Transition Metals
& Complex ions
• State and give examples of complexes with six-fold
coordination with an octahedral shape
• Describe and use the terms: complex ion and
coordination number.
• Explain the term ligand in terms of coordinate bonding.
Definition Hangman – Coordinate bond
(aka – dative covalent bond)
_A/ shared
_ _ _ _ _ pair
_ / _ _of_ electrons
_ / _ _ / _ _ in
_ _which
_____
/the
_ _ /bonded
_ _ _ _ _ pair
/ _ _ _has
/ _ been
_ _ _ _ provided
_/____/
___/____/________/__/___/
by one of the bonding atoms only.
_ _ / _ _ _ / _ _ _ _ _ _ _ / _ _ _ _ _ / _ _ _ _.
Complex ion [Fe(H2O)6]2+
Each of the six H2O
ligands forms one
coordinate (dative
covalent) bond to the
central metal ion
using a lone pair of
electrons from its
oxygen atom.
This complex ion has a coordination number of six
(the number of coordinate bonds to the central metal ion)
Charges on complex ions
The overall charge of a complex ion is the sum of the individual
charges of the transition metal ion and those of the ligands.
Name of
ligand
Formula
Charge
Water
:OH2
None - neutral
Ammonia
Thiocyanate
:NH3
:SCN-
None - neutral
-1
Cyanide
:CN-
-1
Chloride
Hydroxide
:Cl:OH-
-1
-1
Example
State the formula and
charge of the complex ion
made from one Iron (II) ion
and 6 cyanide molecules.
[Fe(CN)6]4-
All of these ligands are classed as monodentate ligands
(i.e. They only donate one pair of electrons to the central metal ion)
Formulae Questions
1. State the formula & charge of each of these complex ions:
a) One copper (II) ion & four chloride ions
b) One iron (III) ion & five water molecules & a chloride ion.
c) One copper (II) ion & four ammonia molecules & two hydroxide
ions
d) One cobalt (III) ion & four hydroxide ions
2. What is the oxidation number of the transition metal in
each of these complex ions.
a)
b)
c)
d)
[Fe(CN)6]3[Co(SCN)4]2[Cu(CN)4(Cl)2]4[Ti(H2O)3OH]2+
3D shapes of complex ions
Most common shape = octahedral
( 6 coordinate bonds)
BOND ANGLE = all 90o
3D shapes of complex ions
Less common shape = tetrahedral
( 4 coordinate bonds)
BOND ANGLE = all 109.5o
The copper(II)
and cobalt(II)
ions have four
chloride ions
bonded to them
rather than six,
because the
chloride ions are
too big to fit any
more around the
central metal ion.
Shapes of complex ions Questions
For each of the 8 complex ions you worked
with during “formulae questions” draw the
3D shape using the wedge shaped bonds,
show the bond angles and name the shape.
Reminder – what is a
stereoisomer?
• Molecules or complexes with the
same structural formula but with a
different arrangement of the atoms
in space.
Stereoisomerism in complex ions
Cis–trans isomerism in [Co(NH3)4Cl2]+
Chloride
ligands at
90o to each
other
Chloride
ligands at
180o to each
other
Stereoisomerism in complex ions
Cis–trans isomerism in [NiCl2(NH3)2]
4 coordinate bonds – alternative to tetrahedral
= Square Planar
BOND ANGLE = all 90o
Structure of cis-platin
Effective cancer
treatment –
Thought to bind to
and alter cancer cell
DNA and therefore
prevent their growth
and reproduction
1. What is the formula for cis-platin?
2. Explain why this molecule uses the prefix “cis” in its name.