How to calculate cfse?

Answer 1

crystal field splitting energy is actually the barrier the degenerate d-orbitals which undergo further splitting due the approach of ligand into low lying "t2g" level and higher "eg" while forming a complex. it explains the stability and structure of the complex.

so the energy required for an electron to excite from t2g level to eg level is associated with some energy which is equal to this barrier of energy. this is give in general in terms of absobption bands i.e in terms of wave no. in the problems. the amount of energy or wave no. is equal to the delta not, the octa hedral spliting energy.

with the addition of one electron with accordance to Hunds rule, the energy rise by =+2/5∆o in the eg level and =-3/5∆o in eg level.so when we multipy the no. of electrons with these two values based on their position in these two level, and add the values of t2g and eg levels we get the cfse of of octahedral complex. i.e

==> 2/5*(no.of e in t2g)+(-3/5)(no.of e in eg level)=∆o

the square planar is another important structure which is regularly seen. the splitting of orbitals is exactly oppsite. hence the ∆o value given need to be taken exactly the oppsite for t2g level and eg level.

sq.planar and octahedral energies are related as

4/9∆o=∆t

where ∆t is the energy of splitting in the squarplanar complex.