Coordination Compound Naming — Chemistry Mnemonic
Target: mnemonic for naming coordination compounds IUPAC rules
Why is this hard to memorize?
Naming coordination compounds follows IUPAC rules that are tested extensively in JEE and NEET. The rules are systematic but have many parts: name ligands alphabetically before the metal, use specific suffixes (-o for anionic ligands, aqua for water, ammine for NH₃), indicate oxidation state in Roman numerals, and use different endings for cation vs anion complexes. The order is: cation first then anion (if ionic), ligands in alphabetical order, then metal name with oxidation state. For anionic complexes, the metal name gets the -ate suffix (often using Latin roots: ferrate, cuprate, argentate).
Classic mnemonics you should know
"Ligands(alphabetical) + Metal(Roman numeral) — "LAM" — Ligands Alpha Metal"
Step 1: Name cation first, anion second (if ionic). Step 2: Within the complex: ligands in alphabetical order, then metal with oxidation state in parentheses. "LAM" = Ligands Alphabetical, then Metal.
"Anionic → -o (chlorido, hydroxido). Neutral → no change (aqua, ammine). Cationic → -ium (nitrosonium)"
Anionic ligands end in -o: Cl⁻ → chlorido, OH⁻ → hydroxido, CN⁻ → cyanido. Neutral ligands keep their name: H₂O = aqua, NH₃ = ammine (double m!), CO = carbonyl, NO = nitrosyl. Only the four special neutrals have unique names.
"If complex is the ANION → metal gets -ate: Iron → Ferrate, Copper → Cuprate, Silver → Argentate"
When the complex ion is negatively charged, use Latin-based name + ate: Fe → ferrate, Cu → cuprate, Ag → argentate, Au → aurate, Sn → stannate, Pb → plumbate. Positive complex ions use the normal English metal name.
The complete list
- Cation named first, anion second
- Ligands in alphabetical order
- Anionic ligands: -o suffix
- Neutral ligands: aqua, ammine, carbonyl, nitrosyl
- Metal oxidation state in Roman numerals
- Anionic complex: metal gets -ate
- Multiplying prefixes: di, tri, tetra, penta, hexa
- Complex prefixes: bis, tris, tetrakis (for multi-word ligands)
Frequently asked questions
What is the correct order for naming ligands?
Alphabetical order by ligand name (ignoring multiplying prefixes like di, tri). For example: ammine, chlorido, hydroxido → listed as ammine, chlorido, hydroxido (a before c before h). Prefixes (di-, tri-) do not affect alphabetization — so "diammine" still alphabetizes under "a."
Why does NH₃ become "ammine" with double m?
To distinguish it from "amine" (organic –NH₂ group). In coordination chemistry, "ammine" (double m) specifically means NH₃ acting as a neutral ligand. "Amine" (single m) refers to organic compounds like methylamine. This is a common trick question in NEET.
How do I calculate the oxidation state of the central metal?
Set up: (charge of complex ion) = (oxidation state of metal) + (sum of charges of all ligands). For [Fe(CN)₆]⁴⁻: −4 = x + 6(−1), so x = +2. For [Co(NH₃)₆]³⁺: +3 = x + 6(0), so x = +3. Neutral ligands contribute 0 charge, anionic ligands contribute their charge.
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