TRANSITION METALS Flashcards
What is a ligand substitution reaction?
Where one ligand can be swapped for another ligand
During a ligand sibstitution reaction, what must happen to ensure that both the coordination number and shape stay the same?
The ligands must be of similar size, e.g water and ammonia
Give the similarities between ammonia and water ligands:
similar size and uncharged so they can be exchanged with each other without any change in co-ordination number or shape
What does a ligand substitution reaction always result in, no matter the size of the ligand?
A colour change
Give an equation representing a ligand substitution reaction where [Co(H20)6] 2+ reacts with an excess of ammonia:
[Co(H20)6] 2+ + 6NH3 –> [Co(NH3)6] 2+ + 6H20
Give the coordination number change, the shape and the colour change of the conversion of [Co(H20)6] 2+ INTO [Co(NH3)6] 2+
Goes from pink to straw coloured
Shape remains octahedral
Coordination number remains as 6.
THERE IS ALWAYS A COLOUR CHANGE WHEN THERE IS A CHANGE IN LIGAND
If the ligands are different sizes to each other e.g. Cl- is bigger than NH3/H20, then what changes?
There is a change in coordination number and shape
Give the colour change, the shape and the coordination numbers for the conversion of [Cu(H20)6]2+ INTO [CuCl4]2- :
Goes from octahedral to tetrahedral
Coordination number goes from 6 to 4
Colour change from pale blue to yellow-green
What is the equation for the reaction between a copper-aqua ion and 4Cl- ligands?
[Cu(H20)6]2+ + 4Cl- –> 6H20 + [CuCl4]2-
Give an example of a partial substitution reaction:
[Cu(H20)6]2+ + 4NH3 –> [Cu(NH3)4(H20)2] 2+ + 4H20
What is the shape change, the coordination number and colour change for the partial substitution reaction: [Cu(H20)6]2+ + 4NH3 –> [Cu(NH3)4(H20)2] 2+ + 4H20
Octahedral to elongated octahedral
Pale blue to deep blue
Coordination number remains 6
What is haemoglobin and what does it do?
A proteins found in the blood which helps to transport oxygen around the body
What transition metal ion does haemoglobin contain?
Fe2+
Fe2+ ions are hexa-co-ordinated. What does that mean?
Six lone pairs are donated to them to form 6 co-ordinate bonds
Haem is part of the haemoglobin molecule, what is the haem group made up of?
Four of the lone pairs which are donated to the Fe2+ come from the nitrogen atoms which forms a circle around the Fe2+ - THIS IS CALLED HAEM
In haemoglobin, what molecule is the nitrogen atom a part of?
They are part of a multidentate ligand called porphyrin
Apart from haem, what are the other parts that make up haemoglobin?
Either an oxygen or water molecule also bind to the Fe2+ ion - to form an octahedral structure
AND a protein called globin also makes up the structre of haemoglobin
How does oxygen get transported around the body with the use of haemoglobin? Describe the role of water in this as well:
Both oxygen and water will bind to Fe2+ as ligands so the complex can transport oxygen to where it is needed and then swap for H20
Describe the what happens IN THE LUNGS concerning haemoglobin:
O2 conc is high in lungs so water ligands are substituted for O2 to form oxyhaemoglobin which is carried around the body in blood.
When oxyhaemoglobin gets to a place where oxygen is needed - oxygen molecules are exchanged for water molecules
The haemoglobin returns to the lungs and the process starts again.
Describe what happens during carbon monoxide poisoning:
When CO is inhaled, haemoglobin can substitute its water ligands for CO ligands instead of O2 ligands and it forms carboxyhaemoglobin
Why does carbon monoxide poisoning occur?
CO forms a very strong bond with Fe2+ ions and doesn’t readily exchange with oxygen or water ligands. The haemoglobin can’t transport oxygen anymore.
What does CO poisoning do and what are the symptoms?
It starves the organs of oxygen - causes headaches, dizziness, unconsciousness and death
What is the haemoglobin molecule called when oxygen is bonded to it?
Oxyhaemoglobin
What is the haemoglobin molecule called when water has displaced the oxygen ligand?
Deoxyhaemoglobin
What makes a complex ion more stable than another?
If the new ligands form stronger bonds with the central metal ion - the change is less easy to reverse
Normally, ligand substitution reactions can be easily reversed, give one reason why this might not be possible?
UNLESS the new complex ion is much more stable than the previous one
Give an example showing different complex ion stabilities:
CN- ions form stronger coordinate bonds than water molecules do with Fe3+
So the complex formed with CN- ions will be more stable than the one formed with H20 ligands
So the substitution of water molecules with CN- ions in an iron(III) complex IS HARD TO REVERSE
Give the equation for the substitution of water molecules for CN- ions in an Fe3+ complex:
[Fe(H20)6]3+ + 6CN- –> [Fe(CN)6]3+ + 6H20
What type of ligand forms a more stable complex ion?
Multidentate form more stable complexes than monodentate ligands
Reactions involving what two types of ligands, are hard to reverse?
Reactions involving multidentate and bidentate ligands are hard to reverse
Give an example that shows how type of ligands affects the stability of the complex ion formed:
Complexes that contain the bidentate ligand ‘ethane-1,2-diamine’ are more stable than those that contain water molecule ligands
So, reactions where water molecules are substituted by ethane-1,2-diamine, are HARD TO REVERSE
In terms of bonds, what does a ligand exchange/substitution reaction contain?
Bonds being broken and formed
Why is the enthalpy change for a ligand substitution reaction usually very small?
Because the strength of the bonds being broken is often very similar to the bonds being made
Give an example of a ligand sub reaction that has a small enthalpy change:
Substituting ammonia with ethane-1,2-diamine in a nickel complex
Is the substitution of ammonia with ethane-1,2-diamine in a nickel complex reversible or irreversible?
It is actually REVERSIBLE but because the equilibrium lies so far to the right, it is thought of as being IRREVERSIBLE
Describe the entropy change for when a monodentate ligand is substituted by a bi/multidentate ligand? And why this happens?
The number of particles increases so there is an increase in entropy
MORE PARTICLES = GREATER ENTROPY
What reactions are MORE LIKELY to occur in terms of entropy? What does this mean in terms of complex ion stability?
Reactions that result in an increase in entropy are more likely to occur.
This is why multidentate ligands always form much more stable complex ions than monodentate ligands.
What is the chelate effect?
When a multidentate forms one coordinate bond with the central ion compared to two monodentate molecules forming two coordinate bonds with the central metal ion. The complex containing the multidentate always form much more stable complex ions
State whether there was an increase/decrease/no change in entropy here:
[Ni(NH3)6]2+ + 3NH2CH2CH2NH2 –> [Ni(NH2CH2CH2NH2)3]2+ + 6H3
There is an increase in entropy as there was 4 molecules and an increase to 7 molecules
So the more stable molecule is the one that has been formed [Ni(CH2NH2NH2CH2)3]2+
What else can replace mono/bidentate ligands to make the complex more stable?
When the hexadentate ligand EDTA4- replaces the mono/bidentate ligands, the complex formed is much more stable so the reaction is DIFFICULT TO REVERSE
Why is the reaction difficult to reverse when you are replacing mono/bidentate ligands with EDTA4-?
Because reversing them would cause a decrease in the system’s entropy
Give an equation showing the substitution of mono/bidentate ligands for hexadentate ligands such as EDTA4-:
[Cr(NH3)6]3+ + EDTA4- –> [Cr(EDTA)]- + 6NH3
Describe the change in entropy for this reaction: [Cr(NH3)6]3+ + EDTA4- –> [Cr(EDTA)]- + 6NH3
From 2 molecules to 7 molecules so entropy increases and therefore the [Cr(EDTA)]- molecule is much more stable
What is the chelate effect due to?
Both enthalpy and entropy
What can transition metals form more than one type of? What is different in each of these?
More than one type of ions and in different ions they have different oxidation states
What is a redox reaction?
When you switch between oxidation states
How many oxidation states can vanadium exist in?
4
What are vanadiums different oxidation states?
+2 , +3 , +4 , +5
When vanadium has the oxidation state, +5, what is the formula of the ion and the colour of the ion?
VO2 (+) YELLOW
When vanadium has the oxidation state, +4, what is the formula of the ion and the colour of the ion?
VO (2+) BLUE