The Carter–Goddard–Malrieu–Trinquier model (better known as CGMT model) is a model in
inorganic chemistry
Inorganic chemistry deals with chemical synthesis, synthesis and behavior of inorganic compound, inorganic and organometallic chemistry, organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subj ...
, used for the description and prediction of distortions in multiple bonding systems of
main group elements.
Theory
The model predicts that if the double bond is homolytically cleaved in a system R
1 R
2 M = MR
3 R
4, the two
carbene
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a Valence (chemistry), valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms.
Th ...
analog fragments resulting therefrom can subsequently be present in both a
singlet and a
triplet state.
Independently, however, the basic state of the fragments may be a triplet or a singlet state. EA Carter and WA Goddard III showed that the binding energy E
G results from the
bond dissociation energy
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical ...
E
int minus the sum of the singlet-triplet excitation energies ΣΔE S → T of the resulting fragments. E
GBE = E
int - ΣΔE
S → T.
This model was extended by G. Trinquier and J. P. Malrieu by the possibility to make statements about the geometry (characterized by the distance between the metal centers r, and the tilt angle θ) of a double bond system due to ΣΔE
S → T. As can be seen in the illustration, a coplanar structure (θ = 0 °) is optimal for triplet fragments. For singlet fragments, however, there is a double donor-acceptor bond with an angle of θ close to 45 °.
References
Inorganic chemistry
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