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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.
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:
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.
For example, ferrocene, [(η 5-C 5 H 5) 2 Fe], has two cyclopentadienyl ligands giving a hapticity of 5, where all five carbon atoms of the C 5 H 5 ligand bond equally and contribute one electron to the iron center. Ligands that bind non-contiguous atoms are denoted the Greek letter kappa, κ. [7] Chelating κ2-acetate is an example.
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.
T. Tetraacetylethane; Tetradentate ligand; Transition metal acyl complexes; Transition metal arene complex; Transition metal azide complex; Transition metal carboxylate complex
Ferrocene has two η 5 cyclopentadienyl ligands while Uranocene has two η 8 cyclooctatetraene ligands; however, by covalent bond classification the complexes are found to be ML 4 X 2 and ML 6 X 4. [4] This corresponds to LBN values of 6 and 10 respectively, even though the total coordination numbers would be 10 and 16.
Many metal carbonyl clusters contain ligands aside from CO. For example, the CO ligand can be replaced with myriad alternatives such as phosphines, isocyanides, alkenes, hydride, etc. Some carbonyl clusters contain two or more metals. Others contain carbon vertices. One example is the methylidyne-tricobalt cluster [Co 3 (CH)(CO) 9]. [3]