Complex ions
Coordination compounds
Dr. Peter Warburton
peterw@mun.ca
http://www.chem.mun.ca/zcourses/1051.php
AgCl(s) + 2 NH3(aq) → [Ag(NH3)2]+(aq) + Cl-(aq)
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Coordination compounds
Theory of coordination compounds
Coordination compounds
contain complex ions
which are polyatomic
cations or anions
composed of:
a central metal ion and
ligands
Counterions balance the
charge of the complex ion
to make the coordination
compound neutral
Compounds made up
of simpler
compounds are
called coordination
compounds.
Alfred Werner
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Werner’s theory
Werner’s theory of coordination compounds
Two types of valence or bonding capacity.
[Co(NH3)6]Cl3 and [CoCl(NH3)5]Cl2
Primary valence.
Based on the number of e- an atom loses in
forming the ion (the oxidation number of the
metal ion).
Secondary valence.
Two compounds made of the same
chemicals, yet they look different, and
react differently with silver nitrate due
to different number of counterions.
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Responsible for the bonding of other groups,
called ligands, to the central metal atom (leads
to coordination number)
In these compounds
the primary and
secondary valence
Cl- are the same!
[Co(NH3)6]Cl3 → [Co(NH3)6]3+ + 3 Cl[CoCl(NH3)5]Cl2 → [CoCl(NH3)5]2+ + 2
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Cobalt coordination compounds
Cobalt coordination compounds
In all these compounds the central cobalt
ion of the complex ion (the square
brackets) has SIX ligands around it.
The number of nitrate counterions depends
on the charge of the complex ion, which
depends on the charges of the central ion and
the ligands.
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Coordination number and shape
Coordination sphere
Coordination sphere
– the central metal
ion and the ligands
Coordination number – total
number of points of
attachment the central ion
can make with ligands
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[CoCl(NO2)(NH3)4]+
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Problem
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Problem
Write the formula of a complex ion with
cyanide ion ligands, an iron ion with an
oxidation state of +3, and a
coordination number of 6.
Answer: [Fe(CN)6]3-
What are the coordination number and
oxidation state of Ni in the complex ion
[Ni(CN)4I]3-?
Answer: The coordination number is 5.
The oxidation state of Ni is +2.
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Ligands
Ligands
Monodentate ligands
Ligands are Lewis bases –
electron pair donors.
Use one pair of electrons to form one point
of attachment to the metal ion.
Bidentate ligands
They donate electrons to the metal,
which acts as a Lewis acid –
electron pair acceptor.
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Ligands
Use two pairs of electrons to form two
points of attachment to the metal ion.
Tridentate, tetradentate, …
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Polydentate ligands
monodentate bidentate
EDTA is tetradentate
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Formulas for complex ions
Formulas for complexes
The complex ion is in square brackets!
Metal ion first
Anions next – in alphabetical order BY
CHEMICAL SYMBOL if there are more than
one kind
Neutral ligands last – in alphabetical order
BY CHEMICAL SYMBOL if there are more
than one kind
Overall charge of the complex ion outside of
brackets
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Check to see if the rules have been followed in
the complexes of these coordination compounds.
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Problem
What would the formula be for the
following complex?
Answer:
[CrBr2(H2O)2(NH3)2]+
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