Lecture 9

Question 1

Define inert

Answer 1

Complexes that are thermodynamically
unstable but survive for long periods (at least
a minute) are called inert

Question 2

Define labile

Answer 2

Complexes that undergo more rapid
equilibration are called labile

Question 3

Write an equation to show ligand substitution in octahedral complexes

Answer 3

ML6 + X = ML5X + L

Question 4

State the factors affecting rate of substitution

Answer 4

1. oxidation state of metal
2. distribution of 3d electrons

Question 5

How does the oxidation state of the metal influence rate?

Answer 5

• Rates are slower for ions with higher charge
  this is because M3+ is smaller and higher charged
• metal ligand bonds harder to break (SN1 harder)
• there is less space for attack by the incoming ligand X (SN2 harder)

Question 6

How does the distribution of 3d electrons in high spin complexes influence rates?

Answer 6

octahedral high spin complexes;

from d0 (Ca2+) to d3 (V2+) rates drop;
- The metal ion nuclear charge increases.
- Since the electrons go into the orbitals pointing in between the ligands, Zeff felt by the ligands increases and the M-L
bonds get stronger.
- The electrons in dxy, dxz, dyz protect the metal from an attack by an incoming ligand

d3 (V2+) to d5 (Mn2+) rates rise;
- the 4th and 5th electron go into the orbitals pointing at the ligands. This makes the M-L bonds weaker
- the electrons dont protect from attack

d5 (Mn2+) to d8 (Ni2+) rates drop;
- the electrons go into the orbitals lying in between the ligands

d8 (Ni2+) to d10 (Zn2+) rates rise
- the electrons go into the orbitals pointing at the ligands

• d4 (Cr2+) and d9 (Cu2+) complexes are distorted- Jahan teller distortion so lower activation energy

Question 7

How does the distribution of 3d electrons in low spin complexes influence rates?

Answer 7

Here we go on putting electrons into the low energy
orbitals pointing in between the ligands.
rates: d3> d4> d5> d6&laquo_space;d7