Benniston

Question 1

What 3 types of reactions are there at the octahedral site

Answer 1

Ligand substitution
Electron transfer
Activation of ligands

Question 2

What is ligand stubstitution

Answer 2

Addition or removal of ligands

Question 3

What do we need to consider when looking at ligand substitution

Answer 3

Does the ligand that is being replaced simply fall off or does the new ligand associate with the complex first? How fast is the ligand replaced and does the surrounding solvent molecule have a part to play in the reaction?

Question 4

What is electron transfer

Answer 4

Change in oxidation state of the metal centre

Question 5

What do we need to consider when looking at electron transfer

Answer 5

Most metals have more than one oxidation state and so we can think about electron transfer at the metal site?

Question 6

What do we mean by activation of ligands

Answer 6

Attack at a ligand

Question 7

What do we need to consider when looking at activation of ligands

Answer 7

Since a ligand uses a lone pair of electrons to bind to a metal does this donation activate the ligand in any way

Question 8

What is a mechanism and how do we determine a mechanism

Answer 8

A mechanism describes all the pathways in which a reactant is converted to a product

Question 9

If a reaction goes by one pathway what would we need to know?

Answer 9

• how the reactant’s ground state get activated
• the structure of a defined intermediate
• how the intermediate goes to the product

Question 10

When do problems arise for a mechanism

Answer 10

When we get more than one pathway

Question 11

What conditions are probing of inorganic reactions done under

Answer 11

Pseudo first order conditions

Question 12

How do we probe mechanisms

Answer 12

One way of probing mechanisms is through the rate law, by running kinetic experiments and determining the rate law

Question 13

What does the kinetic information from probing mechanisms tell us

Answer 13

• the number and type of each molecule participating in the formation of the transition state
• the rate constant

Question 14

How could we use the eyring equation to describe reaction mechanisms

Answer 14

The rate of a reaction can be measured over a temperature range and related to parameters in the eyring equation. By rearranging the equation we can plot a graph that should be a straight line. Any deviation from this straight line tells us that there is something odd going on in the reaction

Question 15

What is KB in the eyring equation

Answer 15

boltzmann’s constant

Question 16

What is h in the eyring equation

Answer 16

Planks constants

Question 17

Draw a basic energy reaction pathway for a metal reacting with a ligand

Answer 17

see flash card

Question 18

How can we relate the free energy change of the reaction

Answer 18

we can relate this to the free energy of activation for the forward and the reverse reaction
∆Gr‡ = ∆Gf‡ + (-∆G)

Question 19

What is the equation for ∆G

Answer 19

∆G = -RTlnK

Question 20

What is the equation for ∆Gf
Where f means forward

Answer 20

∆Gf‡ = ∆Hf‡ - T∆Sf

Question 21

What is the equation for ∆Gr
Where r is the forward reaction

Answer 21

∆Gr‡ = ∆Hr‡ - T∆Sr‡

Question 22

How can we rewrite the ∆G relating to enthalpy

Answer 22

∆Hf‡ - ∆Hr‡ = ∆Go

Question 23

What does ‡ mean

Answer 23

activation energy
So ∆Hf‡ means the enthalpy of activation for the forward reaction.

Question 24

If we have values for ∆H‡ and ∆S‡ what deductions could be made

Answer 24

• Changes in ∆H‡ for similar reactions may indicate that rates of
  reaction are due to alterations in bond strengths.
• Values of ∆S‡ (positive or negative) may tell us whether reactions
  proceed by a DISSOCIATIVE or ASSOCIATIVE mechanism

Question 25

What is the conjugate base mechanism

Answer 25

In this mechanism the first step is formation of a conjugated base of the metal complex by deprotonating one of its ligands. This allows facilitated dissociation with one of the other ligands. The 5 coordinate intermediate picks up a new ligand.

Question 26

What is a better parameter than the activation parameter to deduce a mechanism

Answer 26

the volume of activation

Question 27

What does the volume of activation parameter tell us

Answer 27

tells us the volume change from moving from the starting ground state complex to its activated complex. It can be positive or negative and in some classes close to zero

Question 28

What is the volume of activation parameter measured by

Answer 28

the parameter is measured by looking at the effect of pressure on the reaction rate

Question 29

How do we calculate the volume of activation

Answer 29

a plot of ln(k/kp=0) vs P (MPa) will have a slope ‘s’ and so ∆V‡ = RT x S (cm3 mol-1 at 298.2 K) At another temperature tou would need to calculate R times T

Question 30

What are the units for ∆V‡

Answer 30

The units of R x T = J K-1 mol-1 x K = J mol-1 but the unit Joule can be broken down further since J = force x distance = N m. If we plot a graph of ln(k/k0) vs P in Pascals the slope would be 1/Pascals. Since a Pascal is a unit of pressure = force/area = Nm-2. Thus, the unit for R x T x slope = N m mol-1x 1/N m-2 = N m x N-1 m2 mol-1 = m3 mol-1.

Question 31

Define lability

Answer 31

the ability of a complex to engage in reactions that result in replacing one or more ligands by others.

Question 32

What is a labile comples

Answer 32

Complexes which undergo reactions that result in replacing one or more ligands by others very rapidly is known as labile

Question 33

What are inert complexes

Answer 33

If the reaction of replacing on or more ligands by others proceeds slowly or not at all are considered inert

Question 34

What is the classification by taube for labile metal ions

Answer 34

Labile metal ions have either a low-energy t2g orbital or at least one electron in a high energy eg orbital

Question 35

What is the classification by taube for inert metal ions

Answer 35

Inert metal ions will have at least one electron in each t2g orbital and no electrons in eg orbitals

Question 36

Define dissociative in terms of ligand binding

Answer 36

The ligand departs before the new ligand binds

Question 37

Define associative in terms of ligand binding

Answer 37

the new ligand binds before any ligands depart

Question 38

If we start from an octahedral complex and lose a ligand what shape do we produce

Answer 38

Square based pyramid

Question 39

If we start from an octahedral complex and gain a ligand what shape do we produce

Answer 39

An octahedral wedge

Question 40

What does CFAE stand for and what is it

Answer 40

Crystal field stabilisation energy (CFSE) calculated for ground state and transition state and difference defined as the Crystal Field Activation Energy (CFAE)

Question 41

What is the equation for CFAE

Answer 41

CFAE=CFSE(after) - CFSE(before)

Question 42

What does a negative CFAE tell us

Answer 42

A negative number tells us that it is favourable to move from an octahedra lgeometry to either a square-based pyramid or octahedral wedge. Labile complex

Question 43

What does a positive CFAE tell us

Answer 43

It is favourable to move from a square based pyramid or octahedral wedge to octahedral geometry Inert complex