Crystal Field Theory Flashcards
What does splitting depend on?
Arrangement and type of ligands
Octahedral crystal field
Ligands point along x, y and z axes so the orbitals that lie along these are repelled more strongly so dx2-y2 and dz2 increase in energy form eg and others form lower t2g level
Tetrahedral crystal field
No orbitals pointing directly at ligands, dxy, dxz and dyz pont in general direction of 4 ligands and form t2, others don’t and form e with inverse ordering to octahedral
Why is splitting energy much lower for tetrahedral compared to octahedral?
in tetrahedral no orbitals point directly at ligands so electron repulsion is much smaller
Crystal field stabilisation energy
Energy of stabilisation obtained by complex relative to state of no d-orbital splitting
Pairing energy
Energy needed to pair 2 electrons in an orbital
Low spin pairing energy
Less than delta o
High spin pairing energy
Greater than delta o
Nature of ligands
Weak field ligands have small octahedral splitting and are high-spin and strong field ligands have large octahedral splitting and are low-spin
Diamagnetic
Magnetic moment = 0, no unpaired electrons
Paramagnetic
Magnetic moment > 0, has unpaired electrons
When s square planar geometry preferred?
Strong field ligands and 2nd/3rd row metals
When s tetrahedral geometry preferred?
Weak-field ligands and 1st row metals
Square planar crystal field splitting
Start with octahedral splitting
t2g splits into eg (dyz and dxz) which decreases in energy and b2g (dxy) which increases in energy
Eg splits into a1g (dz^2) which decreases in energy and b1g (dx^2-dy^2) which increases in energy
B2g has a higher energy than a1g
