--- title: "Coordination Compounds: Naming, Geometry and Isomerism" description: "A complex is written and named by a strict convention that records the metal, its oxidation state, and every ligand in order. The same convention exposes the several ways two complexes can share a for" canonical: https://lightmysky.com/learn/science/coordination-compounds-naming-geometry-and-isomerism-mt_rkHM3jL3Ri source: https://lightmysky.com/learn/science/coordination-compounds-naming-geometry-and-isomerism-mt_rkHM3jL3Ri.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Coordination Compounds: Naming, Geometry and Isomerism A complex is written and named by a strict convention that records the metal, its oxidation state, and every ligand in order. The same convention exposes the several ways two complexes can share a formula and differ. Subject: Science · Area: Chemistry · Ages 19 to 20 Page: https://lightmysky.com/learn/science/coordination-compounds-naming-geometry-and-isomerism-mt_rkHM3jL3Ri ## Ready when they can - Names a complex from its formula and writes the formula back from the name - Works out the coordination number and the oxidation state of the metal for charged and neutral ligands - Draws cis and trans and fac and mer isomers for the appropriate geometries - Distinguishes linkage, ionisation and coordination isomerism with an example of each ## Lesson: Naming complexes and spotting isomers A complex ion is named ligands first, in alphabetical order with di-, tetra- or hexa- for the counts, then the metal with its oxidation state in roman numerals. Water is aqua, ammonia is ammine, and anionic ligands end in -o, as in chlorido and cyanido. A salt names the cation before the anion, as in tetraamminecopper(II) sulfate. The rule runs backwards too: diamminesilver(I) chloride is [Ag(NH3)2]Cl, with two ammonias inside the brackets and one chloride outside. Two numbers complete the description. The oxidation state comes from balancing charges. In K3[Fe(CN)6], three K+ give +3 and six CN- give -6, so iron must be +3 for the compound to be neutral. The coordination number counts donor atoms bonded to the metal, not ligands. In [Co(en)2Cl2]+, each ethane-1,2-diamine (en) binds through two nitrogens, so 2 x 2 + 2 = 6. *(drawing: The metal's oxidation state is whatever makes the charges add up.)* **Example.** One formula can give several real compounds. In a square planar complex, two matching ligands can sit side by side (cis) or across from each other (trans). In an octahedral complex with four of one ligand and two of another, such as [Co(NH3)4Cl2]+, the chlorides can be cis, 90 degrees apart, or trans, 180 degrees apart. With three of each ligand, the matching three can share one triangular face (fac) or lie in one plane through the metal with two opposite (mer). Other isomers swap pieces rather than positions. Linkage isomers swap the donor atom of one ligand, such as NO2- binding through N (nitro) or through O (nitrito). Ionisation isomers swap an ion between inside and outside the brackets, as in [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br. Coordination isomers swap ligands between a complex cation and a complex anion, as in [Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6]. **Recap.** Name ligands before metal with the oxidation state, count donor atoms for the coordination number, and sort isomers by what moved. *Original chemistry lesson and assessment text written for os-taxonomy.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Acid-Base Models Beyond Bronsted: Lewis, Solvents and Hard and Soft](https://lightmysky.com/learn/science/acid-base-models-beyond-bronsted-lewis-solvents-and-hard-and-soft-mt_jarui-9yfx) - [Complex Ions, Ligands and Their Shapes](https://lightmysky.com/learn/science/complex-ions-ligands-and-their-shapes-mt_xxWYYqgZp_) ## Opens up - [Porous Frameworks: Pores, Guests and Stability](https://lightmysky.com/learn/science/porous-frameworks-pores-guests-and-stability-mt_csqPeYIhN6) - [Metals in Biology: Active Sites, Electron Transfer and Chelation](https://lightmysky.com/learn/science/metals-in-biology-active-sites-electron-transfer-and-chelation-mt_gKhjhRXfMU) - [Crystal field theory and the splitting of d orbitals](https://lightmysky.com/learn/science/crystal-field-theory-and-the-splitting-of-d-orbitals-mt_YfIBGXj8su)