# Coordination Compound Naming Tool - IUPAC Names, Oxidation State, Isomers

> Free coordination compound tool: get IUPAC and Chinese names, oxidation state, coordination number, geometry, isomers and 18-electron count from a formula.

- URL: https://qilingtools.com/en/chemistry/coordination
- Category: Chemistry Tools (https://qilingtools.com/en/chemistry)
- Tags: [Chemistry](https://qilingtools.com/en/tags/chemistry)
- Last updated: 2026-10-29
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

A coordination compound has an inner coordination sphere — the central metal and its ligands, written in square brackets — and outer-sphere counter-ions. The oxidation state of the metal comes from charge balance: in K₄[Fe(CN)₆] the four K⁺ make the complex ion 4−, each CN⁻ is −1, so iron is +2, the coordination number is 6 and the name is potassium hexacyanidoferrate(II); [Co(NH₃)₆]Cl₃ contains Co(III) and is hexaamminecobalt(III) chloride. This tool has a bracket-aware formula parser and a dictionary of 35 common ligands (NH₃, H₂O, CO, Cl⁻, CN⁻, OH⁻, NO₂⁻/ONO⁻, SCN⁻/NCS⁻, C₂O₄²⁻, en, py, bipy, phen, EDTA, Cp and more, each with charge, denticity, donor atom and names). It accepts single complex ions such as [Co(en)3]^3+ and double complex salts such as [Pt(NH3)4][PtCl4], and turns names like “tetraamminecopper(II) sulfate” or trivial names such as cisplatin, ferrocene and potassium ferricyanide back into formulas. English names follow the IUPAC 2005 recommendations (ligands in alphabetical order, -ido endings, -ate names such as ferrate, cuprate and argentate for complex anions); Chinese names follow the Chinese Chemical Society rules. Stereoisomers are found by enumerating every arrangement under the symmetry operations of the octahedron, square plane or tetrahedron: [Pt(NH₃)₂Cl₂] has cis and trans isomers (cis is the anticancer drug cisplatin), MA₃B₃ has fac and mer forms, [Co(en)₃]³⁺ exists as Δ and Λ enantiomers and [CoCl₂(en)₂]⁺ has three stereoisomers in total, each drawn in 3D. The tool also gives the valence-bond hybridization, d-electron count and 18-electron / EAN count — [Ni(CO)₄] is Ni(0) with 10 + 4 × 2 = 18 valence electrons.

## How to use

1. Type a complex formula such as [Co(NH3)6]Cl3 or K4[Fe(CN)6], an English or Chinese name, or a trivial name — or click an example
2. Read the English and Chinese names, oxidation state, coordination number, inner and outer sphere, geometry and the worked steps
3. Scroll down for 3D isomer drawings and the 18-electron count, and jump to the crystal field tool for d-orbital splitting

## Features

- Bracket-aware formula parser for inner sphere, counter-ions, multiple complex units and charged complex ions
- IUPAC 2005 English names (with charge-number form) and Chinese systematic names
- Name → formula for systematic names and trivial names such as cisplatin, ferrocene, Zeise’s salt and potassium ferrocyanide
- Oxidation state, coordination number (Σ count × denticity) and complex-ion charge with steps
- 35-ligand dictionary with charge, denticity, donor atom and names, distinguishing NO₂⁻/ONO⁻ and SCN⁻/NCS⁻
- Automatic enumeration of geometric and optical isomers for octahedral, square-planar and tetrahedral complexes, with 3D drawings and mirror images
- Valence-bond hybridization (inner/outer orbital), d-electron count, 18-electron rule and effective atomic number
- One-click link to the crystal field calculator for splitting, spin state and magnetic moment

## FAQ

### How do you name a coordination compound in IUPAC style?

Name the cation first and the anion second. Inside the complex, list the ligands in alphabetical order of their names, ignoring multiplying prefixes (di-, tri-, tetra-, bis-, tris-); anionic ligands end in -ido or -ato (chlorido, cyanido, hydroxido, oxalato) and neutral ligands have special names (aqua, ammine, carbonyl, nitrosyl). Then give the metal and its oxidation state in Roman numerals, e.g. diamminedichloridoplatinum(II). If the complex is an anion the metal takes an -ate ending, using Latin stems for some metals: ferrate, cuprate, argentate, aurate, plumbate, stannate — so K₄[Fe(CN)₆] is potassium hexacyanidoferrate(II).

### How do I find the oxidation state and coordination number of the central metal?

First find the charge of the complex ion from the counter-ions: in [CoCl(NH₃)₅]Cl₂ two Cl⁻ outside the brackets make the complex 2+. Subtract the sum of the ligand charges: one Cl⁻ (−1) and five neutral NH₃ give −1, so Co = +2 − (−1) = +3. The coordination number is the number of donor atoms bound to the metal — the sum of count × denticity — so a monodentate ligand counts once and a bidentate ligand such as en or oxalate counts twice: [Co(en)₃]³⁺ has CN 6.

### How many isomers does a coordination complex have?

It depends on the geometry and the ligand set. Square-planar MA₂B₂ such as [Pt(NH₃)₂Cl₂] has cis and trans isomers; octahedral MA₄B₂ has cis and trans, and MA₃B₃ has fac and mer; tetrahedral complexes have no cis/trans isomers. A complex that cannot be superimposed on its mirror image is chiral: [Co(en)₃]³⁺ exists as Δ and Λ enantiomers, and cis-[CoCl₂(en)₂]⁺ is chiral too, so [CoCl₂(en)₂]⁺ has three stereoisomers. This tool enumerates every arrangement and removes duplicates using the symmetry operations, which is more reliable than counting by hand.

### What is the 18-electron rule?

Transition-metal complexes tend to be stable when the metal’s valence electrons plus the electrons donated by the ligands add up to 18, the configuration of the next noble gas. The same idea expressed with atomic numbers is the effective atomic number, EAN = Z − oxidation state + ligand electrons. In [Ni(CO)₄], Ni(0) has 10 valence electrons and each CO donates 2, giving 18 (EAN 36, krypton); [Fe(CN)₆]⁴⁻ is also 18-electron. Square-planar d⁸ complexes such as cisplatin are typically stable with 16 electrons, and the rule works best for carbonyls and other organometallics.

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