Search results
Results From The WOW.Com Content Network
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.
The magnitude of Δ o is determined by the field-strength of the ligand: strong field ligands, by definition, increase Δ o more than weak field ligands. Ligands can now be sorted according to the magnitude of Δ o (see the table below). This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.
As described above, π-donor ligands lead to a small Δ O and are called weak- or low-field ligands, whereas π-acceptor ligands lead to a large value of Δ O and are called strong- or high-field ligands. Ligands that are neither π-donor nor π-acceptor give a value of Δ O somewhere in-between.
Some ligands always produce a small value of Δ, while others always give a large splitting. The reasons behind this can be explained by ligand field theory. The spectrochemical series is an empirically-derived list of ligands ordered by the size of the splitting Δ that they produce (small Δ to large Δ; see also this table):
Strong-field ligands, such as CN − and CO, increase the Δ splitting and are more likely to be low-spin. Weak-field ligands, such as I − and Br − cause a smaller Δ splitting and are more likely to be high-spin. Some octahedral complexes exhibit spin crossover, where the high and low spin states exist in dynamic equilibrium.
T. Tetraacetylethane; Tetradentate ligand; Transition metal acyl complexes; Transition metal arene complex; Transition metal azide complex; Transition metal carboxylate complex
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.
Common functional groups such as ketones usually are only weak ligands and thus often are poor DGs. This problem is solved by the use of a transient directing group. Transient DGs reversibly convert weak DGs (e.g., ketones) into strong DG's (e.g., imines) via a Schiff base condensation. Subsequent to serving their role as DGs, the imine can ...