Transition Metals and Coordination Compounds

Naming Coordination Compounds

Coordination compounds are complex chemical species consisting of a central transition metal atom or ion bonded to surrounding molecules or ions called ligands. The systematic naming of these compounds follows specific rules to ensure clarity and consistency.

• Coordination compounds are named similarly to ionic compounds, with the cation named before the anion.

• The cation can be either a complex ion or a simple ion.

Key Terms

• Ligand: An ion or molecule that binds to a central metal atom to form a coordination complex.

• Complex ion: A charged species consisting of a central metal ion bonded to one or more ligands.

• Counter ion: An ion that balances the charge of a complex ion in a compound.

Steps for Naming Coordination Compounds

1. Name ligands in alphabetical order.

   • If the ligand is an anion: change the ending to -o (e.g., chloride becomes chloro).

   • If the ligand is neutral: name it as the molecule (e.g., NH3 is ammine), with some exceptions (e.g., H2O is aqua).

   • Use numerical prefixes to indicate the number of each type of ligand:

     • di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), etc.

     • If the ligand name already contains a prefix, use bis- (2), tris- (3), tetrakis- (4), and place the ligand name in parentheses.

2. Name the transition metal after the ligands.

   • If the complex ion is a cation: the metal's name is not modified.

   • If the complex ion is an anion: change the metal's name ending to -ate (sometimes using the Latin name for the metal, e.g., ferrate for iron).

   • Add the oxidation number of the metal in Roman numerals in parentheses after the metal's name.

   • The overall charge of the complex ion is not named in the compound's name.

3. Name the counter ion.

   • If the counter ion is a cation: its name is not changed.

   • If the counter ion is an anion: change the ending to -ide (unless it is a polyatomic ion, in which case the name is not changed).

4. Write the full name of the coordination compound.

   • Name the cation before the anion and add a space in between.

Example: Naming a Coordination Compound

Example: Provide a systematic name for the following coordination compound: [Cr(H2O)5Br]Br2.

• Step 1: Ligands are H2O (aqua, neutral) and Br- (bromo, anion). Alphabetical order: aqua, bromo.

• Step 2: Metal is chromium. The complex ion is a cation, so the name is not modified. Determine the oxidation state of chromium.

• Step 3: Counter ion is Br- (bromide).

• Step 4: Full name: pentaquabromochromium(III) bromide.

Common Ligand Names

Summary Table: Steps for Naming Coordination Compounds

Additional info: The rules for naming coordination compounds are standardized by IUPAC and are essential for clear communication in inorganic chemistry. Understanding these conventions is important for interpreting chemical literature and for laboratory work involving transition metal complexes.