Core 2: Transition Metals

Question 1

What assumption is made by crystal field theory?

Answer 1

All interactions are hard

Question 2

What isomers can exist for [MX₄Y₂] and [MX₃Y₃]?

Answer 2

[MX₄Y₂] - cis and trans isomers

[MX₃Y₃] - mer and fac isomers

Question 3

What spin states do tetrahedral complexes typically take and why?

Answer 3

They form high spin complexes as the pairing energy is high compared to Δ_T

Question 4

Explain the basis of the 2 rows of orbital energies

Answer 4

Orbitals that point at ligands are less energetically favourable when they are filled with electrons as they repel the ligands.

Question 5

What are the 3 sets of complimentary colours?

Answer 5

Red-Green

Orange-Blue

Yellow-Violet

Question 6

What is the equation for the effective magnetic moment and what is it measured by?

Answer 6

μ_eff = (n(n+2))^½

Measured by a Gouy balance.

Question 7

Describe the polarisability of the first row ions, what demonstrates this trend?

Answer 7

The get softer (more easily polarised) left to right however all zero ox. state atoms are soft. Naturally left elements are normally oxides and right elements are normally sulfides.

Question 8

What letter summerises formation constants for multiple substitutions?

Answer 8

β_n where n is the number of H₂O ligands replaced by L.

Question 9

How do the crystal field enviroments change from a tetragonal structure to a square planar structure?

Answer 9

In square planar the d_z² orbital is lower than the d_xy orbital as the ligands from the z axis are removed so all z character orbitals are stabilised.

Question 10

When are tetrahedral structures favoured over octahedral?

Answer 10

When M is small and L are large.

Question 11

Define a metal complex

Answer 11

A metal lewis acid with a number of ligand lewis bases

Question 12

How can you tell if a molecule is chiral?

Answer 12

If it hasn’t got a plane of symmetry it is chiral.

Question 13

Define coordination number, what does it depend on?

Answer 13

The number of donor atoms M is bonded to.

It depends on: the size of M, the steric interactions of the ligands and the electronic interactions

Question 14

What are charge transfer transitions? What do the energy of these transitions depend on?

Answer 14

When electrons move from metal to ligand, ligand to metal or even metal to metal.

The energy depends on:

1. The oxidising power of the metal
2. The reducing power of the ligand

Question 15

How can k_f be determined?

Answer 15

Potentiometry(acc. pH) if there is a pH change, spectroscopically such as UV/Vis, fluorimetry and proton NMR.

Question 16

What is the highest oxidation state that forms? What trend is this the limit of?

Answer 16

+7 for Mn, the group oxidation states

Question 17

Give the general trend and example of the nature of the ligands and their field strengths

Answer 17

Halogen and sulfur ligands are the softest(I^- and SCN^-), then oxygen based(OH^- is weaker than H₂O), then nitrogen based(SCN^- and NH₃), then ligands that resonate to form double bonds with the metal(CN^- and CO).

Soft ligands have weak fields.

Question 18

What electron configuration form square planar complexes? Why?

Answer 18

d⁸ due to the stabilisation of the cfse. The d_x²-y² orbital is significantly raised in energy and is unoccupied as a result.

Question 19

What is the definition of a transition metal?

Answer 19

An element that has partly filled d or f subshells

Question 20

What are the most common oxidation states for transition metals? Where are they common and why does this occur?

Answer 20

+2 and +3, +3 to the left and +2 on the right as Z_eff increases

Question 21

How do you calculate cfse for octahedral complexes?

Answer 21

-n(0.4Δ_O)+m(0.6Δ_O)+πP

Where π is the number of optional pairs made and P is the paring energy.

Question 22

How do you define the optical isomerism of M(en)₂ or equivalent bidentate ligands?

Answer 22

Rotate the structure to the typical 2 axial, 4 planar view. Rotate about the axial axis untill the top position has its connection going backwards. If the connection goes to the right then the isomer is Δ, if the connection goes to the left then the isomer is Λ.

Question 23

What is the Jahn-Teller theorem? What 3 complexes does it have an effect on? What is the effect?

Answer 23

If electrons are unequally distributed between degenerate orbitals, the complex will distort to achieve a lower energy. d⁷ low spin, d⁴ high spin and d⁹. Z axis bonds get longer so z character orbitals lower in energy, this is tetragonal distortion. This has big kinetic implications.

Question 24

What is ferromagnatism?

Answer 24

Below the Curie temperature a metal will have weiss domains where spins allign. They will also allign very well in an applied field.

Question 25

What does the rate of substitution of ligands depend on?

Answer 25

1. Ox. state of the metal, rates are slower for highly charged ions
2. Distribution of d electrons, electrons between ligands repel attacks, electrons facing ligands weakens bonds
3. Distortion of shape/bond length via the Jahn-Teller effect

Question 26

How are Δ_O and Δ_T related?

Answer 26

Δ_T=4/9xΔ_O

Question 27

What decides the absorbance intensity of a complex?

Answer 27

The selection rules:

1. Laporte - the quantum number l must change by +1 or -1, d→d is forbidden
2. Parity - symmetry of the orbitals must change, this is broken as complexes vibrate
3. Spin - very few transitions where the spin changes will occur

Question 28

Draw the structures of the following abbreviated ligands: acac, en, bipy, edta and py.

Answer 28

Question 29

What 3 factors affect the magnitude of field splitting?

Answer 29

1. Coordination geometry and the number of ligands
2. The nature of the ligands, if they’re hard or soft
3. The nature of the metal ion, high ox. states lead to large splitting

Question 30

How do you calculate Δ_O from the wavelength of a photon absorbed?

Answer 30

Δ_O=ṽ x 0.012