# Why is the N-N bond length greater in dinitrogen trioxide than in dinitrogen tetroxide?

Why is the N-N bond length greater in dinitrogen trioxide than in dinitrogen tetroxide?

If the lone pair on $\ce{N}$ in $\ce{N2O3}$ delocalises, then the $\ce{N-N}$ bond will have a double bond character, so it should be shorter.

From data on Wikipedia, the $\ce{N-N}$ bond length in dinitrogen trioxide is $\pu{186.4pm}$ while that of dinitrogen tetroxide is $\pu{178pm}$.

• I am thinking this is a very tough question. Here's a research paper on this topic. Read from "The $\ce{N–N}$ bond distance is exceptionally long $\pu{1.75–1.78 Å}$! while the..." second paragraph. – Gaurang Tandon Feb 24 '18 at 2:24
• @GaurangTandon This paper highlights that N-N bond is exceptionally long in dinitrogen teroxide. But why is it longer in dinitrogen trioxide? – Parth Mall Feb 24 '18 at 4:28
• Indeed, it is. But, I do not know the exact answer. I was just linking to a related paper. – Gaurang Tandon Feb 24 '18 at 4:29
• So is this an anomaly or is there an explanation to it? – Parth Mall Feb 24 '18 at 6:58
• @Parth there is no such thing as an anomaly , just things for which reasons haven't been found yet. – Avnish Kabaj Feb 24 '18 at 9:34