Naming coordination compounds

Writing a formula: the central atom comes first, then the ligands in alphabetical order, all inside square brackets. The charge of a complex ion goes outside the brackets.

Naming a complex, step by step:

• Find the metal's oxidation number. Call it x, add the charges of the ligands, and set the total equal to the charge of the coordination entity (worked out from the counter ions). In K₄[Fe(CN)₆], four K⁺ give the bracket a charge of 4–, so x + 6(–1) = –4, and x = +2.
• Cations first, then anions, as for any salt.
• Inside the entity, name the ligands first, in alphabetical order, then the metal, then its oxidation state in Roman numerals in brackets.

Ligand names to learn: NH₃ is ammine, H₂O aqua, CO carbonyl, Cl⁻ chlorido, CN⁻ cyanido, NO₂⁻ nitrito-N (bonded through N) or nitrito-O (through O), en ethane-1,2-diamine.

Number prefixes: di-, tri-, tetra-, penta-, hexa-. For a ligand whose name already has a number in it, such as en, use bis-, tris-, tetrakis- and put the ligand name in brackets: tris(ethane-1,2-diamine). The prefixes are ignored when putting the ligands in alphabetical order.

If the complex ion is negative, the metal's name ends in -ate: cobaltate, zincate, nickelate; and some take their Latin names, ferrate (iron), cuprate (copper), argentate (silver), aurate (gold). A neutral or positive complex keeps the plain metal name.

Examples: [Co(NH₃)₅Cl]Cl₂ is pentaamminechloridocobalt(III) chloride. K₄[Fe(CN)₆], with a negative complex ion, is potassium hexacyanidoferrate(II). [Ag(CN)₂]⁻ is dicyanidoargentate(I).