untuk tiap atom multi-elektronL = total orbital angular momentum quantum numberS = total spin angular momentum quantum numberSpin 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 berbeda1S2P

Mengklasifikasikan microstates p2Spin multiplicity = # columns of microstates

Energy of terms (Hunds rules)Lowest energy (ground term)Highest spin multiplicity3P term for p2 caseIf two states havethe same maximum spin multiplicityGround term is that of highest L3P has S = 1, L = 1

before we did:p2the largest ML Lspin multiplicity = columnsor 2S+1, S the largest MS

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

For metal complexes we need to considerd1-d10For 3 or more electrons, this is a long tedious processBut luckily this has been tabulated before

Transitions between electronic terms will give rise to spectra

Remember what were after ?Theory to explain electronic excitations/transitions observed for metal complexes

Selection rules(determine intensities)Laporte ruleg g forbidden (that is, d-d forbidden)but g u allowed (that is, d-p allowed)Spin ruleTransitions between states of different multiplicities forbiddenTransitions between states of same multiplicities allowedThese rules are relaxed by molecular vibrations, and spin-orbit coupling

Consequencies of selection rule

Type of transitionTypical max/dm3mol-1cm-1ExampleSpin-forbidden d-d

Breakdown of selection rules

Group theory analysis of term splitting

Free ion term for d2

Tanabe-Sugano diagramsd2show correlation of spectroscopic transitions observed for ideal Oh complexes with electronic statesenergy axes are parameterized in terms of o and the Racah parameter (B) which measures repulsion between terms of the same multiplicity

Orgel diagramsshows : The information about the number of available terms of the same multiplicity as the multiplicity of the ground state for the case of weak ligand fieldsallow us to assign absorption bands to some certain transitions in the order of their increased energy.

We can also expect blue or red shifts in absorption spectra as the ligand field increases.

TS diagrams Other dn configurations

Other configurationsThe limit betweenhigh spin and low spin

the spectra of dn hexaaqua complexes of 1st row TMs

The d5 caseAll possible transitions forbiddenVery weak signals, faint color

symmetry labels