Thermodynamic Effects of Crystal Field Theory

Question 1

In an octahedral field how much is the complex statbilised/destabilised by with each electron placed in t2g or eg

Answer 1

1. Each electron placed in one of the lower t2g= 0.4Do
2. Each electron placed in one of the eg orbitals destabilises the complex by 0.6Do with respect to the spherical field case

Question 2

For octahedral case explain how the CFSE changes from d1-d10

Answer 2

1. CFSE increases from d1 to d3
2. Decreases again up to d5
3. Rises to a maximum at d8
4. Decreases again up to d10

Question 3

For tetrahedral case explain how the CFSE changes from d1-d10

Answer 3

1. Same pattern as octahedral

2. Dt = 4/9 Do so the effects will consequently be smaller

Question 4

Are there low-spin tetrahedral complexes in first row transition metals

Answer 4

1. Dt is relatively small so there are no low-spin tetrahedral complexes of the first row transition metals

Question 5

What happens to hydration enthalpies for M2+ and M3+ ions

Answer 5

1. Expected to become more negative across the series because of a contraction in radius resulting from the increase in effective nuclear charge Zeff

Question 6

Define hydration energy and show example M n+

Answer 6

1. Enthalpy change when 1 mole of gaseous ions is completely dissolved in water to form aqueous ions
2. M n+ (g) –> [M(H2O)6]n+ (aq)

Question 7

What is observed when looking at hydration energies of M2+ ions

Answer 7

1. A linear trend is observed

2. But is perturbed by CFSEs which give the curve a double humped appearance

Question 8

Where is H2O in the SCS and does it create a weak or strong field

Answer 8

1. It is midway along the SCS for ligands and does not create a strong field

Question 9

Are 3d M2+ ions low or high spin

Answer 9

1. High-spin

Question 10

What CFSE values do d0, d5 and d10 have and what geometry do they prefer

Answer 10

1. 0 CFSE values

2. no preference between octahedral and tetrahedral coordination

Question 11

If you subtract CFSE from DH hyd for each d electron configuration what do you get

Answer 11

1. Gives rise to a straight line

Question 12

On the CFSE graph what is the energy scale

Answer 12

1. It is negative

2. Lowest points represent greatest stabilisations

Question 13

Where is Cl- in the spectrochemical series

Answer 13

1. Lower

2. All complexes have high spin

Question 14

When is the strongest preference for octahedral geometry

Answer 14

1. Expected for d3 and d8 ions in the absence of any other factors

Question 15

What is the Irving-Williams Series

Answer 15

1. Summarises the relative stabilities of complexes formed by M2+ ions
2. Reflects combination of electrostatic effects and LFSE
3. Order is relatively insensitive to choice of ligands, but ligand has to be able to replace water at a metal core

Question 16

Order Fe2+, Mn 2+, Zn2+, Ni2+, Co2+, Cu2+ according to the Irving-Williams Series

Answer 16

1. Mn2+< Fe2+< Co2+ < Ni2+ < Cu2+ < Zn2+

Question 17

Explain the order of the Irving-Williams Series

Answer 17

1. In general the increase in stability correlates inversely with ionic radius- suggesting it reflects electrostatic effects
2. But strong increase for Fe2+ plus which all have strong field ligands
3. THese ions experience an additional stabilisation proportional to the extra-ligand-field stabilisation energies in the complexes
4. Cu2+ has greater stability than Ni2+ despite having e- in eg- due to Jahn Teller effects