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, molecules and ions ...

, a transition metal chloride complex is a coordination complex that consists of a transition metal coordinated to one or more chloride ligand. The class of complexes is extensive.

Bonding

Halides are X-type ligands 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 bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

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

weak field ligand Ligand field theory (LFT) describes the bonding, orbital arrangement, and other characteristics of coordination complexes. It represents an application of molecular orbital theory to transition metal complexes. A transition metal ion has nine valen ...

s. 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 In chemistry, π backbonding, also called π backdonation, is when electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a ''π-acceptor ligand''. It is especially common in the organometallic chemi ...

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.

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 and Cisplatin (''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, copper(II) chloride, iron(II) chloride, and cobalt(II) chloride 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, o ...

Adducts

Metal chlorides form adducts with ethers to give transition metal ether complexes.

References

{{Coordination complexes Chlorometallates Coordination chemistry Coordination complexes Inorganic compounds