Aspects of Transition metal chemistry applied to biological systems Flashcards
How does the bonding work between a metal and it’s ligand
The metal is the acceptor which forms a dative bond with the ligand donor
Electrons from the metal-centre of the ligand interact with the electrons from the ligand
What does this result in?
Resulting in a repulsive interaction, as both sets of electrons are negative
This causes the 3d electrons to go up in energy
What causes the further splitting of the 3d orbitals on this diagram?
The d-orbitals do not exist spherically in space, their charge is localised (i.e. tetrahedral, octehedral etc)
The arrangement in space affect how the orbitals split (i.e. an octehdral splitting is shown here)
What does the d-splitting orbtial diagram look like for an elongated octehedron and why?
An elongate octehedron has less repulsion in the z-direction and hence those orbitals are lower in energy
What does the d-orbital splitting diagram look like for a compressed octehedron?
A compressed octehedron has more repulsion in the z-direction, hence these orbitals are higher in energy
4d and 5d metals are always…
…low spin
What is the Irving Williams series?
The effect of varying the M(ll) central ion on the stabilities of transition metal complexes
What does Crystal Field Stabilisation Energy inform us of?
- CFSE measures the stabilisation energy due to the interaction between the metal ion and ligands
- e.g. CFSE = -1.2 means the d-electrons are occuping the lower-energy t₂g orbitals in a way which stabilises the system = low spin
- essentially the more negative CFSE, the more stable the complex is
What drives the pattern of the Irving Williams series?
1) From Mn(II) to Zn(II) there is an increase in the effective nuclear charge (this is responsible for the general increase in stability seen on the graph)
2) There is extra stability from Fe(II) to Cu(II) from the general trend. This is from crystal field stabilisation energy (0ΔO, -0.4ΔO, -0.8ΔO, -1.2ΔO, -0.6ΔO, 0ΔO)
3) However Cu(II) is an anomaly is due to the Jahn-Teller effect. When a complex has spin and orbital degeneracy, the complex will distort to remove degeneracy and achieve lower energy - mainly effect Cu(II)
What is a spin and orbital degeneracy?
- Degeneracy refers to the number of different quantum states that have the same energy
- Orbital degeneracy: This is why orbitals have the same energy levels (t₂g and eg orbitals)
- Spin degeneracy: Refers to te number of spin states available to a system e.g. a single electron can spin up or down
Jahn teller results in what type of distortion for copper?
When a complex like Cu has a spin and orbital degeneracy, the complex will distort to remove degeneracy and achieve a lower energy axial distortion (elongation) to remove degeneracy
The en ligand binds in the xy plane hence why it has such great stability in the Irving Williams Series
