Definition: A complex is a central metal ion surrounded by ligands

Examples: [Cu(H2O)6]2+ and [CuCl4]2-

Round brackets, ( ) are used around ligands comprising of more than one element such as:

Water (H2O), ammonia (NH3), hydroxide ions (OH-)

Square brackets, [ ] are used to enclose the complex, with the overall charge written outside

Chloride, Cl- is one element

The name of a complex gives you information about:

The number of each type of ligand The identity of each ligand The identity of the central metal ion and its oxidation

state

Example: [Cr(H2O)4(OH)2]+

4 water (H2O) ligands and 2 hydroxide (OH-) ligands Chromium(III) ion, Cr3+

When there are two or more ligands around the central metal ion, the number is shown by a prefix

Example: [Cu(H2O)6]2+ Name: Hexa

Number of ligands Prefix2 Di3 Tri4 Tetra5 Penta6 Hexa

The identity of each type of ligand is shown by a name This name is not identical to the name of the ligand

Example: [Cu(H2O)6]2+ Name: Hexaaqua

Ligand Name in complexWater Aqua

Ammonia AmmineChloride Chloro

Hydroxide HydroxoCyanide Cyano

The name of the metal changes depending on whether the complex is positively or negatively charged

If the complex is positively charged, the metal is identified by its normal name, with the oxidation state shown in brackets

Example: [Cu(H2O)6]2+ Name: Hexaaquacopper(II)

Example: [Cu(H2O)6]+ Name: Hexaaquacopper(I) Example: [Co(H2O)6]2+ Name: Hexaaquacobalt(II)

If the complex is negatively charged, the oxidation state of the metal is still shown in brackets

But the ending of the metal’s name has the suffix ate added to it

Metal Name in negatively charged complex

Chromium ChromateCobalt CobaltateCopper Cuprate

Iron FerrateManganese Manganate

Metal Name in negatively charged complex

Chromium ChromateCobalt CobaltateCopper Cuprate

Iron FerrateManganese Manganate

Nickel NickelateSilver Argentate

Vanadium Vanadate

It is acceptable to have two letter a’s next to each other, such as hexaaqua or hexaamine

Formula Name[Ag(NH3)2]+ Diamminesilver(I)

[Co(H2O)6]2+ Hexaaquacobalt(II)

[Co(NH3)6]2+ Hexaamminecobalt(II)

[CoCl4]2- Tetrachlorocobaltate(II)

[AgCl2]- Dichloroargenate(I)

[Fe(H2O)6]2+ Hexaaquairon(II)

[Ag(CN)2]- Dicyanoargenate(I)

If two or more ligands are present in a complex, they are named in alphabetical order

It is the name of the ligand which is written in alphabetical order, not the numbering prefix

Examples:

[Cu(H2O)5(OH)]+ Pentaaquahydroxocopper(II)

[Cu(H2O)2(NH3)4]2+ Tetraamminediaquacopper(II)

[Fe(H2O)4(OH)2]+ Tetraaquadihydroxoiron(III)

When you write the formula of a complex:

First write the symbol of the central metal ion Then write the symbols of the ligands in alphabetical

order Include brackets and work out the charge on the outside

Example: Tetraaquadichlorochromium(III) ion

[CrCl2(H2O)4]+ Not [Cr(H2O)4Cl2]+

First write the symbol of the central metal ion Then write the symbols of the ligands in alphabetical

order Include brackets and work out the charge on the outside

Name FormulaDiaquasilver(I) [Ag(H2O)2]+

Hexaaquavanadium(III) [V(H2O)6]3+

Tetracyanonickelate(II) [Ni(CN)4]2-

Tetrachloroferrate(II) [FeCl4]2-

Diaquatetrahydroxochromate(III) [Cr(H2O)2(OH)4]-

Triaaquatrihydroxocuprate(II) [Cu(H2O)3(OH)3]-