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Ligands and Complex Ions Chemistry Tutorial

Key Concepts

  1. Anionic ligands have names ending in 'o'.

    ⚛ 'ide' → 'o', eg, chloride → chloro

    ⚛ 'ate' → 'ato', eg, sulfate → sulfato

  2. Neutral ligands are named as the molecule with these notable exceptions:

    ⚛ H2O → aquo

    ⚛ NH3 → ammine

    ⚛ CO → carbonyl

  3. The numbers of ligands in a complex are specified using the Greek prefixes:

    ⚛ di for 2

    ⚛ tri for 3

    ⚛ tetra for 4

    ⚛ penta for 5

    ⚛ hexa for 6

  4. The name of a cationic complex ion ends in the name of the central metal ion with the oxidation state shown as a Roman numeral in parantheses at the end of the metal's name, eg, iron(III).
  5. The name of an anionic complex ion ends in 'ate',
    ⚛ chromium(II) → chromate(II)
    ⚛ nickel(II) → nickelate(II)
    ⚛ platinum(II) → platinate(II)

    sometimes the latin name is used, eg,
    ⚛ silver(I) → argentate(I)
    ⚛ iron(II) → ferrate(II)
    ⚛ copper(I) → cuprate(I)
    ⚛ lead(II) → plumbate(II)
    ⚛ gold(I) → aurate(I)
    ⚛ tin(IV) → stannate(IV)

  6. Ligands are named before the central metal atom.

  1. Identify the central metal ion
  2. Identify the charge on the central metal ion (shown in parantheses)
  3. Identify the ligands
  4. Identify the number of ligands
  5. Calculate the total charge on the ligands
  6. Calculate the charge on the complex ion
        = charge on metal ion + total charge on ligands
  7. Write the formula giving the central metal ion first followed by the ligands,
    for example, Mn(H2O)62+
  8. If more than one type of ligand is present, anion ligands are given before neutral ligands,
    for example, CrCl2(NH3)4+

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Common Ligands

Ligands can be:

The table below lists some common polar molecules which can be present as ligands:

Polar Compound Name Formula Ligand Name Bonding Atom
water H2O aquo O
carbon monoxide CO carbonyl C
ammonia NH3 ammine N

The table below lists some anions which can be present as ligands:

Ion Name Formula Ligand Name Bonding Atom
chloride Cl- chloro Cl
fluoride F- fluoro F
bromide Br- bromo Br
iodide I- iodo I
cyanide CN- cyano C
hydroxide OH- hydroxo O
thiosulfate S2O32- thiosulfato O
carbonate CO32- carbonato O and O
oxalate C2O42- oxalato O and O

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Naming Complex Ions

Example: Name the complex ion with the forumla Fe(CN)63-

  1. Anionic ligands have names ending in 'o'.
    CN- (cyanide ion) named as cyano
  2. The numbers of ligands in a complex are specified using a Greek prefix:
    6 ligands = hexa → hexacyano
  3. Oxidation state of the central metal atom is shown with a Roman numeral in parantheses at the end of the metal's name:
    Central metal ion is iron
        Charge on iron: 3- = x + (6 × 1-)
        3- = x -6
        x = 3+
    Central metal ion: iron(III)
  4. The complex ion is an anion, therefore the name will end in ferrate(III)
  5. Ligands are named before central metal ion: hexacyanoferrate(III)

Examples of Names of Complex Ions

Formula Ligand
Name
No. of Ligands
and prefix
Central Ion
Name
Complex Ion Name
Ag(NH3)2+ ammine 2di silver(I)
+1= x + 2(0)
x = +1
diamminesilver(I) ion
(complex is a cation)

Ag(CN)2- cyano 2di silver(I) → argentate(I)
-1 = × + 2(-1)
x = +1
dicyanoargentate(I) ion
(complex is an anion)

Cu(H2O)62+ aquo 6hexa copper(II)
+2 = x + 6(0)
x = +2
hexaaquocopper(II) ion
(complex is a cation)

CuCl42- chloro 4tetra copper(II) → cuprate(II)
-2 = x + 4(-1)
x = +2
tetrachlorocuprate(II) ion
(complex is an anion)

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Writing the Formula of Complex Ions

Example: write the formula for the complex ion tetraamminecopper(II)

  1. Identify the central metal ion :
    copper, Cu
  2. Identify the charge on the central metal ion (shown in parantheses):
    2+
  3. Identify the ligands:
    ammine = NH3 (neutral species, charge on ligand = 0)
  4. Identify the number of ligands:
    tetra = 4
  5. Calculate the total charge on the ligands:
    = 4 × 0 = 0
  6. Calculate the charge on the complex ion
    = charge on metal ion + total charge on ligands = 2+ + 0 = 2+
  7. Write the formula giving the central metal ion first followed by the ligands :
    Cu(NH3)42+

Examples of Formulae of Complex Ions

Name Central Ion
Formula
Ligand
Formula
No. of
Ligands
Complex Ion
Formula
hexaaquocobalt(II) ion Co2+
(charge in parentheses)
H2O
(aquo = H2O)
hexa = 6 Co(H2O)62+
(4 × 0 +2 = +2)

tetrachlorocobaltate(II) ion
(ate = anion)
Co2+
(charge in parentheses)
Cl-
(chloro = Cl-)
tetra = 4 CoCl42-
(4 × -1 + 2 = -2)

tetracarbonylnickel(II) ion Ni2+
(charge in parentheses)
CO
(carbonyl = CO)
tetra = 4 Ni(CO)42+
(4 × 0 + 2 = +2)

tetracyanonickelate(II) ion
(ate = anion)
Ni2+
(charge in parentheses)
CN-
(cyano = CN-)
tetra = 4 Ni(CN)42-
(4 × -1 +2 = -2)

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Shapes (Geometry) of Some Complex Ions

Examples of the Shapes of Some Complex Ions

The shape, or geometry, of a number of complex ions is given in the table below:

Complex Ion Formula No. of Ligands Coordination Number Shape
(Geometry)
Ag(NH3)2+ 2 2 linear
CuCl2- 2 2 linear
Cr(NH3)63+ 6 6 octahedral
Fe(CN)63- 6 6 octahedral

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