[djiang87]

In my revision exercises the teacher gave us, he gives us two compounds, the first is [Fe(CN)₆]^3- and the second one is [Fe(H2O)₆]³⁺.

turns out the first one is low spin and the second one is high spin. Im not too sure how to work this out.

[darko]

CN^- cause higest octahedral split then H₂O , so energy of pairing electrons is lower then enrgy of delta_o

[djiang87]

how would i know that CN- causes a higher octahedral split?

[darko]

there is several factors to that determine  :delta:_o , it depends on pairing energy of electrons, energy of  transition of d-electrons, charge of central metal ion. so it could not be absolute value of ligands, it is relative and is experimental data (measuring magnetic propertis or absorbtion spectra). for most comon ligands you get series

I^-<Br^-, Cl^- < SCN^- (S bonding)< F^-, OH^-<C₂O₄^2-< H₂O<SCN^-  (N bonding)<NH₃,py<en<SO₃^2-<dipy,NO₂^- (N bonding)<CN^-<CO

[Trl]

Read up on crystal field theory?

Here is a page which looked decent enough:

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch12/crystal.php

[darko]

or you can read mentioned link

[djiang87]

Thanks for the responses guys. Ive got my exam in a couple of hrs, your help was much appreciated =]