The Electronic Spctra of Coordination Compounds配合物的电子光谱

3d Multi-electron Complexes
For complexes with more than one electron in the 3d (and 4s) orbitals of the metal, electron interactions must be considered. The electrons are not independent of each other, and the orbital angular momenta (ml values) and the spin angular momenta (ms values) interact.
Constructing a Microstate Table
ml = +1 Configurations: ___ ___ ___ 0 ___ ___ ___ -1 microstate: ___ (1+,0+) ___ (0+,-1+) ___ (1+,-1+)
These are examples of some of the ground state microstates. Others would have the electrons (arrows) pointing down.
Consider a Cr(III) complex such as [Cr(NH3)6]3+. The ground state configuration is: ____ ____ A transition from the dz2 dx2-y2 dxy to the dz2, or the dyz or dxz to the dx2-y2 ____ ____ ____ orbitals involve a major dxy dyz dxz change in environment.
The interaction is called Russel-Saunders or L-S coupling. The interactions produce atomic states called microstates that are described by a new set of quantum numbers. ML = total orbital angular momentum =Σml MS = total spin angular momentum = Σms
General Observations
d1, d4, d6 and d9 usually have 1 absorption, though a side “hump” results from Jahn-Teller distortions.
General Observations
d2, d3, d7 and d8 usually have 3 absorptions, one is often obscured by a charge transfer band.
The Electronic Spectra of Coordination Compounds
The UV/Vis spectra of transition metal complexes shows the transitions of the electrons. Analysis of these spectra can be quite complex.
4d and 5d Metal Complexes
The lower transition metals undergo further coupling (called j-j coupling or spin-orbit coupling).
3d Multi-electron Complexes
Energy States
Microstates would have the same energy only if repulsion between electrons is negligible. In an octahedral or tetrahedral complex, microstates that correspond to different relative spatial distributions of the electrons will have different energies. As a result, distinguishable energy levels, called terms are seen.
Qualitative Explanation
The transition from the dxz orbitals to the dz2 orbitals involves a relatively minor change in the electronic environment.
Qualitative Explanation
Determining the Energy States of an Atom
A microstate table that contains all possible combinations of ml and ms is constructed. Each microstate represents a possible electron configuration. Both ground state and excited states are considered.
Microstate Table for
2 p
For the carbon atom, ML will range from +2 down to -2, and MS can have values of +1 (both electrons “pointing up”), 0 (one electron “up”, one electron “down”), or -1 (both electrons “pointing down”).
Qualitative Explanation
The transition from orbitals in the xy plane to the dz2 orbitals involves a fairly major change in the electronic environment.
Energy States
To obtain all of the terms for a given electron configuration, a microstate table is constructed. The table is a grid of all possible electronic arrangements. It lists all of the possible values of spin and orbital orientation. It includes both ground and excited states, and must obey the Pauli Exclusion Principle.
Constructing a Microstate Table
Consider an atom of carbon. Its highest occupied orbital has a p2 electron configuration. Microstates correspond to the various possible occupation of the px, py and pz orbitals.
General Observations
d5 complexes consist of very weak, relatively sharp transitions which are spin-forbidden, and have a very low intensity.
Qualitative Explanation
Constructing a Microstate Table
ml = +1 Configurations: ___ ___ ___ 0 ___ ___ ___ -1 microstate: ___ (1+,1-) ___ (0+,0-) ___ (-1+,-1-)
These are examples of some of the excited state microstates.
Microstate Table for
MS ML +2: +1: 0: -1: -2: 1+0+ -1+1+ -1+0+ +1 0 1+11+01-0+ -1+10+0-1-1+ -1+0-1-0+ -1+-11-0-1-1-1-0-1
2 p
The table includes all possible microstates.
Obtaining ∆o
For a d1 configuration, only a single peak is seen. It results from the electron promotion from the t2g orbitals to the eg orbitals. The “toothed” appearance of the peak is due to a Jahn-Teller distortion of the excited state. The energy of the peak = ∆o.
Consider a Cr(III) complex such as [Cr(NH3)6]3+. The ground state configuration is: ____ ____ A transition from the dz2 dx2-y2 dxy to the dx2-y2, or the dyz or dxz to the dz2 ____ ____ ____ orbitals involve a relatively dxy dyz dxz minor change in environment.