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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.
Structure of [Co(salen)] 2 O 2. [11]. Salcomine, the cobalt(II) complex of salen ligand is the first synthetic O 2 carrier. [12] Solvated derivatives of the solid complex bind 0.5 equivalent of O 2: 2 Co(salen) + O 2 → [Co(salen)] 2 O 2. Reversible electron transfer reactions are observed in some dinuclear O 2 complexes. [13]
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 greater stabilization that results from metal-to-ligand bonding is caused by the donation of negative charge away from the metal ion, towards the ligands. This allows the metal to accept the σ bonds more easily. The combination of ligand-to-metal σ-bonding and metal-to-ligand π-bonding is a synergic effect, as each enhances the other.
A spectrochemical series is a list of ligands ordered by ligand "strength", and a list of metal ions based on oxidation number, group and element.For a metal ion, the ligands modify the difference in energy Δ between the d orbitals, called the ligand-field splitting parameter in ligand field theory, or the crystal-field splitting parameter in crystal field theory.
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]
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.