The Nitronium ion, which is a positively charged ligand, in which the donor atom is Nitrogen. The question is, that Nitrogen has a total of 5 electrons, it shares 2 with oxygen and donates 2 electrons to another oxygen and also looses one electron to form a cationic $\ce{NO2+}$. It does not have a lone pair, not even a single electron. How is it a ligand?

@Dissenter: You explain nitronium for the nitration of benzene, in which a covalent bond is formed. I would like to know this for a coordination bond.

I do not have any example, but I see the nitronium ion as a example in a book of PRADEEP publication which is a TRUSTED publisher.

  • $\begingroup$ Are you sure it's not nitro/nitrite, anionic NO2? $\endgroup$ – jerepierre Oct 4 '14 at 16:24
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    $\begingroup$ Where did you see nitronium described as a ligand in a metal complex? I don't believe nitronium can be, but perhaps you are looking at some unusual situation. The community needs more information to answer the question. $\endgroup$ – jerepierre Oct 5 '14 at 13:51
  • $\begingroup$ U say about hydrogen proton as a ligand..... can u explain me how it is $\endgroup$ – nilesh Oct 6 '14 at 9:51
  • $\begingroup$ thanks for your approach.....search. the regarding information as soon as possible.... pradeep publication is of India $\endgroup$ – nilesh Oct 6 '14 at 9:58
  • $\begingroup$ I have edited your post and tried to clarify what you are actually asking. (I might have terribly failed at this.) Could you please provide the reference, where you found this obscurity. A full citation and a screenshot of the relevant section would be much appreciated. $\endgroup$ – Martin - マーチン Oct 6 '14 at 10:26

A ligand is ...

In an inorganic coordination entity, the atoms or groups joined to the central atom.

In biochemistry: if it is possible or convenient to regard part of a polyatomic molecular entity as central, then the atoms, groups or molecules bound to that part are called ligands. Biochemical usage is thus wider, in that the central entity can be polyatomic. Thus H+ may be a ligand for proteins ...


Therefore, yes, there can be ligands which do not possess lone pairs. One being the hydrogen proton. It doesn't have any electrons at all.

Regarding the nitronium ion - yes - the central nitrogen doesn't have a lone pair - but that doesn't mean it can't participate in coordination chemistry. If the N had a lone pair and could donate it to something, then that N would be a Lewis base. An example of a Lewis base is ammonia. Since the N in nitronium ion has no lone pairs, but it can form complexes with other molecules - the N in nitronium ion is instead a Lewis acid. What happens usually is that some Lewis base attacks the N in nitronium ion and one of the N=O bonding pairs becomes an oxygen lone pair. This free the central N up for bonding. Consider the bottom left part in this graphic:

enter image description here


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