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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/10/10 18:56:31」(JST)

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Atom with

monodentate ligands

Denticity refers to the number of atoms in a single ligand that bind to a central atom in a coordination complex.^[1]^[2] In many cases, only one atom in the ligand binds to the metal, so the denticity equals one, and the ligand is said to be monodentate (sometimes called unidentate). Ligands with more than one bonded atom are called polydentate or multidentate. The word denticity is derived from dentis, the Latin word for tooth. The ligand is thought of as biting the metal at one or more linkage points. The denticity of a ligand is described with the Greek letter κ ('kappa').^[3] For example, κ⁶-EDTA describes an EDTA ligand that coordinates through 6 non-contiguous atoms.

Denticity is different than hapticity because hapticity refers exclusively to ligands where the coordinating atoms are contiguous. In these cases the η ('eta') notation is used.^[4] Bridging ligands use the μ ('mu') notation.^[5]^[6]

Classes of denticity[edit]

Polydentate ligands are chelating agents^[7] and classified by their denticity. Some atoms cannot form the maximum possible number of bonds a ligand could make. In that case one or more binding sites of the ligand are unused. Such sites can be used to form a bond with another chemical species.

Bidentate (also called didentate) ligands bind with two atoms, an example being ethylenediamine.

Structure of the pharmaceutical Oxaliplatin, which features two different bidentate ligands.

Tridentate ligands bind with three atoms, an example being terpyridine. Tridentate ligands usually bind via two kinds of connectivity, called "mer" and "fac." Cyclic tridentate ligands such as TACN and 9-ane-S3 bind in a facial manner.
Tetradentate ligands bind with four atoms, an example being triethylenetetramine (abbreviated trien). Tetradentate ligands bind via three connectivities depending on their topology and the geometry of the metal center. For octahedral metals, the linear tetradentate trien can bind via three geometries. Tripodal tetradentate ligands, e.g. tris(2-aminoethyl)amine, are more constrained, and on octahedra leave two cis sites. Many naturally occurring macrocyclic ligands are tetradentative, an example being the porphyrin in heme.
Pentadentate ligands bind with five atoms, an example being ethylenediaminetriacetic acid.
Hexadentate ligands bind with six atoms, an example being EDTA (although it can bind in a tetradentate manner).
Ligands of denticity greater than 6 are well known. The ligands 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) and diethylene triamine pentaacetate (DTPA) are octadentate. They are particularly useful for binding lanthanide ions, which typically have coordination numbers greater than 6.

Relationship between "linear" bi-, tri- and tetradentate ligands (red) bound to an octahedral metal center. The structures marked with * are chiral owing to the backbone of the tetradentate ligand.

Stability constants[edit]

In general, the stability of a metal complex correlates with the denticity of the ligands. The stability of a complex is represented quantitatively in the form of Stability constants. Hexadentate ligands tend to bind metal ions more strongly than ligands of lower denticity.

External links[edit]

EDTA chelation lecture notes. 2.4MB PDF - Slide 3 on denticity

References[edit]

^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "denticity".
^ von Zelewsky, A. "Stereochemistry of Coordination Compounds" John Wiley: Chichester, 1995. ISBN 047195599.
^ http://goldbook.iupac.org/K03366.html
^ http://goldbook.iupac.org/H01881.html
^ http://goldbook.iupac.org/B00741.html>
^ http://goldbook.iupac.org/M03659.html
^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "chelation".

English Journal

Tailoring Ligand Environment toward Development of Colorimetric and Fluorescence Indicator for Biological Mn(II) Imaging.

Adhikari S1, Ghosh A1, Sahana A1, Guria S1, Das D2.
Analytical chemistry.Anal Chem.2016 Jan 19;88(2):1106-10. doi: 10.1021/acs.analchem.5b03551. Epub 2015 Dec 22.
Mn(2+) ion plays an essential role in all forms of life. Paramagnetic nature of Mn(2+) and its close resemblance with Ca(2+) and Mg(2+) are two key limiting factors responsible for the least development of fluorescence probes suitable for bioimaging. In literature we have found only a few Mn(2+) sel
PMID 26654446

Phenolate based metallomacrocyclic xanthate complexes of Co(II)/Cu(II) and their exclusive deployment in [2 : 2] binuclear N,O-Schiff base macrocycle formation and in vitro anticancer studies.

Singh VK1, Kadu R1, Roy H2, Raghavaiah P3, Mobin SM4.
Dalton transactions (Cambridge, England : 2003).Dalton Trans.2016 Jan 19;45(4):1443-54. doi: 10.1039/c5dt03407h.
Potassium salts of phenolate based polydentate xanthate ligands 4,4'-bis(2-dithiocarbonatobenzylideneamino)diphenyl ether () and 4,4'-bis(2-dithiocarbonatonaphthylmethylideneamino)diphenyl ether () have been synthesized and characterized, prior to use. The reaction of or with M(OAc)2 in Et3N affords
PMID 26674056

Distinction between coordination and phosphine ligand oxidation: interactions of di- and triphosphines with Pn(3+) (Pn = P, As, Sb, Bi).

Chitnis SS1, Vos KA1, Burford N1, McDonald R2, Ferguson MJ2.
Chemical communications (Cambridge, England).Chem Commun (Camb).2015 Dec 24;52(4):685-8. doi: 10.1039/c5cc08086j.
Reactions of polydentate phosphines with sources of Pn(3+) (Pn = P, As, Sb, Bi) yield complexes of Pn(1+) (Pn = P, As) or Pn(3+) (Pn = Sb, Bi) acceptors. The distinction between coordination of a phosphine center to Pn and oxidation of a phosphine ligand is dependent on Pn. The first structurally ve
PMID 26569099

Japanese Journal

Reactions of Molybdenum Hydrides with Organochlorosilanes: Silicon–Silicon Bond Formation under Mild Conditions

Asaeda Takahiro,Lee Joo Yeon,Watanabe Kyosuke,Minato Makoto
Chemistry Letters 43(7), 1005-1007, 2014
… Reactions of molybdenum hydrides containing polydentate phosphinoalkylsilyl ligands with a number of chlorosilanes have been investigated; …
NAID 130004868239

Crystal Structure of 1,3-Dimethylimidazolium Bis(fluorosulfonyl)amide: Unexpectedly High Melting Point Arising from Polydentate Hydrogen Bonding

Fujii Kozo,Mukai Tomohiro,Nishikawa Keiko
Chemistry Letters 43(4), 405-407, 2014
… The single-crystal X-ray structure analysis reveals that this is because the [C1mim]FSA crystal has low coordination ion number and three types of highly symmetric polydentate C–H···O hydrogen bonds. …
NAID 130004868034

Reactions of Molybdenum Tetrahydrido Complex with Halohydrosilanes

Kuramochi Satoru,Kido Yo-hei,Shioda Syunsuke,Minato Makoto,Kakeya Masaki,Osakada Kohtaro
Bulletin of the Chemical Society of Japan 83(2), 165-169, 2010
… The experimental results reported herein provide certain evidence for the involvement of the silylene species in the unusual formation of the present polydentate phosphinoalkyl–silyl ligands. …
NAID 130004152699