Complex Ions

Naming Complex Ions

What is a complex ion?

When naming complex ions, there are many rules you need to follow. A complex ion has two parts; a metal ion or atom and an anion. The metal ion is often attached to several neutral molecules causing it to be a coordination complex. The anion is known as a ligand. Ultimately the complex will be neutral.

Steps to naming a complex ion/coordination complex:

ALWAYS name the cation first!
When you reach the complex ion in a complex, name the ligand first, (alphabetical order)
When naming the anion ligands, the -o ending will always stay.
When naming the cation ligands, the endings will change.
The -ide changes to -o
The -ate changes to -ato
The -ite changes to -ito
Neutral ligands do not have spelling changes
EXCEPT: water, ammonia, and carbon monoxide
Use number prefixes attached to the front of every complex ion denoting the number of molecules
After the ligand has been named, label the central metal. Add the suffix -ate if the metal is an anion. If it is not, simply write the name of the metal (i.e. Co= cobalt or cobaltate)
Write the oxidation number of the metal at the end in parenthesis.

Ligand names (Not all, but some important ones)

Anions

F- Fluoro

Cl- Chloro

Br- Bromo

I- Iodo

OH- Hydroxo

CN- Cyano

Neutral Molecules

H2O Aqua
NH3 Ammine

CH3NH2 Methylamine

CO Carbonyl

NO Nitrosyl

Common Metal Ions

Iron Ferrate

Copper Cuprate

Lead Plumbate

Silver Argentate

Gold Aurate

Tin Stannate

Examples:

1. [Co(NH3)5Cl]Cl2

Name: pentaamminechlorocobalt(III)

Explanation: The ligands are Cl- and NH3. There are five NH3 molecules which result in "pentaammine." The chloride ion is called chloro and the oxidation state of cobalt is +3.

2. Na2[NiCl4]

Name: sodium tetrachloronickelate(II)

Explanation: In this case, the complex ion acts as the anion, therefore we add the -ate. Otherwise, we follow the rules mentioned above verbatim.

3. [Cr(NH3)3(H2O)3]Cl3

Name: triamminetriaquachromium(III) chloride

Explanation: The complex ion is a ligand. The charge on the complex ion is +3. The oxidation number is +3.

Complex Ion Formations

When dealing with complex ion formations, you will always be given a ligand and a transition metal ion to bond together. The metal acts as an ion and the ligand is added on to the metal. When determining the number of ligands to attach, we must look at the coordination numbers. This is the number of bonds formed by the metal ion to lingands in complex ions and varies based on the electron configuration, charge, and size of the transition metal ion. Ligands always have a lone pair of electrons to bond with the metal ion.

Common coordination numbers for metal ions:

(+1 Charges)
Au+ 2,4
Ag+ 2
Cu+ 2,4

(+2 Charges)

Zn+2 4,6
Cu+2 4,6
Ni+2 4,6
Co+2 4,6
Fe+2 6
Mn+2 4,6

(+3 Charges)

Au+3 4
Co+3 6
Cr+3 6
Sc+3 6

*Tip: Try doubling the charge to find the coordination number!

Example Reactions; Complex Ion Formations:

1. Ag+ +2(CN)- <----> Ag(CN)2-

Explanation: Silver metal is the metal ion. Cyanide is the ligand. The coordination number is 2.

2. Cu+2 +4NH3<----> Cu(NH3)4+2

Explanation: Copper is the metal ion. Ammonium is the ligand. The coordination number of the copper ion in this case is 4.

3. Zn(OH)2 + OH- <----> Zn(OH)4 2-

Explanation: Zinc acts as the ion while hydroxide is the ligand. Zinc carries a coordination number of 4 since we are using the +2 form of it.

4. Fe+3 + SCN- <----> FeSCN+2

Explanation: Iron is the transition metal ion. Sulfur cyanide is our ligand. The number of coordination bonds iron has is 6.

What a complex ion looks like

Complex ions come in many distinct shapes and sizes. Each complex ion has an appearance different from the next. Here are just a few of the endless possible complex ion diagrams.