Naming Complex Ions and Questions To Try

Rules for naming the complex ion when given the formula in square brackets eg: [Fe(CN)₆]^4-

Rules :

Name the ligands first, in alphabetical order, then the metal atom or ion.

Note: The metal atom or ion is written before the ligands in the chemical formula.

For negatively charged ligands the name ends in "-o"; so for example chloride becomes chloro, bromide becomes bromo, fluoride becomes fluoro, hydroxide becomes hydroxo, cyanide CN^- becomes cyanido and C₂O₄^2- oxalato

For neutral ligands, the common name of the molecule is used e.g. H₂NCH₂CH₂NH₂ethylenediammine). Important exceptions: water is called ‘aqua’, ammonia is called ‘ammine’.

3. If there are more than one of each type of ligand then Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-.

Numerical Prefixes

di, tri, tetra, penta, hexa, hepta and octa

4. After naming the ligands, name the central metal. If the complex ion is a positively charged ion overall, the metal is named the same as the element. For example, Co is called cobalt and Pt is called platinum, copper is called copper. However, if the complex ion is a negative ion overall then the name of the metal should end with the –ate. For example, Co in a negative ion complex is called cobaltate and Pt is called platinate. For some metals, the Latin names are used in e.g. Fe is called ferrate and Cu becomes cuprate

5 The oxidation state of the metal is then added in Roman Numerals.

Test yourself – get the name from the formula :

Question 1 [Cr(NH₃)₃(H₂O)₃]³⁺

Question 2 [Pt(NH₃)₅Cl]³⁺

Question 3 [Fe(CN)₆]^4-

Question 4 [NiCl₄]^2-

Answers below .....

Question - Get the Formula of the complex ion from the Name

When writing the formula of a complex ion when given the name, a different set of rules applies :
The symbol of the metal is written first, then negatively charged ligands, followed by the neutral ligands:

Question 1 hexaammineiron(III)

Question 2 tetrachlorocuprate(II)

Question 3 hexafluorocobaltate(III)
Question 4 tetraaquadihydroxoiron(III)
Question 5 tetraamminediaquacopper(II) ion.

Answers below ....

^{Answers to "Get the name from the Formula"

Answer 1 triamminetriaquachromium(III)
Answer 2 pentaamminechloroplatinum(IV)
Answer 3 hexacyanidoferrate(II)
Answer 4 tetrachloronickelate(II)

Answers to "Get the Formula of the complex ion from the Name"
Answer 1 [Fe(NH₃)₆]³⁺
Answer 2 [CuCl₄]^2-
Answer 3 [CoF₆]^3-
^{Answer 4}[Fe(OH)₂(H₂O)₄]⁺
_{Answer 5}[Cu(NH₃)₄(H₂O)₂]²⁺}