Download 2.complex ions intro and shape

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Complex ions
N Goalby
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Complex ion formation
A complex ion is formed when a metal ion is surrounded
by ligands which are bonded by co-ordinate bonding
into the metal ion
A ligand is a molecule or negative ion which can donate a
lone pair of electrons. eg H2O, NH3, amines, Cl-, CNThe number of ligands
bonded to the metal ion is
called the co-ordination
number.
The co-ordination number
exceeds its oxidation state.
2+
OH2
H2O
H2O
Co
OH2
OH2
OH2
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COMPLEX FORMATION
Lewis base
Lewis acid
electron pair donor (ligands are Lewis bases)
electron pair acceptor
Cl
In the formation of complex
ions the ligand is the Lewis
base as it donating a pair of
electrons in the dative
covalent bond and the
metal ion is the Lewis acid
2-
Cu
Cl
Cl
Cl
Ligands form co-ordinate
bonds via lone pairs
Shapes of Complex ions: Octehedral
Most common complex ions
have a coordination number 6
(i.e six ligands). The shape is
called octahedral.
2+
OH2
H2O
H2O
Ni
OH2
OH2
OH2
[Ni(H2O)6]2+
All the bond angles are 90º
The octahedral complexes are
usually with small ligands such
as H2O and NH3
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Shapes of Complex ions: Coordination number 4
There are two shapes with a coordination number of 4
Cl
Tetrahedral complexes
are more common with
larger ligands e.g. Cl-
2-
Cu
Cl
Bond angle 109½º
Cl
Cl
Square planar
Bond angle 90º
2-
H3 N
Cl
Pt
H3 N
Cl
Occur in Pt2+ complexes
Shapes of Complex ions: linear
Linear
coordination number 2
+
H 3N
Silver commonly forms linear
complexes e.g. [Ag(NH3)2]+,
[Ag(S2O3)2]3- and [Ag(CN)2]-).
Ag
NH3
diamminesilver(I)
Bond angle 180º
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Four Common Structures Of Complex Ions
NH3
NH3
NH3
NH3
Ag+
Pt2+
NH3
NH3
Linear
Square planar
NH3
NH3
NH3
NH3
Co3+
Zn2+
NH3
NH3
NH3
NH3
NH3
NH3
Tetrahedral
Octahedral
Examples of complex ions
2+
NH3
H3 N
Ni
H3 N
NH3
NH3
NC
NC
NH3
CN
Fe
CN
CN
Hexaamminenickel(II)
Cl
Hexacyanoferrate(II)
2-
+
Cu
Cl
4-
CN
H 3N
Ag
NH3
Cl
Cl
tetraachlorocuprate(II)
diamminesilver(I)
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Ligands
Unidentate ligands
These are ligands that can form one dative covalent bond with
the metal ion. They will generally have one lone pair. eg H2O,
NH3, OH-, Cl-, CNBidentate ligands contain two donor atoms. They bond to the
metal ion through two atoms.
N
CH2 CH2 N
H
H
H
O
C
C
O
1,2-diaminoethane
NH2CH2CH2NH2
-
:
-
:
:
:
H
O
O
Ethanedioate(oxalate) ion
-
-OOC-COO-
Complexes containing bidentate ligands
3+
CH2
NH2
H 2C
NH2 CH
2
NH2
Cr
NH2
NH2
H2 C
CH2
CO2
O 2C
Cu
O
O
H
H
NH2
CH2
[Cr(NH2CH2CH2NH2)3]3+
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Multidentate Ligands
Hexadentate ligand
EDTA is a hexadentate ligand which has six
atoms that can form a dative covalent
bond.
It has a 4- charge (edta)4-
O
-O
C
O
CH2
N
-O
C
CH2
C O-
CH2
C
CH2 CH2 N
CH2
O-
O
O
EDTA
O
The EDTA4- anion has the formula
O
-O
C
-O
C
CH2
N
O
C
O
CH2
CH2
C O-
CH2
C
O
C
CH2 CH2 N
O-
CH2
CH2
N
O
CH2
Cu
O
with six donor sites(4O and 2N) and
forms a 1:1 complex with metal(II)
ions
O
O
N
C
O
As it can form six dative covalent bonds with
the metal ion, edta will only ever have a ratio of
one molecule of edta to one ion of the metal
eg [ Ni(edta)]2-
CH2
CH2
O
CH2
C
O
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Multidentate Ligands
Multidentate ligands – form several co-ordinate bonds
haem
H2C
CH3
H3C
N
N
CH2
Fe
N
H3C
N
CH3
COOH
COOH
What types of bonding are present in the following
compound containing a complex ion?
K3[Fe(CN)6]
• Ionic bonding between the potassium and the complex
ion [Fe(CN)6]3•Dative covalent bonding between the CN- ligand and the
Fe3+ ion
•Covalent bonding in the CN- ion
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Two Coordination Compounds of Co(III)
NH3
H3N
H3N
3 Cl
NH3
2+
H3N
NH3
Cr
NH3
3+
NH3
Cr
H3N
Cl
H3N
2 Cl
H3N
CoCl3.6NH3
CoCl3.5NH3
3 free Clper formula
2 free Clper formula
[Co(NH3)6]Cl3
[CoCl(NH3)5]Cl2
extra
Isomers of Cr(H2O)6Cl3
OH2
H2 O
Cr
H2 O
OH2
3+
2+
H2 O
OH2
3 Cl
OH2
OH2
Cr
Cl
2 Cl
OH2
H2O
H2 O
H2 O
Will react with Ag+ on 1:3 ratio
Will react with Ag+ on 1:2 ratio
The free Cl- ions will react with Ag+ to form AgCl (s)
OH2
H2 O
Cl
Cr
OH2
+
Cl
OH2
Cl
Cl
2H2O
H2 O
Will react with Ag+ on 1:1 ratio
H2 O
Cr
+
Cl
OH2
Cl
2H2O
H2 O
Will react with Ag+ on 1:1 ratio extra
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Isomerism In Complex Ions
Structural isomers differ in the ligands that are attached to
the central atom or in the donor atoms through which the
ligands are bonded.
Geometric isomers differ in the arrangement of the attached
ligands, forming either cis- (same side) or trans- (opposite
sides) compounds.
Optical isomers are isomers that differ in their ability to rotate
the plane of polarized light. Each of the two molecules or
ions of an optical isomer is called an enantiomer and each
enantiomer rotates the plane-polarized light in opposite
directions.
key
Geometric Isomerism In A
Square Planar Complex
2-
H3 N
H3 N
Pt
Cl
Cl
Cis-Diamminedichloroplatinum(II)
Cisplatin
2-
H3 N
Cl
Pt
Cl
NH3
trans-Diamminedichloroplatinum(II)
transplatin
key
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Geometric Isomerism In An
Octahedral Complex
NH3
+
Cl
NH3
NH3
Cr
+
Cl
NH3
Cr
Cl
NH3
NH3
Cl
NH3
NH3
Cis-[CoCl2(NH3)4]+
trans-[CoCl2(NH3)4]+
extra
Optical Isomers
mirror
CH2
CH2
NH2
H2 C
NH2
2+
NH2
NH2 CH2
Co
NH2
H2N
CH2
NH2
CH2
CH2
H2 C
CH2
NH2
2+
CH2
NH2
Co
NH2
NH2
H2N
CH2
CH2
extra
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