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In inorganic chemistry, the cis effect is defined as the labilization (or destabilization) of CO ligands that are cis to other ligands. 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.
[16] [17] [18] For example, the CO ligands of octahedral complexes, such as Cr(CO) 6, transform as a 1g, e g, and t 1u, but only the t 1u mode (antisymmetric stretch of the apical carbonyl ligands) is IR-allowed. Thus, only a single ν CO band is observed in the IR spectra of the octahedral metal hexacarbonyls. Spectra for complexes of lower ...
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 ...
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.
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.
σ bonding from electrons in CO's HOMO to metal center d-orbital. π backbonding from electrons in metal center d-orbital to CO's LUMO. The electrons are partially transferred from a d-orbital of the metal to anti-bonding molecular orbitals of CO (and its analogs). This electron-transfer strengthens the metal–C bond and weakens the C–O bond.
Considering both weak and strong ligand fields, a Tanabe–Sugano diagram shows the energy splitting of the spectral terms with the increase of the ligand field strength. It is possible for us to understand how the energy of the different configuration states is distributed at certain ligand strengths.
In inorganic chemistry, the trans effect is the increased lability of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands. . It is attributed to electronic effects and it is most notable in square planar complexes, although it can also be observed for octahedral complexes.