Nomenclature of Coordination Compounds — Revision Notes

⚡ 30-Second Revision

Cation first, then anion.
Ligands first (alphabetical), then metal.
Anionic ligands: — end in '-o' (e.g., chloro, cyano, oxalato).
Neutral ligands: — special names (aqua $ext{H}_2\text{O}$, ammine $ext{NH}_3$, carbonyl $ext{CO}$, nitrosyl $ext{NO}$), others retain name (ethylenediamine).
Prefixes: — di-, tri-, tetra- for simple ligands; bis-, tris-, tetrakis- for complex ligands (in parentheses).
Oxidation State: — Roman numeral in parentheses after metal (e.g., (II), (III)).
Metal Name: — Unchanged if complex is cationic/neutral (e.g., cobalt, platinum). Ends in '-ate' if complex is anionic (e.g., ferrate, cuprate, argentate).
Bridging Ligands: — $mu$- prefix (e.g., $mu$-hydroxo).
Alphabetical Order: — Ignore prefixes (di-, tri-, etc.) when alphabetizing ligands.

2-Minute Revision

Nomenclature of coordination compounds follows strict IUPAC rules. Always name the cation before the anion. Within the coordination sphere, ligands are named first, in alphabetical order, followed by the central metal.

Remember to ignore numerical prefixes (di-, tri-, bis-, tris-) when determining alphabetical order. Anionic ligands typically end in '-o' (e.g., chloro, cyano), while neutral ligands often have special names like 'aqua' for $ext{H}_2\text{O}$ and 'ammine' for $ext{NH}_3$.

Use simple prefixes (di-, tri-) for simple ligands and multiplicative prefixes (bis-, tris-) for complex ligands (those already containing a prefix or multi-atom). The oxidation state of the central metal is indicated by a Roman numeral in parentheses.

Crucially, if the coordination complex is anionic, the metal's name will end in '-ate' (e.g., ferrate, cuprate); otherwise, it retains its common name. For ambidentate ligands, specify the bonding atom (e.

g., nitrito-N). Practice calculating oxidation states accurately and applying the '-ate' rule correctly, as these are common error points.

5-Minute Revision

To master coordination compound nomenclature for NEET, a systematic approach is essential. Start by identifying the cation and anion of the entire compound; the cation is always named first. Next, focus on the coordination sphere.

Within this, ligands are named before the central metal. Ligands are listed in alphabetical order, and it's critical to remember that numerical prefixes (di-, tri-, tetra-, bis-, tris-) are *not* considered for alphabetization.

For example, 'diammine' comes before 'dichloro' because 'a' of ammine precedes 'c' of chloro.

Ligand naming conventions are specific: anionic ligands typically end in '-o' (e.g., $ext{Cl}^-$ as chloro, $ext{CN}^-$ as cyano, $ext{C}_2\text{O}_4^{2-}$ as oxalato). Neutral ligands usually retain their common names (e.

g., pyridine, ethylenediamine), but a few have special names like 'aqua' ($ext{H}_2\text{O}$), 'ammine' ($ext{NH}_3$), 'carbonyl' ($ext{CO}$), and 'nitrosyl' ($ext{NO}$). The number of simple ligands is indicated by prefixes like di-, tri-, tetra-, while complex ligands (like ethylenediamine) use bis-, tris-, tetrakis-, with the ligand name enclosed in parentheses.

The oxidation state of the central metal is calculated by summing the charges of all ligands and equating it to the overall charge of the complex ion. This oxidation state is then indicated by a Roman numeral in parentheses immediately after the metal's name.

Finally, the metal's name itself depends on the complex's charge: if the complex ion is anionic, the metal name ends in '-ate' (e.g., iron becomes ferrate, copper becomes cuprate); if the complex is cationic or neutral, the metal name remains unchanged.

For example, $[\text{Co(NH}_3)_6]\text{Cl}_3$ is Hexaamminecobalt(III) chloride, while $ext{K}_4[\text{Fe(CN)}_6]$ is Potassium hexacyanoferrate(II). Special cases like ambidentate ligands (e.g., nitrito-N vs.

nitrito-O) and bridging ligands ($mu$-prefix) should also be reviewed. Consistent practice with diverse examples is the best way to solidify these rules.

Prelims Revision Notes

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General Rule: — Cation is named first, followed by the anion. This applies even if the complex is the anion or cation.
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Naming the Coordination Sphere: — Ligands are named first, then the central metal atom/ion.
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Ligand Alphabetical Order: — Ligands are listed in alphabetical order. Numerical prefixes (di-, tri-, bis-, tris-) are *ignored* when determining alphabetical order. (e.g., 'ammine' before 'chloro').
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Ligand Naming:

* Anionic Ligands: End in '-o'. Examples: $ext{Cl}^-$ (chloro), $ext{CN}^-$ (cyano), $ext{OH}^-$ (hydroxo), $ext{SO}_4^{2-}$ (sulfato), $ext{C}_2\text{O}_4^{2-}$ (oxalato), $ext{NO}_2^-$ (nitrito-N or nitro), $ext{ONO}^-$ (nitrito-O or nitrito).

* Neutral Ligands: Common names or special names. Examples: $ext{H}_2\text{O}$ (aqua), $ext{NH}_3$ (ammine), $ext{CO}$ (carbonyl), $ext{NO}$ (nitrosyl), 'en' (ethylenediamine), 'py' (pyridine).

* Cationic Ligands: Rare, end in '-ium' (e.g., hydrazinium).

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Number of Ligands:

* Simple Ligands: Use di-, tri-, tetra-, penta-, hexa- (e.g., dichloro, triammine). * Complex Ligands: Use bis-, tris-, tetrakis- (ligand name in parentheses) when the ligand name already contains a numerical prefix or is polydentate (e.g., bis(ethylenediamine)).

1
Oxidation State of Metal: — Calculated from the charges of ligands and the overall complex charge. Indicated by Roman numeral in parentheses immediately after the metal name (e.g., (II), (III)).
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Metal Name Suffix:

* Cationic or Neutral Complex: Metal name is used as is (e.g., cobalt, platinum, copper). * Anionic Complex: Metal name ends in '-ate'. Use Latin roots for some metals (e.g., Fe $ightarrow$ ferrate, Cu $ightarrow$ cuprate, Ag $ightarrow$ argentate, Au $ightarrow$ aurate, Pb $ightarrow$ plumbate, Sn $ightarrow$ stannate).

1
Bridging Ligands: — Indicated by '$mu$-' prefix before the ligand name (e.g., $mu$-hydroxo).
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Isomers: — Geometric (cis-/trans-), optical ($Delta/Lambda$), linkage (nitrito-N/nitrito-O) prefixes are used where applicable.

Vyyuha Quick Recall

To remember the IUPAC naming order: Can Ligands Make Out Smoothly?

Cation first
Ligands (alphabetical, ignoring prefixes)
Metal
Oxidation state (Roman numeral)
Suffix ('-ate' if anionic complex)