What it does
A coordination compound has a metal atom or ion at the centre, held by ligands: ions or molecules that each give it a lone pair of electrons. The metal and its ligands are written inside square brackets, such as [Co(NH₃)₆]³⁺, and any counter ions outside the brackets balance the charge.
- Build it. Pick a metal, its oxidation state and up to six donor atoms’ worth of ligands with the + and − buttons. Bidentate ligands (ethane-1,2-diamine, oxalato) count twice. If the complex is charged, pick a counter ion; the page offers only the ones with the right sign.
- Formula and name. The formula follows the bracket rules; the name follows the IUPAC rules schools use: ligands alphabetically, -ido for anions, aqua, ammine and carbonyl for neutral ones, the metal’s oxidation state in Roman numerals, and -ate when the complex is negative (ferrate, cuprate, argentate).
- Facts. Coordination number and the usual shape for it, the charge on the complex ion with the working, how many ions one formula unit gives in water, and Werner’s test: how many moles of AgCl silver nitrate precipitates, because only the chloride outside the brackets is free.
- Examples. Tap Werner’s three cobalt ammine chlorides, the two potassium cyanidoferrates, nickel tetracarbonyl and more.
This fits Class 12 Chemistry: coordination compounds (Werner’s theory, definitions such as ligand, coordination number and oxidation number, IUPAC nomenclature). To see why these complexes are coloured and magnetic, go on to the crystal field; to practise oxidation states in general, use the oxidation number finder tool; and to see the shapes, try VSEPR shape viewer.
How to use it
- Tap an example, or choose a metal and an oxidation state.
- Add ligands with + and remove them with −. The coordination number so far is shown above the list; + is greyed out at 6.
- Choose a counter ion if the complex is charged.
- Read the formula, the name and the facts. Follow the charge working under them.
- Try the Check yourself questions.
Worked example
Werner’s CoCl₃·5NH₃: cobalt(III) with five ammonia and one chloride inside the brackets. Charge = +3 + 1 × (−1) = +2, so two chloride ions sit outside: [CoCl(NH₃)₅]Cl₂, named pentaamminechloridocobalt(III) chloride. The coordination number is 6 (octahedral); it gives 3 ions in water, and 1 mol precipitates 2 mol of AgCl. CoCl₃·6NH₃ gives 3 mol and CoCl₃·4NH₃ only 1, which is how Werner worked out which chlorides were bound to the metal.
K₃[Fe(CN)₆]: +3 + 6 × (−1) = −3, so the complex is an anion and the name ends in -ate: potassium hexacyanidoferrate(III). Change iron to +2 and you get K₄[Fe(CN)₆], potassium hexacyanidoferrate(II).
[Co(en)₃]Cl₃: three bidentate ethane-1,2-diamine ligands give coordination number 6; the name is tris(ethane-1,2-diamine)cobalt(III) chloride.
Tips
- “Ammine” (two m’s) is ammonia as a ligand; “amine” is an organic compound.
- The prefixes di-, tri-, tetra- don’t count when you sort ligands: tetraammine comes before dichlorido because a comes before c.
- Older names (chloro, cyano) are still seen; this page uses the current -ido endings.
FAQ
Does it know which complexes really exist? No. It applies the naming rules to whatever you build and warns when the coordination number is unusual, but it does not check that a compound has been made.
Is anything saved? No. Everything runs in your browser and nothing is stored or sent.
Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.
Where the numbers come from
- The naming follows the IUPAC 2005 recommendations for inorganic nomenclature as taught in schools (ligands in alphabetical order, -ido anion names, -ate for anionic complexes, Roman-numeral oxidation states, bis/tris for ligands such as ethane-1,2-diamine). Werner's silver chloride test is classic chemistry.
- The example complexes are well-known textbook compounds; their names were checked in the tests against names written out by hand from the rules. Nothing is copied from any textbook.
- Drawings and wording are fibub's own. Nothing you enter is stored or sent anywhere.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.