Ligand

ligandsligand exchangebidentate ligandambidentate ligandligand exchange reactionbidentateBiochemistry#Receptor/ligand binding affinitybulky ligandL-type ligandligand binding
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex.wikipedia
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Functional group

groupfunctional groupsmoiety
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex.
Functional groups binding to a central atom in a coordination complex are called ligands.

Coordination complex

coordination chemistrycomplexcomplexes
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The composition of coordination complexes have been known since the early 1800s, such as Prussian blue and copper vitriol.
In chemistry, a coordination complex consists of a central atom or ion, which is usually metallic and is called the coordination centre, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents.

Hapticity

ηη 5 η'' 5
Ligands are classified in many ways, including: charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity).
Hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms.

Metal ammine complex

ammineammine complexammine (ammonia) complex
The theory allows one to understand the difference between coordinated and ionic chloride in the cobalt ammine chlorides and to explain many of the previously inexplicable isomers.
In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia (NH 3 ) ligand.

Lewis acids and bases

Lewis acidLewis baseLewis acids
Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands".
Metal ions such as Na +, Mg 2+, and Ce 3+, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base[citation needed].

HSAB theory

hardsofthard acid
Ligands and metal ions can be ordered in many ways; one ranking system focuses on ligand 'hardness' (see also hard/soft acid/base theory).
This is especially so in transition metal chemistry, where numerous experiments have been done to determine the relative ordering of ligands and transition metal ions in terms of their hardness and softness.

Spectrochemical series

crystal-field splitting parameterligand field parametersligand field splitting
This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.
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.

Coordination number

coordinationcoordinatedhexacoordinate
The ion/molecule/atom surrounding the central ion/molecule/atom is called a ligand.

Carbon monoxide

COcarbon monoxide (CO)carbon monoxide poisoning
L ligands are derived from charge-neutral precursors and are represented by amines, phosphines, CO, N 2, and alkenes. Thus, the halides and pseudohalides are important anionic ligands whereas ammonia, carbon monoxide, and water are particularly common charge-neutral ligands.
In coordination complexes the carbon monoxide ligand is called carbonyl.

Denticity

bidentatemonodentateunidentate
Ligands are classified in many ways, including: charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity). A ligand that binds through two sites is classified as bidentate, and three sites as tridentate.
Denticity refers to the number of donor groups in a single ligand that bind to a central atom in a coordination complex.

Organometallic chemistry

organometallicorganometallic compoundorganometallic compounds
Especially in the area of organometallic chemistry, ligands are classified as L and X (or combinations of the two).
Many complexes feature coordination bonds between a metal and organic ligands.

Ethylenediamine

ethylene diamineenEthylenediamines
A classic bidentate ligand is ethylenediamine, which is derived by the linking of two ammonia groups with an ethylene (−CH 2 CH 2 −) linker.
Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C 2 H 4 (NH 2 ) 2.

Tridentate ligand

tridentatetri-
A ligand that binds through two sites is classified as bidentate, and three sites as tridentate.
A tridentate ligand (or terdentate ligand) is a ligand that has three atoms that can function as donor atoms in a coordination complex.

Crystal field theory

crystal fieldcrystal field stabilization energycrystal field splitting
According to crystal field theory, the interaction between a transition metal and ligands arises from the attraction between the positively charged metal cation and the negative charge on the non-bonding electrons of the ligand.

Chelation

chelatechelatingchelating agent
Ligands that bind via more than one atom are often termed chelating.
It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central atom.

Pi backbonding

π backbondingback bondingback-bonding
The metal–ligand bond can be further stabilised by a formal donation of electron density back to the ligand in a process known as back-bonding. In this case a filled, central-atom-based orbital donates density into the LUMO of the (coordinated) ligand.
It is especially common in the organometallic chemistry of transition metals with multi-atomic ligands such as carbon monoxide, ethylene or the nitrosonium cation.

Alfred Werner

WernerWerner, Alfred
The key breakthrough occurred when Alfred Werner reconciled formulas and isomers.
In 1893, Werner was the first to propose correct structures for coordination compounds containing complex ions, in which a central transition metal atom is surrounded by neutral or anionic ligands.

Bite angle

The "bite angle" refers to the angle between the two bonds of a bidentate chelate.
This geometric parameter is used to classify chelating ligands, including those in organometallic complexes.

Coordination polymer

coordination polymerspolymeric
Virtually all inorganic solids with simple formulas are coordination polymers, consisting of metal ion centres linked by bridging ligands.
A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands.

Porphyrin

porphyrinscoproporphyrinuroporphyrin
Heme is a good example: the iron atom is at the centre of a porphyrin macrocycle, being bound to four nitrogen atoms of the tetrapyrrole macrocycle.
Porphyrins are the conjugate acids of ligands that bind metals to form complexes.

Prussian blue

Radiogardaseferric ferrocyanideTurnbull's blue
The composition of coordination complexes have been known since the early 1800s, such as Prussian blue and copper vitriol.
The Fe(II) centers, which are low spin, are surrounded by six carbon ligands in an octahedral configuration.

Heme

haemheme grouphaeme
Heme is a good example: the iron atom is at the centre of a porphyrin macrocycle, being bound to four nitrogen atoms of the tetrapyrrole macrocycle.
During the detection of diatomic gases, the binding of the gas ligand to the heme iron induces conformational changes in the surrounding protein.

Vaska's complex

IrCl(CO)(PPh 3 ) 2 IrCl(CO)(P(C 6 H 5 ) 3 ) 2 IrCl(CO)(PPh3)2
Thus, the complex IrCl(CO)(PPh 3 ) 2 is classified as an MXL 3 complex, since CO and the two PPh 3 ligands are classified as Ls.
This square planar diamagnetic organometallic complex consists of a central iridium atom bound to two mutually trans triphenylphosphine ligands, carbon monoxide, and a chloride ion.

Pseudohalogen

pseudohalidepseudohalides(pseudo)halide
Thus, the halides and pseudohalides are important anionic ligands whereas ammonia, carbon monoxide, and water are particularly common charge-neutral ligands.
Ps–Ps or Ps–X (where Ps is a pseudohalogen group), such as cyanogen; pseudohalide anions, such as cyanide ion; inorganic acids, such as hydrogen cyanide; as ligands in coordination complexes, such as ferricyanide; and as functional groups in organic molecules, such as the nitrile group.

Ligand cone angle

cone angleTolman cone anglesmall
The size of a ligand is indicated by its cone angle.
The ligand cone angle (a common example being the Tolman cone angle or θ) is a measure of the steric bulk of a ligand in a transition metal complex.