In chemistry, a transition metal chloride complex is a

coordination complex 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. Many ...

that consists of a

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that c ...

coordinated to one or more

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

ligand 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 bonding with the metal generally involves formal donation of one or more of the ligand's ele ...

. The class of complexes is extensive.

Bonding

Halides are X-type

s in

coordination 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 chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing ...

. They are both σ- and π-donors. Chloride is commonly found as both a terminal ligand and a

bridging ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually ...

. The halide ligands are weak field ligands. Due to a smaller crystal field splitting energy, the homoleptic halide complexes of the first transition series are all high spin. Only rCl₆sup>3− is exchange inert. Homoleptic metal halide complexes are known with several stoichiometries, but the main ones are the hexahalometallates and the tetrahalometallates. The hexahalides adopt octahedral coordination geometry, whereas the tetrahalides are usually tetrahedral. Square planar tetrahalides are known for Pd(II), Pt(II), and Au(III). Examples with 2- and 3-coordination are common for Au(I), Cu(I), and Ag(I). Due to the presence of filled p_π orbitals, halide ligands on transition metals are able to reinforce π-backbonding onto a π-acid. They are also known to labilize ''cis''-ligands.

Homoleptic complexes

Homoleptic complexes (complexes with only chloride ligands) are often common reagents. Almost all examples are

anions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

1st row

2nd row

Some homoleptic complexes of the second row transition metals feature metal-metal bonds.

3rd row

Heteroleptic complexes

Heteroleptic complexes containing chloride are numerous. Most hydrated metal halides are members of this class.

Hexamminecobalt(III) chloride Hexaamminecobalt(III) chloride is the chemical compound with the formula

o(NH3)6 O, or o, is the fifteenth letter and the fourth vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''o'' (pronounced ), plu ...

l3. It is the chloride salt of the coordination complex

+, which is considered an archetypal "Werner complex", named after the pioneer of coordination ...

and

Cisplatin Cisplatin is a chemotherapy medication used to treat a number of cancers. These include testicular cancer, ovarian cancer, cervical cancer, breast cancer, bladder cancer, head and neck cancer, esophageal cancer, lung cancer, mesothelio ...

(''cis''-Pt(NH₃)₂Cl₂) are prominent examples of metal-ammine-chlorides.

Hydrates

As indicated in the table below, many hydrates of metal chlorides are molecular complexes. These compounds are often important commercial sources of transition metal chlorides. Several hydrated metal chlorides are not molecular and thus are not included in this tabulation. For example the dihydrates of manganese(II) chloride,

nickel(II) chloride Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for chem ...

, copper(II) chloride, iron(II) chloride, and

cobalt(II) chloride Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula . The compound forms several hydrates ·''n'', for ''n'' = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed.M. T. Saug ...

are

coordination polymer A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2, ...

Adducts

Metal chlorides form adducts with ethers to give

transition metal ether complex In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, mole ...

es.

References

{{Coordination complexes Chlorometallates Coordination chemistry Coordination complexes Inorganic compounds