[Winga]

If not, then why?

[AWK]

Yes, they exist.
http://www.ilpi.com/organomet/alkene.html
http://www.chem.ucalgary.ca/groups/ziegler/Chem629/lect16/lect16.index.html

[Winga]

One thing I really want to ask is that the raising in energy of d-orbitals in an octahedral complex.

For a free metal ion (e.g. d5), the d-orbitals are degenerate. When the 6 ligands attach to the M+ at octahedral positions, the energies of d-orbitals will raise in different extent due to the different extents of electronic repulsion between ligands lone pairs and d-electrons.

Now, if the metal ion is d0, it seems that there is no any electronic repulsion with ligands line pairs. So, how does the orbitals split? Or there is no such kind of complex?

[Garneck]

What about CaEDTA? Can that count as a d0 complex?

[Major Werner]

Yes they do exist. a notable example is Ti (IV) complexes which ave been characterised.

[Winga]

Then, is the splitting between e_g and t_2g still existed?

We can not classify the d0 complexes as neither high spin nor low spin, right?

[Major Werner]

Yes, winga, the splitting occurs mainly as a result of the interactions the ligand has with the d-orbitals. this is expressed by the ligand field theory. so under d0 you'll still have your t2g and eg for Oh and t2 and e for Td cplxes.

[moussa]

electronic configuration says ns np (n-1)d
so isn't it possible?
it is said to be having filled p orbital but no electrons to occupy d
1s(2) 2s(2)  2p(6)3s(2) 3p(6) 4s(2) 3d(0)  summ of 20 lectrons

[ksr985]

isnt permanganate ion MnO4 (-) a d0 complex? so is dichromate ion. Cr2O7 (2-)

[maxyoung]

Consider how you construct the MO diagrams for transition metal complexes. You don't consider the number of d electrons on the metal center until you have drawn all MOs, right? Before that, the only thing to be considered is the symmetry and energy of individual atomic orbitals. If they fulfill certain criteria, they will interact. The number of d e is important only when you try to fill the MOs, but this doen't affect the appearence of MO diagram--the eg and t2g oritals still exit, but they are empty. So d0 complexes have nothing special.

It's a bit hard to explain this in term of electronic repulsion. Remember crystal field theory has quite a number of limits. Don't bother yourself using it to explain everything.