Coordination compounds
Dr. Peter Warburton
peterw@mun.ca
http://www.chem.mun.ca/zcourses/1051.php
Complex ions
AgCl(s) + 2 NH3(aq) → [Ag(NH3)2]+(aq) + Cl-(aq)
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Theory of coordination compounds
Compounds made up
of simpler
compounds are
called coordination
compounds.
Alfred Werner
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Coordination compounds
Coordination compounds contain
complex ions which are polyatomic
cations or anions composed of:
a central metal ion and ligands
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Werner’s theory of coordination compounds
[Co(NH3)6]Cl3 and [CoCl(NH3)5]Cl2
Two compounds made of the same
chemicals, yet they look different, and
react differently with silver nitrate.
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Werner’s theory
Two types of valence or bonding capacity.
Primary valence.
Based on the number of e- an atom loses in
forming the ion.
Secondary valence.
Responsible for the bonding of other groups,
called ligands, to the central metal atom.
[Co(NH3)6]Cl3 → [Co(NH3)6]3+ + 3 Cl-
[CoCl(NH3)5]Cl2 → [CoCl(NH3)5]2+ + 2 ClAll media copyright of their respective
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Cobalt coordination compounds
In all these compounds the central cobalt
ion of the complex ion (the square
brackets) has SIX ligands around it.
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Cobalt coordination compounds
The number of nitrate groups 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
Coordination number – #
of points of attachment by
ligands to the metal ion
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Coordination sphere
Coordination sphere
– the central metal
ion and the ligands
[CoCl(NO2)(NH3)4]+
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Problem
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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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-
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Ligands
Ligands are Lewis bases –
electron pair donors.
They donate electrons to the metal
ion, which acts as a Lewis acid –
electron pair acceptor.
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Ligands
Monodentate ligands
Use one pair of electrons to form one point of
attachment to the metal ion.
Bidentate ligands
Use two pairs of electrons to form two points
of attachment to the metal ion.
Tridentate, tetradentate, …
See Tables 24.2 and 24.3
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Formulas for complex ions
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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Formulas for complexes
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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