Coordination compounds

Dr. Peter Warburtonpeterw@mun.cahttp://www.chem.mun.ca/zcourses/1051.php

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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

[Co(NH3)6]Cl3 → [Co(NH3)6]3+ + 3 Cl-

[CoCl(NH3)5]Cl2 → [CoCl(NH3)5]2+ + 2 Cl-

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.

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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 ligandsUse one pair of electrons to form one point of

attachment to the metal ion.

Bidentate ligandsUse 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 kindNeutral 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]+