1. Dmg Is Which Type Of Ligand Used
2. Dmg Is Which Type Of Ligand 2

Denticity refers to the number of donor groups 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.

• Oxalate ion is a bidentate ligand even though it contains four O atoms which have lone pairs of electrons. Ni(ox) 2 2-In this complex, two oxalate ions are bonded to the Ni atom. The coordination number of 4 results in a square planar structure.
• Types of signaling molecules and the receptors they bind to on target cells. Intracellular receptors, ligand-gated ion channels, G protein-coupled receptors, and receptor tyrosine kinases.

Denticity is different from 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[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.

%INCORRECT% QUESTION 3 OF 5 Which type of ligand is DMG in this complex? Movie monodentate bidentate tridentate tetradentate 1 1%CORRECT% Although there are a total of four bonds from the Ni center to DMG ions, each DMG-ion attaches to the Ni in two places.%INCORRECT% QUESTION 4 OF 5 What is the net charge on the final complex? Denticity refers to the number of donor groups in a single ligand that bind to a central atom in a coordination complex. 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).

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

• Tridentate ligands bind with three atoms, an example being terpyridine. Tridentate ligands usually bind via two kinds of connectivity, called 'mer' and 'fac.' 'fac' stands for facial, the donor atoms are arranged on a triangle around one face of the octahedron. 'mer' stands for meridian, where the donor atoms are stretched out around one half of the octahedron. Cyclic tridentate ligands such as TACN and 9-ane-S3 bind in a facial manner.
• Tetradentate ligands bind with four donor atoms, an example being triethylenetetramine (abbreviated trien). For different central metal geometries there can be different numbers of isomers depending on the ligand's 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 (adjacent to each other). Many naturally occurring macrocyclic ligands are tetradentative, an example being the porphyrin in heme. On an octahedral metal these leave two vacant sites opposite each other.
• 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.

Stability constants[edit]

In general, the stability of a metal complex correlates with the denticity of the ligands, which can be attributed to the chelate effect. Polydentate ligands such as hexa- or octadentate ligands tend to bind metal ions more strongly than ligands of lower denticity, primarily due to entropic factors. Stability constants are a quantitative measure to assess the thermodynamic stability of coordination complexes.

See also[edit]

External links[edit]

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

References[edit]

1. ^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the 'Gold Book') (1997). Online corrected version: (2006–) 'denticity'. doi:10.1351/goldbook.D01594
2. ^von Zelewsky, A. 'Stereochemistry of Coordination Compounds' John Wiley: Chichester, 1995. ISBN047195599X.
3. ^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the 'Gold Book') (1997). Online corrected version: (2006–) 'κ (kappa) in inorganic nomenclature'. doi:10.1351/goldbook.K03366
4. ^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the 'Gold Book') (1997). Online corrected version: (2006–) 'η (eta or hapto) in inorganic nomenclature'. doi:10.1351/goldbook.H01881
5. ^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the 'Gold Book') (1997). Online corrected version: (2006–) 'bridging ligand'. doi:10.1351/goldbook.B00741
6. ^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the 'Gold Book') (1997). Online corrected version: (2006–) 'µ- (mu) in inorganic nomenclature'. doi:10.1351/goldbook.M03659
7. ^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the 'Gold Book') (1997). Online corrected version: (2006–) 'chelation'. doi:10.1351/goldbook.C01012

A spectrochemical series is a list of ligands ordered on ligand strength and a list of metal ions based on oxidation number, group and its identity. In crystal field theory, ligands modify the difference in energy between the d orbitals (Δ) called the ligand-field splitting parameter for ligands or the crystal-field splitting parameter, which is mainly reflected in differences in color of similar metal-ligand complexes.

Spectrochemical series of ligands[edit]

The spectrochemical series was first proposed in 1938 based on the results of absorption spectra of cobalt complexes.^[1]

A partial spectrochemical series listing of ligands from small Δ to large Δ is given below. (For a table, see the ligand page.)

I⁻ < Br⁻ < S²⁻ < SCN⁻ (S–bonded) < Cl⁻ < N₃⁻ < F⁻< NCO⁻ < OH⁻ < C₂O₄²⁻ < O²⁻< H₂O < acac⁻ (acetylacetonate) < NCS⁻ (N–bonded) < CH₃CN < gly (glycine) < py (pyridine) < NH₃ < en (ethylenediamine) < bipy (2,2'-bipyridine) < phen (1,10-phenanthroline) < NO₂⁻ < PPh₃ < CN⁻ < CO

Weak field ligand: H₂O,F-,Cl-,OH-Strong field ligand: CO,CN-,NH₃,PPh₃

Dmg Is Which Type Of Ligand Used

Ligands arranged on the left end of this spectrochemical series are generally regarded as weaker ligands and cannot cause forcible pairing of electrons within the 3d level, and thus form outer orbital octahedral complexes that are high spin. On the other hand, ligands lying at the right end are stronger ligands and form inner orbital octahedral complexes after forcible pairing of electrons within 3d level and hence are called low spin ligands.

However, keep in mind that 'the spectrochemical series is essentially backwards from what it should be for a reasonable prediction based on the assumptions of crystal field theory.'^[2] This deviation from crystal field theory highlights the weakness of crystal field theory's assumption of purely ionic bonds between metal and ligand.

The order of the spectrochemical series can be derived from the understanding that ligands are frequently classified by their donor or acceptor abilities. Some, like NH₃, are σ bond donors only, with no orbitals of appropriate symmetry for π bonding interactions. Bonding by these ligands to metals is relatively simple, using only the σ bonds to create relatively weak interactions. Another example of a σ bonding ligand would be ethylenediamine, however ethylenediamine has a stronger effect than ammonia, generating a larger ligand field split, Δ.

Ligands that have occupied p orbitals are potentially π donors. These types of ligands tend to donate these electrons to the metal along with the σ bonding electrons, exhibiting stronger metal-ligand interactions and an effective decrease of Δ. Most halide ligands as well as OH⁻ are primary examples of π donor ligands.

When ligands have vacant π* and d orbitals of suitable energy, there is the possibility of pi backbonding, and the ligands may be π acceptors. This addition to the bonding scheme increases Δ. Ligands that do this very effectively include CN⁻, CO, and many others.^[3]

Spectrochemical series of metals[edit]

The metal ions can also be arranged in order of increasing Δ, and this order is largely independent of the identity of the ligand.^[4]

Mn²⁺ < Ni²⁺ < Co²⁺ < Fe²⁺ < V²⁺ < Fe³⁺ < Cr³⁺ < V³⁺ < Co³⁺

In general, it is not possible to say whether a given ligand will exert a strong field or a weak field on a given metal ion. However, when we consider the metal ion, the following two useful trends are observed:

• Δ increases with increasing oxidation number, and
• Δ increases down a group.^[4]

Dmg Is Which Type Of Ligand 2

See also[edit]

References[edit]

• Zumdahl, Steven S. Chemical Principles Fifth Edition. Boston: Houghton Mifflin Company, 2005. Pages 550-551 and 957-964.
• D. F. Shriver and P. W. Atkins Inorganic Chemistry 3rd edition, Oxford University Press, 2001. Pages: 227-236.
• James E. Huheey, Ellen A. Keiter, and Richard L. Keiter Inorganic Chemistry: Principles of Structure and Reactivity 4th edition, HarperCollins College Publishers, 1993. Pages 405-408.

1. ^R. Tsuchida (1938). 'Absorption Spectra of Co-ordination Compounds. I.'Bull. Chem. Soc. Jpn. 13 (5). doi:10.1246/bcsj.13.388.
2. ^7th page of http://science.marshall.edu/castella/chm448/chap11.pdf
3. ^Miessler, Gary; Tarr, Donald (2011). Inorganic Chemistry (4th ed.). Prentice Hall. pp. 395–396. ISBN978-0-13-612866-3.
4. ^ ^abhttp://www.everyscience.com/Chemistry/Inorganic/Crystal_and_Ligand_Field_Theories/b.1013.php