Stability constants

Question 1

What is a lewis base?

Answer 1

Ligand

Electron pair donor

Question 2

What is a lewis acid?

Answer 2

Metal

Electron pair acceptor

Question 3

What is binding affinity expressed as?

Answer 3

A numerical value

Question 4

What is kinetic stability?

Answer 4

The rate of reaction

Whether something is labile or inert

Question 5

What is thermodynamic stability?

Answer 5

The position of equilibrium which is measured using the equilibrium constant

Question 6

Is there a correlation between kinetic and thermodynamic stability?

Answer 6

No

Question 7

What is used to show kinetic stability?

Answer 7

small k

Question 8

What is used to show thermodynamic stability?

Answer 8

large K

Question 9

What do you measure the thermodynamic affinity of?

Answer 9

the ligand binding to the metal

Question 10

What equation is used to calculate K?

Answer 10

K = [Products]/[reactants]

Question 11

What is the binding of the ligand like when the value of K is large?

Answer 11

Tight binding

Question 12

What is the binding of the ligand like when the value of K is small?

Answer 12

Weak binding

Question 13

What value of K is favoured?

Answer 13

Large value of K

Question 14

Due to stability constants usually being large, what is the more convenient way to measure them?

Answer 14

Use Log10(K)

Question 15

What does K not tell you anything about?

Answer 15

Rate
There is no relationship to the rate of reaction
A large K does not mean ligands bind fast

Question 16

What symbol is used for the formation constant?

Answer 16

β

Question 17

What would the general equation for K1 be?

Answer 17

K1 = [MLⁿ⁺] / [Mⁿ⁺][L]

Question 18

What would the general equation for K2 be?

Answer 18

K2 = [ML₂ⁿ⁺]/[MLⁿ⁺][L]

Question 19

What would the general formation constant be?

Answer 19

β = [ML₂ⁿ⁺]/[Mⁿ⁺][L]²

Question 20

How would you generate the formation constant?

Answer 20

Look at the starting and end concentrations and the amount of ligands used
Intermediates aren’t included

Question 21

If you expand the formation constant, what can you get?

Answer 21

The two K constants generated

β = K1 x K2

Question 22

What is the general order for the values of the stability constants?

Answer 22

K1>K2>K3>K4

Question 23

What are the three influencing factors for the value of β?

Answer 23

1) Sterics
2) Statistics
3) charge

Question 24

Which factor is the most important?

Answer 24

Sterics

Question 25

How do sterics effect β?

Answer 25

When you substitute a new ligand its usually bigger than the ligands that are already bound This means if any more are added, they will be repelled by the larger ligand already substituted. The repulsion causes the reaction to become more difficult

Question 26

What are statistics and how do they influence β?

Answer 26

As more ligands bind, this reduces the amount of variable sites available for the new ligands to bind

Question 27

When is charge a problem and effects β?

Answer 27

When anionic ligands are used

Question 28

What happens when you add 3 charged ligands to a positive complex?

Answer 28

The first one - Attracted to the complex to binds easily The second one - binding to a neutral complex so there is no charge issue The third one - binding to a negatively charged complex meaning that the anion will be repelled

Question 29

Which metal is an exception, having an unfavourable change in co-ordination number? Explain.

Answer 29

Hg | When a third ligand is added, K3 is low and K4 is high which doesn't follow the trend

Question 30

What is the order for K values for spin states when adding large ligands such as bipy and phen?

Answer 30

K1>K2

Question 31

What is a chelate ring?

Answer 31

Ring made up of ligands, usually bidentate

Question 32

Why are chelate rings preferred?

Answer 32

They are more stable | Bidentate ligands bind tigheter to a metal than two similar monodentate ligands

Question 33

How do formation constants for bidentante ligands compare to monodentant ligands?

Answer 33

They are significantly larger

Question 34

How does the dissociation of monodentate ligands compare to the dissociation of bidentate ligands?

Answer 34

Monodentate ligands dissociation from the metal ion For bidentate, the dissociated end cannot migrate away from metal ion. Migration requires simultaneous breaking of two bonds which is very unlikely

Question 35

How does the entropy of monodentate ligands compare to the entropy of bidentate ligands?

Answer 35

There is higher disorder and higher entropy for a reaction with bidentante ligands 2 molecules to 3 whereas monodentate ligands are 3 to 3

Question 36

What is the macrocyclic effect?

Answer 36

Multidentate ligands binding to one metal

Question 37

What are crown ethers?

Answer 37

Multiple oxygens joined to the metal centre | Different metals match different cavity sizes

Question 38

How is the best fit for a crown ether determined?

Answer 38

Highest K value

Question 39

What is the chelate effect mostly?

Answer 39

Entropic in nature