Inter valence charge transfer
Encyclopedia
In chemistry, intervalence charge transfer, often abbreviated IVCT or even IT, is an electron transfer (thermal or photoinduced) between two metal sites differing only in oxidation state. Quite often such electron transfer reverses the oxidation states of the sites. The term is frequently extended to the case of metal-to-metal charge transfer between non-equivalent metal centres.
Typically, such a process produces a characteristic absorption in the electromagnetic spectrum
of the compound involved. The phenomenon is most often observed in mixed-valence bi- and polymetallic coordination complexes. The IVCT band is usually observed in the visible or near infrared
region of the spectrum and is broad.
The process can be described as follows:
where L is a ligand
.
Typically, such a process produces a characteristic absorption in the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
of the compound involved. The phenomenon is most often observed in mixed-valence bi- and polymetallic coordination complexes. The IVCT band is usually observed in the visible or near infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
region of the spectrum and is broad.
The process can be described as follows:
- LnM+-bridge-M'Ln + hν → LnM-bridge-M'+Ln
where L is a ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
.
Mixed valency and the IT band
Since the energy states of valence tautomers affect the IVCT band, the strength of electronic interaction between the sites, known as α (the mixing coefficient), can be determined by analysis of the IVCT band. Depending on the value of α, mixed valence complexes are classified into three groups:- class I: α ~ 0, the complex has no interaction between redox sites. No IVCT band is observed.
- class II: 0 < α < 0.707, intermediate interaction between sites. An IVCT band is observed.
- class III: α > 0.707, interaction between redox sites is very strong. It is better to consider these sites as one united site, not as two isolated sites.