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Coordination Compounds - IUPAC nomenclature

Grade 12ICSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The cation is always named first, followed by the naming of the anion, regardless of whether the coordination entity is positively or negatively charged.

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When naming the coordination sphere, ligands are listed in alphabetical order before the name of the central metal atom or ion.

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Anionic ligands end in the letter −o-o. For example: Cl−Cl^- (chlorido), CN−CN^- (cyanido), OH−OH^- (hydroxido), and C2O42−C_2O_4^{2-} (oxalato).

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Neutral ligands generally keep their molecular names, with specific exceptions: H2OH_2O is called 'aqua', NH3NH_3 is 'ammine', COCO is 'carbonyl', and NONO is 'nitrosyl'.

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Prefixes such as di−di-, tri−tri-, tetra−tetra- are used to indicate the number of individual ligands. If the ligand name itself includes a numerical prefix (e.g., ethane-1,2-diamine), the prefixes bis−bis-, tris−tris-, tetrakis−tetrakis- are used, and the ligand name is placed in parentheses.

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The oxidation state of the central metal is indicated by a Roman numeral in parentheses (e.g., (II), (III)) immediately following the metal name.

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In anionic coordination entities, the name of the central metal ends with the suffix −ate-ate. For example, FeFe becomes ferrate, CuCu becomes cuprate, and AgAg becomes argentate. In neutral or cationic complexes, the metal name remains unchanged.

📐Formulae

Oxidation Number of Metal(x)+∑Charges of Ligands=Net Charge of Coordination Sphere\text{Oxidation Number of Metal} (x) + \sum \text{Charges of Ligands} = \text{Net Charge of Coordination Sphere}

Coordination Number (C.N.)=Number of Ligands×Denticity\text{Coordination Number (C.N.)} = \text{Number of Ligands} \times \text{Denticity}

Effective Atomic Number (EAN)=Z−(Oxidation State)+2×(Coordination Number)\text{Effective Atomic Number (EAN)} = Z - (\text{Oxidation State}) + 2 \times (\text{Coordination Number})

💡Examples

Problem 1:

Give the IUPAC name of [Co(NH3)5(CO3)]Cl[Co(NH_3)_5(CO_3)]Cl.

Solution:

Pentaamminecarbonatocobalt(III) chloride

Explanation:

The complex is a cation. Ligands are ammine (NH3NH_3) and carbonato (CO32−CO_3^{2-}). Alphabetically, ammine comes first. Oxidation state of CoCo: x+5(0)+1(−2)=+1x + 5(0) + 1(-2) = +1 (charge of counter ion Cl−Cl^- is −1-1), so x−2=1⇒x=+3x - 2 = 1 \Rightarrow x = +3.

Problem 2:

Write the IUPAC name for K2[Zn(OH)4]K_2[Zn(OH)_4].

Solution:

Potassium tetrahydroxozincate(II)

Explanation:

Potassium is the cation. The complex [Zn(OH)4]2−[Zn(OH)_4]^{2-} is the anion, so the metal name ends in −ate-ate (zincate). Oxidation state of ZnZn: 2(+1)+x+4(−1)=0⇒2+x−4=0⇒x=+22(+1) + x + 4(-1) = 0 \Rightarrow 2 + x - 4 = 0 \Rightarrow x = +2.

Problem 3:

What is the IUPAC name of [Pt(NH3)2Cl(NO2)][Pt(NH_3)_2Cl(NO_2)]?

Solution:

Diamminechloridonitrito-N-platinum(II)

Explanation:

This is a neutral complex. Ligands are ammine, chlorido, and nitrito-N (linked via NN). Alphabetical order: ammine, chlorido, nitrito. Oxidation state of PtPt: x+2(0)+1(−1)+1(−1)=0⇒x=+2x + 2(0) + 1(-1) + 1(-1) = 0 \Rightarrow x = +2.

Problem 4:

Write the formula for Iron(III) hexacyanidoferrate(II).

Solution:

Fe4[Fe(CN)6]3Fe_4[Fe(CN)_6]_3

Explanation:

The cation is Fe3+Fe^{3+}. The anion is hexacyanidoferrate(II), which is [Fe(CN)6]4−[Fe(CN)_6]^{4-} (since x+6(−1)=−4⇒x=+2x + 6(-1) = -4 \Rightarrow x = +2). To balance the charges +3+3 and −4-4, we use the cross-over method to get Fe4[Fe(CN)6]3Fe_4[Fe(CN)_6]_3.