I collected some data to determine the value of $\Delta_\text{o}$ for a some transition metal complexes (attached) and I'm very confused as to why $\Delta_\text{o}$ for the $\ce{ONO-}$ ligand is higher than $\ce{H2O}$. I would think that the $\ce{ONO-}$ is a better $\pi$ donor than $\ce{H2O}$ so $\text{t}_{2\text{g}}$ would be raised higher in energy and therefore $\Delta_\text{o}$ would be lower.

Similarly, I am confused as to why $\ce{ONO-}$ is not a $\pi$ acceptor and does not have a similar value for $\Delta_\text{o}$ as $\ce{NO2-}$ or why $\ce{NH3}$ is higher than $\ce{ONO-}$?

It is most likely that my thinking is wrong but I would really appreciate it if someone could explain this to me!

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  • 2
    $\begingroup$ I personally wouldn't think that a 1kJ mol-1 difference has any significance within the accuracy expected from the model being applied $\endgroup$
    – Ian Bush
    Feb 14 at 7:28


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