Why oxygen, cannot act as a pi-donor while NO can?

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Discussion Overview

The discussion revolves around the question of why oxygen cannot act as a pi-donor while nitric oxide (NO) can. It explores the concepts of pi-donors and pi-acceptors in coordination chemistry, with a focus on the electronic properties of oxygen and NO.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants clarify that pi-donors are ligands that donate pi electrons to a metal center, while pi-acceptors accept electrons from filled d(pi) orbitals.
  • One participant questions whether the assertion that oxygen cannot act as a pi-donor is based on a lack of examples or established knowledge.
  • A participant mentions that their professor stated oxygen cannot act as a pi-donor, prompting further inquiry into the reasoning behind this claim.
  • Another participant raises questions about the definitions of pi bonds and pi electrons, suggesting a connection to molecular oxygen's paramagnetic nature and its unpaired electrons.
  • It is proposed that oxygen can act as a pi-donor but does so infrequently due to its electronegativity, which generally discourages electron donation.
  • Participants discuss the formation of nitrosyl species with NO as a pi-donor and contrast this with the rarity and high energy of dioxygenyl ions for oxygen.
  • One participant challenges another's understanding of pi bonds and suggests that the discussion should focus on molecular orbital (MO) theory rather than Lewis structures.
  • A request is made for examples of oxygen acting as a pi-donor, indicating a desire for further clarification on the topic.

Areas of Agreement / Disagreement

Participants express differing views on the ability of oxygen to act as a pi-donor, with some asserting it can while others maintain it cannot. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

There are unresolved questions regarding the definitions of pi bonds and electrons, as well as the implications of molecular oxygen's electronic structure. The discussion also reflects varying levels of understanding among participants.

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Hi,

I have learned that pi-donor are those ligands which donate their pi electrons to metal centre while pi-acceptor accepts electron from filled d(pi) orbital to their pi* orbital.
Now, I'm confused, why oxygen, having two pi* electrons cannot act as a pi-donor while NO, having one pi* electron only can?

Thank you!
 
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Have you actually been told that oxygen cannot act in this way, or is it more that you haven't seen any examples yet?
 
Actually my professor said so, but I just wonder why
 
What is a pi bond? Is it present in an oxygen atom?

What is a pi electron? How does it relate to a pi bond?

edit: It just occurred to me that you might be referring to molecular oxygen. If that is the case, you should know that oxygen is paramagnetic... that is, it has two unpaired electrons. Try to resolve that bit of information with the Lewis structure!
 
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Oxygen can act as a pi-donor. It seldom does because oxygen is electronegative and simply doesn't like donating electrons in general, pi or otherwise.

NO can act as a pi donor because you can form a nitrosyl species, e.g. when binding to a metal atom:
M+..NO* <->M-NO+

The corresponding dioxygenyl ion for oxygen is very rare and very high in energy. OTOH oxygen can act as a d-acceptor, forming a superoxo-species. (pretty much all the oxygen-consuming reactions in biology are performed by metal centers in enzymes, e.g. cytochrome c oxidase.)

chemistree: You don't know what a pi bond is, or you're not using your head? Of course he's talking about molecular oxygen. And why bring up Lewis structures when the discussion is already phrased in terms of more sophisticated MO theory?
 
alxm said:
Oxygen can act as a pi-donor. It seldom does because oxygen is electronegative and simply doesn't like donating electrons in general, pi or otherwise.

Please name one. I'd be very interested to learn about it.
 

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