Complex Ions - PowerPoint Presentation

Slide1

Complex Ions

A ligand is a species that can donate one or more lone pairs of electrons to form a coordinate bond with a central metal ion.

A central metal ion surrounded by ligands.

This is the

hexaquacopper(II) complex ion.

The water molecules are acting as ligands – specifically unidentate ligands, as each water is donating one lone pair of electrons in order to form a coordinate bond.

LigandNo. coordinate bondsExamplesUnidentate1H2O, NH3, Cl-, CN-Bidentate 21,2 diaminoethane NH2CH2CH2NH2Ethandioate C2O42-Hexadentate6EDTA4-

The coordination number of a complex is the coordinate bonds formed to the central metal cation in the complex ion. So, for hexaquacopper(II), it is 6.

The molecule shape above is octahedral, with a bond angle of 90 degrees. Octahedral molecules have a coordination number of 6.

A bidentate ligand donates 2 lone pairs of electrons to form 2 coordinate bonds with a central metal ion.

A

hexadentate

ligand

donates 6 lone pairs of electrons to form 6 coordinate bonds with a central metal ion. Slide2

Unidentate Ligand

Complex Shape & Bond AngleCoordination Number Water

[Cu(H20)6]2+Octahedral 906Ammonia

[Co(NH3)4(H2

0)2]2+Octahedral 90

6Chloride ion [Cu(

Cl)4]2-Tetrahedral 109.54Ammonia/Chloride[Pt(NH3)2(Cl)2]Square Planar 904Cyanide-[Cu(CN)4]2-Tetrahedral 109.54Cyanide, CN-[Ni(CN)4]2-Square Planar 904

Examples of Bidentate

Ligands

Ethanedioate (oxalate) C

2

O

4

2-

Ethanedioate is able to form

2 coordinate bonds

with the metal ion by donating 2 lone pairs of electrons (from oxygen atoms).

!,2-diaminoethane (ethylenediamine) NH

2

CH2CH2NH2

Etylenediamine

is able to form

2 coordinate bonds

with the metal ion by donating 2 lone pairs of electrons (form nitrogen atoms).Slide3

Stereoisomerism

Stereoisomers have the same structural formula but they have a different spatial arrangement of their atoms.

Cis isomer: unidentate ligands are 90° apart. Trans isomer:

unidentate ligands are 180 ° apart.

This is an example of stereoisomerism in a square planar complex. In the

cis-isomer, the two Cl unidentate ligands are separated by 90. In the trans-isomer, the Cl unidentate ligands are separated by 180.

Cis TransCis platin is used as an anti-cancer drug. It prevents the division of cancer cells by binding to the DNA, and ultimately causes apoptosis – programmed cell death. Optical IsomerismOptical isomers are stereoisomers that are non-superimposable mirror images of each other (also called enantiomers). Slide4

Ligand Substitution Reactions

[Cu(H20)6]2+ + 4Cl

-  [Cu(Cl)4]2- + 6H

2OChange in colour from blue to yellow/green

Change in coordination number from 6 to 4: shape from octahedral to tetrahedralChange in charge as chloride ions are negative.

[Cu(H20)6]2+ + 4NH3

 [Cu(NH3)4 (H20)2]2+ + 4H2OChange in colour from blue to dark blueNo change in coordination number No change in charge[Co(H20)6]2+ + 4Cl-  [Co(Cl)4]2- + 6H2O

Change in colour from pink to blueChange in coordination number from 6 to 4: shape from octahedral to tetrahedralChange in charge as chloride ions are negative. Slide5

Haemoglobin

The haem molecule consists of a porphyrin

ring that forms four coordinate bonds with an iron (II) ion. The globin protein forms a fifth coordinate bond with the iron (II) ion. Oxygen molecules bind to the Fe2+ ion in the vacant 6th

position of the octahedral complex. The binding of the O2 is weak enough to allow it to be removed easily.

Carbon monoxide, CO, bonds to haemoglobin with a higher affinity than oxygen. If a person inhales CO, a ligand exchange reaction occurs and the CO prevents the transport of O2. This leads to drowsiness, lack of consciousness and can be fatal.

Globin Protein

O2