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This ligand–metal–ligand geometric parameter is used to classify chelating ligands, including those in organometallic complexes. It is most often discussed in terms of catalysis , as changes in bite angle can affect not just the activity and selectivity of a catalytic reaction but even allow alternative reaction pathways to become accessible.
Ethylenediamine ligand chelating to a metal with two bonds Cu 2+ complexes with nonchelating methylamine (left) and chelating ethylenediamine (right) ligands. The chelate effect is the greater affinity of chelating ligands for a metal ion than that of similar nonchelating (monodentate) ligands for the same metal.
Most commonly, amino acids coordinate to metal ions as N,O bidentate ligands, utilizing the amino group and the carboxylate. They are "L-X" ligands. A five-membered chelate ring is formed. The chelate ring is only slightly ruffled at the sp 3-hybridized carbon and nitrogen centers.
The chelate effect increases as the number of chelate rings increases. For example, the complex [Ni(dien) 2)] 2+ is more stable than the complex [Ni(en) 3)] 2+; both complexes are octahedral with six nitrogen atoms around the nickel ion, but dien (diethylenetriamine, 1,4,7-triazaheptane) is a tridentate ligand and en is bidentate. The number of ...
The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac) 3 and M(acac) 2. Mixed-ligand complexes, e.g. VO(acac) 2, are also numerous.
Some are useful commercially, but the topic has attracted regular scholarly scrutiny. Oxalate (C 2 O 4 2-) is a kind of dicarboxylate ligand. [1] As a small, symmetrical dinegative ion, oxalate commonly forms five-membered MO 2 C 2 chelate rings. Mixed ligand complexes are known, e.g., [Co(C 2 O 4)(NH 3) 4] κ+. [2]
DOTA is derived from the macrocycle known as cyclen.The four secondary amine groups are modified by replacement of the N-H centers with N-CH 2 CO 2 H groups. The resulting aminopolycarboxylic acid, upon ionization of the carboxylic acid groups, is a high affinity chelating agent for di- and trivalent cations.
The iminodiacetate dianion is a tridentate ligand, forming metal complexes by forming two, fused, five membered chelate rings. [1] The proton on the nitrogen atom can be replaced by a carbon atom of a polymer to create an ion-exchange resin, such as chelex 100. Complexes of IDA and EDTA were introduced in the early 1950s by Schwarzenbach. [2]