Coordination Chemistry

Coordination compounds contain coordinate covalent bonds.

Coordinate covalent bonds are formed when a metal ion reacts with groups of anions or neutral polar molecules.

Coordinate compounds often contain a complex ion along with a counter ion.

CoCl3·6NH

3

or[Co(NH

3)

6]Cl

3

Transition metals have incompletely filled d subshells or form ions with incompletely d subshells.

Transition metals exhibit several oxidation states, the highest oxidation states found in compounds

that contain highly electronegative elements.

V2O

5 Mn2O

7

The ions or molecules that surround the metal in a complex ion are called ligands.

Ligands act as Lewis bases and the transition metal acts as a Lewis acid.

A ligand must have at least one pair of unshared electrons.

The atom bound directly to the metal atom is called the donor atom.

The ethylenediaminetetraacetate plumbate(II) ion

The coordination number in a coordination compound describes the number of donor atoms surrounding the central metal atom in a complex

ion.Coordination number?

A ligand is classified as monodentate, bidentate, or polydentate.

A metal-ethylenediamine complex, such as [Co(en)

3]2+

The oxidation state of a transition metal in a complex ion can be determined by knowing the

overall charge on the complex ion and the charges on the ligands.

What are the oxidation states for the transition metals in K[Au(OH)4],

K4[Fe(CN)

6], [Ru(NH

3)

5(H

2O)]Cl

2, [Cr(NH

3)

6](NO

3)

3, and Fe(CO)

5?

Nomenclature of Coordination Compounds

When naming coordination compounds, say the name of the cation first (regardless of whether its

a metal ion or the complex ion).

In K2[Fe(CN)

6] name K+ first – the name starts with “Potassium”

In [Co(NH3)

4]Cl name [Co(NH

3)

4]+ first – the name starts with

“Tetraammine cobalt (I)”

Within a complex ion the ligands are named first, in alphabetical order, and the metal ion is named last.

The name of the complex ion [Co(NH3)

4]+ is “Tetraammine cobalt (I)”

Anionic ligands names end in the letter “o”. Neutral ligands usually are called by the name of the

molecule (note the exceptions).

When there are two or more ligands use the Greek prefixes di, tri, tetra, penta, and hexa.

The ligands in [Co(NH3)

4Cl

2]+ are named as “tetraamminedichloro”.

When the name of a ligand already contains a Greek prefix, a different set of prefixes is used:

2 bis3 tris

4 tetrakis

The ligands in [Co(en)3]3+ are named as “tris(ethylenediamine)”.

The oxidation state of the metal is given by a Roman numeral in parentheses right after the name of the

metal.

In the complex ion [Cr(NH3)

4Cl

2]+ the chromium ion has a +3 oxidation state

so the name of the complex ion is tetraamminedichlorochromium(III)

If the complex is an anion it's name ends in “ate”.

In K4[Fe(CN)

6] the anion [Fe(CN)

6]4- is called hexacyanoferrate(II) ion.

What are the names of the following coordination compounds?

[Co(NH3)

4Cl

2]Cl

K3[Fe(CN)

6]

[Cr(H2O)

4Cl

2]Cl

[Cr(en)2Cl

2]Br

What are the formulas of the following coordination compounds?

pentaaquabromoruthenium(II) nitrate

bis(ethylenediamine)oxalatovanadium(IV) chloride

sodium hexanitrocobaltate(III)

dibromobis(ethylenediamine)chromium(III) nitrate

tris(ethylenediamine)platinum(IV) sulfate

potassium tetrabromodichloroplatinate(IV)