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Many ligands are capable of binding metal ions through multiple sites, usually because the ligands have lone pairs on more than one atom. Such ligands are polydentate. [12] Ligands that bind via more than one atom are often termed chelating. A ligand that binds through two sites is classified as bidentate, and three sites as tridentate.
L-type ligands are neutral ligands that donate two electrons to the metal center, regardless of the electron counting method being used. These electrons can come from lone pairs, pi, or sigma donors. [5] [page needed] The bonds formed between these ligands and the metal are dative covalent bonds, which are also
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.
Ligands are ordered alphabetically by name and precede the central atom name. The number of ligands coordinating is indicated by the prefixes di-, tri-, tetra- penta- etc. for simple ligands or bis-, tris-, tetrakis-, etc. for complex ligands. For example:
Where L represents the number of neutral ligands adding two electrons to the metal center (typically lone electron pairs, pi-bonds and sigma bonds. Most encountered ligands will fall under this category. X represents covalent-bonding ligands such as halogen anions.
The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively. [7] The hapticity of a metal-ligand complex, can influence the electron count. [7] Hapticity (η, lowercase Greek eta), describes the number of contiguous ligands coordinated to a metal. [7]
The spectrochemical series is an empirically-derived list of ligands ordered by the size of the splitting Δ that they produce. It can be seen that the low-field ligands are all π-donors (such as I −), the high field ligands are π-acceptors (such as CN − and CO), and ligands such as H 2 O and NH 3, which are neither, are in the middle.
Tetradentate ligands can be neutral so that the charge of the whole complex is the same as the central atom. A tetradentate monoanionic (TMDA) ligand has one donor atom with a negative charge. [8] A tetradentate dianionic ligand has a double negative charge, and tetradentate trianionic ligands have a triple negative charge.