Ligands and complex ions :)

Question 1

What is a complex ion?

Answer 1

A complex ion is a metal ion surrounded by coordinately bonded ligands (bonded by dative covalent bonds).

Question 2

What is a ligand

Answer 2

A ligand is an ion, atom or molecule that has a lone pair that it can use to coordinately bond to the central metal ion

Question 3

whats a monodentate ligand and give examples

Answer 3

it has only 1 lone pair and thus can form one coordinate bond to the central metal ion
examples:
:NH3
H20:
:CN-
:Cl-

Question 4

whats a bidentate ligand and give 2 examples

Answer 4

A type of multidentate ligand that can form 2 coordinate bonds to the central metal ion (has 2 lone pairs)
E.g ethane-1,2- diamine (H2NCH2CH2NH2)
Ethanedioate (C2O4^2-)

Question 5

What is the coordination number?

Answer 5

The number of coordinate bonds in a complex formed between the ligands and central metal ion. It is NOT the number of ligands.

Question 6

What are some small ligands, and how many fit around central metal ion?

Answer 6

H2O, NH3, CN-
6 can fit around central metal ion

Question 7

What are larger ligands and how many can fit around central metal ion?

Answer 7

Larger: Cl- (4 can fit around central metal ion)
Even larger: bidentate ligands ethanedioate and ethane-1,2-diamine (3 can fit around central metal ion)

Question 8

Whats the shape of the complex and bond angle when the coordination number is 6?

Answer 8

Octahedral
bond angle: 90 degrees

Question 9

Whats the shape of the complex when the coordination number is 4?

Answer 9

Tetrahedral (109.5 degree bond angle)
OR Square planar (90 degrees)

Question 10

What is optical isomerism? What type of complex forms optical isomers? Whats another word for optical isomers, and what can optical isomers do?

Answer 10

A type of stereoisomerism where the molecules have the same structural formula but the bonds have a different orientation in space.
When an ion can exist as two non-superimposable mirror images, optical isomers form for complex ions.

Optical isomers form in an octahedral complex where there are 3 bidentate ligands around the central metal ion, and they are non-superimposable mirror images of each other.

Each non-superimposable mirror image is can be called an enantiomer
Optical isomers rotate plane polarised light

Question 11

Give an example of a square planar complex and its use (including pros and cons of it) and how it works

Answer 11

Cis-Platin [pt(NH3)2Cl2] (aq)
2 ammonia ligands 2 chloride ligands and central platinum ion
Used as an anti-cancer drug. Works because the chloride ions can easily be displaced so they detach from the complex and bind to the nitrogen on the DNA of cancer cells. This prevents cancer cells from replicating and causes them to die
Cons: can stop healthy cells from replicating, weakening the immune system and causing kidney damage.

Question 12

What complexes display cis-trans isomerism and what is it

Answer 12

Cis-trans isomerism can happen in octahedral complexes where there is 4 of the same type of ligand and 2 ligands of a different type. When the ligands of a different type are opposite each other (e.g one at top and one at bottom) this is TRANS isomerism. When the 2 ligands of a different type are adjacent to each other, CIS isomerism.
It occurs in square planar as well with 2 ligands of the same type and 2 ligands of a different type. When the ligands of a different type are on opposite sides, TRANS isomerism. When they are adjacent/on the same side of the molecule, CIS isomerism.

Question 13

What is the structure of haemoglobin?

Answer 13

Haemoglobin has an octahedral structure. It has a central Fe2+ (iron) ion. On the top it contains either a water molecule or an oxygen molecule bound to the Fe2+ ion. On the bottom of the complex, a Nitrogen (N) is bound to the central ion (Fe2+) and this nitrogen is part of a protein called globin. The middle of the complex consists of four (N) nitrogen atoms bound to the iron ion. This nitrogen atoms form a ring around the complex and this ring is called the haem group.

Question 14

How does haemoglobin carry out its function? And what is its function?

Answer 14

Haemoglobin is a protein found inside red blood cells that carries oxygen from the lungs to the tissues. In the lungs, the complex substitutes it’s water molecule for oxygen and becomes oxyhaemoglobin. At the tissues, the oxygen is delivered to the cells for respiration and swapped for a water ligand (which is then removed, i.e via exhalation)

Question 15

How does carbon monoxide poisoning happen?

Answer 15

When carbon monoxide is inhaled, The water ligand bound to the complex is swapped with the CO ligand, which binds to the complex. The CO ligand forms a very strong coordinate bond to the central metal ion and does not readily exchange with oxygen or water. This means oxygen can no longer bind to the complex, causing oxygen starvation. Lack of oxygen causes dizziness, unconsciousness or death.

Question 16

Whats a ligand substitution reaction?

Answer 16

When a ligand is substituted for another ligand.

Question 17

What happens if ligands of similar size are substituted?

Answer 17

If they are similar sized ligands (e.g. NH3 and H2O ligands), there is no change in coordination number or shape or the complex because the same amount of ligands can fit around the central metal ion.
However there will be a colour change as it is still a different ligand

Question 18

What happens if different sized ligands substitute?

Answer 18

Then there will be a change in the complex’s shape, as a different amount of ligands can fit around the central ion. There is also a change in coordination number (which results in the change of the shape of the complex). There will also be a colour change.

Question 19

What is partial ligand substitution?

Answer 19

Sometimes not all the water molecules are exchanged for a different ligand, some still remain.
E.g.
[Cu(H2O)6]^+2(aq) +4NH3(aq)–> [Cu(NH3)4(H2O)2]^+2 (aq)+6H20 (l)
Shape is still octahedral (since NH3 and H2O are similar sized ligands) but there is a colour change from blue to dark blue