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Topic: pi-donor,sigma-donor, pi acceptor  (Read 77477 times)

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Offline AdiDex

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Re: pi-donor,sigma-donor, pi acceptor
« Reply #15 on: September 16, 2014, 01:28:56 PM »
Okk.....i read it wrong....

Offline kriggy

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Re: pi-donor,sigma-donor, pi acceptor
« Reply #16 on: September 16, 2014, 02:42:09 PM »
Haha, happens to me like.. all the time :D
If you have more questions regarding this topic or similar feel free to ask

Offline AdiDex

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Re: pie-donor,sigma-donor, pie acceptor
« Reply #17 on: October 16, 2014, 02:51:29 AM »
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?  :rarrow: sigma donor
b) has more than 1 electron pair at coordinating atom?  :rarrow: sigma and pi donor
c) has double or tripple bond at coordinating atom?  :rarrow: sigma donor and pi acceptor
d) is the ligand coordinating by phosphorous?  :rarrow: sigma donor and d acceptor

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

Offline kriggy

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Re: pi-donor,sigma-donor, pi acceptor
« Reply #18 on: October 19, 2014, 02:32:16 PM »
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)

Offline AdiDex

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Re: pi-donor,sigma-donor, pi acceptor
« Reply #19 on: October 19, 2014, 11:57:00 PM »
Hmm.. Seems logical . Thank you... :)

Offline Irlanur

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Re: pi-donor,sigma-donor, pi acceptor
« Reply #20 on: October 20, 2014, 10:20:32 AM »
Quote
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)

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