Transition metals

Question 1

Properties of transition metals

Answer 1

• form compounds which are often paramagnetic
• shows variable oxidation states
• formed coloured ions and compounds
• form compounds with profound catalytic activity
• form stable complexes
• have high melting and boiling points

Question 2

What’s the chemistry of transition metals dominated by?

Answer 2

the d-orbitals (valence electrons are always 3d, not 4s) which are lower in energy than the s-orbitals

Question 3

The Lanthanide Contraction

Answer 3

• The ionic radii of the lanthanide ions decrease with increasing atomic number (they get heavier but smaller)
• f electrons do not shield very well but more protons are added

Question 4

What are ligands treated as?

Answer 4

point negative charges

Question 5

What is Δ _o ?

Answer 5

crystal field splitting parameter

Question 6

What do the symmetry labels e and t mean?

Answer 6

e = doubly degenerate
t = triply degenerate

Question 7

What sort of Δ do tetrahedral structures have?

Answer 7

Δ is always much smaller for tetrahedral complexes than square planar therefore they are almost always high spin

Question 8

How does crystal field splittings vary with oxidation state?

Answer 8

Δ are usually larger for metals in higher oxidation states because the higher charge on the metal exerts more attraction to the ligands resulting in shorter bond lengths and more interaction between d-orbitals and ligand charge

Question 9

Factors affecting Δ _o

Answer 9

• oxidation state of metal
• position on periodic table
• type of ligand

Question 10

How does crystal field splitting vary with position on periodic table?

Answer 10

Δ are usually smaller for the 1st row and so first row transition metals have a tendency of being high spin

Question 11

Δ link to wavelength

Answer 11

small splitting at higher wavelengths (red)
large splitting at smaller wavelengths (purple)

Question 12

What is Δ _o measured between in a MO diagram?

Answer 12

t _2g and e _g ^*

Question 13

General trend of the spectrochemical series for crystal field splittings

Answer 13

⫪- donor < weak ⫪- donor < no ⫪ effects < ⫪- acceptor

(⫪- donor make Δ smaller)

Question 14

What are the different light absorption and electronic transitions?

Answer 14

• Intra-atomic (localised) excitations
• Interatomic (charger transfer) excitations
• Molecular Orbital (HOMO to LUMO) excitations
• Band to band transitions
• Intraband excitations
• Defects and colour centres

Question 15

What are the 2 key light absorption and electronic transitions for transition metals?

Answer 15

• Intra-atomic (localised) excitations
• Interatomic (charger transfer) excitations

Question 16

What are the selection rules for transitions?

Answer 16

Spin selection rule, ΔS = 0
Laporte selection rule, Δl = +/- 1 because a change in parity is required for complexes with an inversion centre, i

Question 17

When can the selection rules for transitions be relaxed?

Answer 17

• Spin forbidden transitions are ‘partially allowed’ because of spin-orbit coupling
• Laporte rule is relaxed if there’s no centre of symmetry because of orbital mixing

Question 18

What is ε in the beer lambert law?

Answer 18

a molecules ability to absorb light at a given wavelength

Question 19

What type of transition is Fe(II) → Fe(III)?

Answer 19

electron transition is a low energy transition therefore absorbs in the red region