CO ligand is higher than CN- ligand in the spectrochemical series
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The stack exchange question title asks why the CO ligand is higher than CN- in the spectrochemical series, but the source text does not establish their relative order.
Ligands which cause a large splitting Δ of the d-orbitals are referred to as strong-field ligands, such as CN− and CO from the spectrochemical series
In inorganic chemistry, crystal field theory (CFT) describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution (anion neighbors). This theory has been used to describe various spectroscopies of transition metal coordination complexes, in particular optical spectra (colors). CFT successfully
the nature of the metal ion.
the metal's oxidation state. A higher oxidation state leads to a larger splitting relative to the spherical field.
the…
Ligands…
# Why is CO ligand higher than CN- in the spectrochemical series?
- Tags: coordination-compounds, molecular-orbital-theory, crystal-field-theory
- Score: 7
- Views: 9,254
- Answers: 1
- Asked by: Tetraquark (115 rep)
- Asked on: Aug 8, 2018
- Last active: Aug 8, 2018
- License: CC BY-SA 4.0
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## Question
I've drawn MO diagrams for both molecules and they are isoelectronic. The main difference is that $\\ce{C}$ is closer in electronegativity to $\\ce{N}$ than it is to $\\ce{O}$ so there will be less stabilisation of the bonding orbitals for $\\ce{CO}$ due to the increased energy difference in the AO's.
Does this difference lead to $\\ce{CO}$ having its $\\pi^\*$ orbital (LUMO) lower than that of $\\ce{CN^{-1}}$ so it more readily accepts $\\pi$ backdonation from a metal centre? Does this alone account for why $\\ce{CO}$ is higher in the spectrochemical series? What about the difference between the $\\sigma$ orbitals (HOMO) in $\\ce{CO}$ and $\\ce{CN^{-1}}$?
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## Accepted Answer — Score: 5
- By: orthocresol (72,999 rep)
- Answered on: Aug 8, 2018
You're on the right track. It has to do with the energies of the frontier orbitals. As you rightly said, both species are isoe
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