[AdiDex]

Okk.....i read it wrong....

[kriggy]

Haha, happens to me like.. all the time
If you have more questions regarding this topic or similar feel free to ask

[AdiDex]

Yes, it is sigma donor (basicaly all ligands are sigma donors but some of them can be pi donors/acceptors in addition). It has only 1 electron pair so its only sigma donor.
How can you tell? Well from examples we were told at lectures (It most likely will not fit all possible ligands):
a) has only 1 electron pair at coordinating atom?  sigma donor
b) has more than 1 electron pair at coordinating atom?  sigma and pi donor
c) has double or tripple bond at coordinating atom?  sigma donor and pi acceptor
d) is the ligand coordinating by phosphorous?  sigma donor and d acceptor

Why did you said that ligand should have double or triple bond for sigma donor and pi acceptor..?

[kriggy]

Because the back donation goes into pi-antibonding orbitals. And for them to exist, you need pi bond.
Or at least that is my reasoning (we didnt cover it that much at class)

[AdiDex]

Hmm.. Seems logical . Thank you...

[Irlanur]

Because the back donation goes into pi-antibonding orbitals. And for them to exist, you need pi bond.

That's not true. the symmetry of an orbital concerning ligand-symmetry has nothing to do with the symmetry of this orbital in a complex. (of course there are cases which exist more often than others...)

consider di-hydrogen. the sigma-bonding orbital of H2 can be used as a sigma-donating orbital in a complex. the sigma-antibonding orbital of H2 has pi-symmetry in a complex and can serve as a pi-acceptor. (provided that the binding is side-on and not end-on)