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The Tolman electronic parameter (TEP) is a measure of the electron donating or withdrawing ability of a ligand. It is determined by measuring the frequency of the A 1 C-O vibrational mode (ν(CO)) of a (pseudo)-C 3v symmetric complex, [LNi(CO) 3 ] by infrared spectroscopy , where L is the ligand of interest.
CO is a well-known strong pi-accepting ligand in organometallic chemistry that will labilize in the cis position when adjacent to ligands due to steric and electronic effects. The system most often studied for the cis effect is an octahedral complex M(CO) 5 X where X is the ligand that will labilize a CO ligand cis to it.
Substitution in 17-electron complexes, which are rare, proceeds via associative mechanisms with a 19-electron intermediates. M(CO) n + L → M(CO) n L M(CO) n L → M(CO) n−1 L + CO. The rate of substitution in 18-electron complexes is sometimes catalysed by catalytic amounts of oxidants, via electron transfer. [52]
As depicted in the molecular orbital diagram above, the computed electronic structure contains a purely ligand-based orbital with a 2u symmetry. [1] Invoking this ligand-only orbital allows for satisfaction of the 18-electron rule in M(CO) 8 complexes, and is stabilized by the field effect of the metal on the ligand cage. [14]
That is, the unoccupied d orbitals of transition metals participate in bonding, which influences the colors they absorb in solution. In ligand field theory, the various d orbitals are affected differently when surrounded by a field of neighboring ligands and are raised or lowered in energy based on the strength of their interaction with the ...
In cases where the ligand has low energy LUMO, such orbitals also participate in the bonding. The metal–ligand bond can be further stabilised by a formal donation of electron density back to the ligand in a process known as back-bonding. In this case a filled, central-atom-based orbital donates density into the LUMO of the (coordinated) ligand.
The total reaction may be diffusion controlled (the electron transfer step is faster than diffusion, every encounter leads to reaction) or activation controlled (the "equilibrium of association" is reached, the electron transfer step is slow, the separation of the successor complex is fast). The ligand shells around A and D are retained.
Inner sphere electron transfer (IS ET) or bonded electron transfer [1] is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants. In inner sphere electron transfer, a ligand bridges the two metal redox centers during the electron transfer event. Inner ...