Hey guys... I don't post here often but i'm absolutely stuck..
Its to do with crystal field theory. I generally understand the concepts but now i've got to this Jahn Teller stuff and i just can't see any light!
The problem is i have a question to do...
i have to sketch the crystal field splitting diagram for an octahedral low spin d5 and low spin d7 complex.
I can do everything apart from decide what is Low and high spin. and also what type of distortion will be in the d5 complex and how to find out.
If anyone can help i would be very grateful!
Many Thanks, Zain
The distinction of high spin/low spin only applies to octahedral molecules with d4, d5, d6, and d7 electronic configurations.
For configurations d4 to d7, there are two ways in which the electrons can be placed into the t2g and eg orbitals which depend on the magnitude of o (the gap between the two levels).
In the weak field case (also called high spin of spin free), the electrons are distributed one at a time, with parallel spins before pairing as if the d-orbitals were still degenerate. In the strong field case (also known as low spin or spin paired), the electrons first fill the t2g set. For configurations d1 to d3 and d8 to d10 there is no difference.
With d4-d7 metals, there is at least one electron pair for strong field ligands in the t2g energy level, and at least one empty orbital in the eg energy level.
This allows for a decrease in pairing with a weak field ligand, and thus differering paramagnetism between weak field and strong field ligands, e.g. for d5 metals:
eg two spin up unpaired --- ----
tg three spin up unpaired ---- ---- ----
eg empty ---- ----
tg all five fill this level (four paired and one unpaired) ---- ---- ----
Jahn Teller Effect:
NUMBER OF ELECTRONS: 1 2 3 4 5 6 7 8 9 10
HIGH SPIN W W S W W S
LOW SPIN W W W W S S
W: weak Jahn-Teller effect (t2g orbitals unevenly occupied)
S: strong Jahn-Teller effect expected (eg orbitals unevenly occupied),
blank: no Jahn-Teller effect expected.